Targets, scopes, vars

71 files changed, 1144 insertions, 1002 deletions

diff --git a/build2/b.cxx b/build2/b.cxx
index f359dbc..6a49cb7 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -590,6 +590,8 @@ main (int argc, char* argv[])
                     ? optional<size_t> (ops.max_stack () * 1024)
                     : nullopt));
 
+    // @@ CTX: should these be per-context?
+    //
     variable_cache_mutex_shard_size = sched.shard_size ();
     variable_cache_mutex_shard.reset (
       new shared_mutex[variable_cache_mutex_shard_size]);
@@ -606,10 +608,11 @@ main (int argc, char* argv[])
       trace << "jobs: " << jobs;
     }
 
-    // Set the build state before parsing the buildspec since it relies on
-    // global scope being setup.
+    // Set the build context before parsing the buildspec since it relies on
+    // the global scope being setup. We reset it for every meta-operation (see
+    // below).
     //
-    variable_overrides var_ovs (reset (cmd_vars));
+    unique_ptr<context> ctx (new context (sched, cmd_vars));
 
     // Parse the buildspec.
     //
@@ -619,7 +622,7 @@ main (int argc, char* argv[])
       istringstream is (args);
       is.exceptions (istringstream::failbit | istringstream::badbit);
 
-      parser p;
+      parser p (*ctx);
       bspec = p.parse_buildspec (is, path ("<buildspec>"));
     }
     catch (const io_error&)
@@ -745,13 +748,14 @@ main (int argc, char* argv[])
       else
         opspecs.assign (lifted, 1);
 
-      // Reset the build state for each meta-operation since there is no
+      // Reset the build context for each meta-operation since there is no
       // guarantee their assumptions (e.g., in the load callback) are
       // compatible.
       //
       if (dirty)
       {
-        var_ovs = reset (cmd_vars);
+        ctx = nullptr;
+        ctx.reset (new context (sched, cmd_vars));
         dirty = false;
       }
 
@@ -778,15 +782,16 @@ main (int argc, char* argv[])
           // Can modify params, opspec, change meta-operation name.
           //
           if (auto f = meta_operation_table[m].process)
-            mname = current_mname =
-              f (var_ovs, mparams, opspecs, lifted != nullptr, l);
+            mname = current_mname = f (
+              *ctx, mparams, opspecs, lifted != nullptr, l);
         }
       }
 
       // Expose early so can be used during bootstrap (with the same
       // limitations as for pre-processing).
       //
-      global_scope->rw ().assign (var_build_meta_operation) = mname;
+      scope& gs (ctx->global_scope.rw ());
+      gs.assign (var_build_meta_operation) = mname;
 
       for (auto oit (opspecs.begin ()); oit != opspecs.end (); ++oit)
       {
@@ -978,7 +983,7 @@ main (int argc, char* argv[])
               // Handle a forwarded configuration. Note that if we've changed
               // out_root then we also have to remap out_base.
               //
-              out_root = bootstrap_fwd (src_root, altn);
+              out_root = bootstrap_fwd (*ctx, src_root, altn);
               if (src_root != out_root)
               {
                 out_base = out_root / out_base.leaf (src_root);
@@ -1023,8 +1028,7 @@ main (int argc, char* argv[])
           // use to the bootstrap files (other than src-root.build, which,
           // BTW, doesn't need to exist if src_root == out_root).
           //
-          scope& rs (
-            create_root (*scope::global_, out_root, src_root)->second);
+          scope& rs (create_root (gs, out_root, src_root)->second);
 
           bool bstrapped (bootstrapped (rs));
 
@@ -1238,7 +1242,7 @@ main (int argc, char* argv[])
                 fail (l) << "unexpected parameters for meta-operation "
                          << mif->name;
 
-              set_current_mif (*mif);
+              ctx->current_mif (*mif);
               dirty = true;
             }
 
@@ -1427,9 +1431,9 @@ main (int argc, char* argv[])
           // So we split it into two passes.
           //
           {
-            auto& sm (scope_map::instance);
+            auto& sm (ctx->scopes.rw ());
 
-            for (const variable_override& o: var_ovs)
+            for (const variable_override& o: ctx->var_overrides)
             {
               if (o.ovr.visibility != variable_visibility::normal)
                 continue;
@@ -1450,7 +1454,7 @@ main (int argc, char* argv[])
               v = o.val;
             }
 
-            for (const variable_override& o: var_ovs)
+            for (const variable_override& o: ctx->var_overrides)
             {
               // Ours is either project (%foo) or scope (/foo).
               //
@@ -1504,7 +1508,7 @@ main (int argc, char* argv[])
           // building before we know how to for all the targets in this
           // operation batch.
           //
-          const scope& bs (scopes.find (ts.out_base));
+          const scope& bs (ctx->scopes.find (ts.out_base));
 
           // Find the target type and extract the extension.
           //
@@ -1546,7 +1550,7 @@ main (int argc, char* argv[])
         } // target
 
         if (dump_load)
-          dump ();
+          dump (*ctx);
 
         // Finally, match the rules and perform the operation.
         //
@@ -1558,7 +1562,7 @@ main (int argc, char* argv[])
           if (mif->operation_pre != nullptr)
             mif->operation_pre (mparams, pre_oid); // Cannot be translated.
 
-          set_current_oif (*pre_oif, oif);
+          ctx->current_oif (*pre_oif, oif);
 
           action a (mid, pre_oid, oid);
 
@@ -1570,7 +1574,7 @@ main (int argc, char* argv[])
               mif->match (mparams, a, tgs, diag, true /* progress */);
 
             if (dump_match)
-              dump (a);
+              dump (*ctx, a);
 
             if (mif->execute != nullptr && !ops.match_only ())
               mif->execute (mparams, a, tgs, diag, true /* progress */);
@@ -1585,7 +1589,7 @@ main (int argc, char* argv[])
           tgs.reset ();
         }
 
-        set_current_oif (*oif, outer_oif);
+        ctx->current_oif (*oif, outer_oif);
 
         action a (mid, oid, oif->outer_id);
 
@@ -1597,7 +1601,7 @@ main (int argc, char* argv[])
             mif->match (mparams, a, tgs, diag, true /* progress */);
 
           if (dump_match)
-            dump (a);
+            dump (*ctx, a);
 
           if (mif->execute != nullptr && !ops.match_only ())
             mif->execute (mparams, a, tgs, diag, true /* progress */);
@@ -1613,7 +1617,7 @@ main (int argc, char* argv[])
           if (mif->operation_pre != nullptr)
             mif->operation_pre (mparams, post_oid); // Cannot be translated.
 
-          set_current_oif (*post_oif, oif);
+          ctx->current_oif (*post_oif, oif);
 
           action a (mid, post_oid, oid);
 
@@ -1625,7 +1629,7 @@ main (int argc, char* argv[])
               mif->match (mparams, a, tgs, diag, true /* progress */);
 
             if (dump_match)
-              dump (a);
+              dump (*ctx, a);
 
             if (mif->execute != nullptr && !ops.match_only ())
               mif->execute (mparams, a, tgs, diag, true /* progress */);
diff --git a/build2/bin/init.cxx b/build2/bin/init.cxx
index b46d643..4e80834 100644
--- a/build2/bin/init.cxx
+++ b/build2/bin/init.cxx
@@ -56,7 +56,7 @@ namespace build2
       // Target is a string and not target_triplet because it can be
       // specified by the user.
       //
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       vp.insert<string>    ("config.bin.target",   true);
       vp.insert<string>    ("config.bin.pattern",  true);
@@ -266,7 +266,7 @@ namespace build2
         // config.bin.target
         //
         {
-          const variable& var (var_pool["config.bin.target"]);
+          const variable& var (rs.ctx.var_pool["config.bin.target"]);
 
           // We first see if the value was specified via the configuration
           // mechanism.
@@ -343,7 +343,7 @@ namespace build2
         // config.bin.pattern
         //
         {
-          const variable& var (var_pool["config.bin.pattern"]);
+          const variable& var (rs.ctx.var_pool["config.bin.pattern"]);
 
           // We first see if the value was specified via the configuration
           // mechanism.
@@ -568,7 +568,7 @@ namespace build2
       //
       if (first)
       {
-        auto& v (var_pool.rw (rs));
+        auto& v (rs.ctx.var_pool.rw (rs));
 
         v.insert<process_path> ("bin.ar.path");
         v.insert<process_path> ("bin.ranlib.path");
@@ -744,7 +744,7 @@ namespace build2
       //
       if (first)
       {
-        auto& v (var_pool.rw (rs));
+        auto& v (rs.ctx.var_pool.rw (rs));
 
         v.insert<process_path> ("bin.ld.path");
         v.insert<path>         ("config.bin.ld", true);
@@ -857,7 +857,7 @@ namespace build2
       //
       if (first)
       {
-        auto& v (var_pool.rw (rs));
+        auto& v (rs.ctx.var_pool.rw (rs));
 
         v.insert<process_path> ("bin.rc.path");
         v.insert<path>         ("config.bin.rc", true);
diff --git a/build2/bin/target.cxx b/build2/bin/target.cxx
index ec4a0ef..2ef3d87 100644
--- a/build2/bin/target.cxx
+++ b/build2/bin/target.cxx
@@ -88,11 +88,12 @@ namespace build2
     //
     template <typename M, typename G>
     static target*
-    m_factory (const target_type&, dir_path dir, dir_path out, string n)
+    m_factory (context& ctx,
+               const target_type&, dir_path dir, dir_path out, string n)
     {
-      const G* g (targets.find<G> (dir, out, n));
+      const G* g (ctx.targets.find<G> (dir, out, n));
 
-      M* m (new M (move (dir), move (out), move (n)));
+      M* m (new M (ctx, move (dir), move (out), move (n)));
       m->group = g;
 
       return m;
@@ -258,21 +259,22 @@ namespace build2
     //
     template <typename G, typename E, typename A, typename S>
     static target*
-    g_factory (const target_type&, dir_path dir, dir_path out, string n)
+    g_factory (context& ctx,
+               const target_type&, dir_path dir, dir_path out, string n)
     {
       // Casts are MT-aware (during serial load).
       //
       E* e (phase == run_phase::load
-            ? const_cast<E*> (targets.find<E> (dir, out, n))
+            ? const_cast<E*> (ctx.targets.find<E> (dir, out, n))
             : nullptr);
       A* a (phase == run_phase::load
-            ? const_cast<A*> (targets.find<A> (dir, out, n))
+            ? const_cast<A*> (ctx.targets.find<A> (dir, out, n))
             : nullptr);
       S* s (phase == run_phase::load
-            ? const_cast<S*> (targets.find<S> (dir, out, n))
+            ? const_cast<S*> (ctx.targets.find<S> (dir, out, n))
             : nullptr);
 
-      G* g (new G (move (dir), move (out), move (n)));
+      G* g (new G (ctx, move (dir), move (out), move (n)));
 
       if (e != nullptr) e->group = g;
       if (a != nullptr) a->group = g;
@@ -323,16 +325,17 @@ namespace build2
     // The same as g_factory() but without E.
     //
     static target*
-    libul_factory (const target_type&, dir_path dir, dir_path out, string n)
+    libul_factory (context& ctx,
+                   const target_type&, dir_path dir, dir_path out, string n)
     {
       libua* a (phase == run_phase::load
-                ? const_cast<libua*> (targets.find<libua> (dir, out, n))
+                ? const_cast<libua*> (ctx.targets.find<libua> (dir, out, n))
                 : nullptr);
       libus* s (phase == run_phase::load
-                ? const_cast<libus*> (targets.find<libus> (dir, out, n))
+                ? const_cast<libus*> (ctx.targets.find<libus> (dir, out, n))
                 : nullptr);
 
-      libul* g (new libul (move (dir), move (out), move (n)));
+      libul* g (new libul (ctx, move (dir), move (out), move (n)));
 
       if (a != nullptr) a->group = g;
       if (s != nullptr) s->group = g;
@@ -403,18 +406,19 @@ namespace build2
     }
 
     static target*
-    lib_factory (const target_type&, dir_path dir, dir_path out, string n)
+    lib_factory (context& ctx,
+                 const target_type&, dir_path dir, dir_path out, string n)
     {
       // Casts are MT-aware (during serial load).
       //
       liba* a (phase == run_phase::load
-               ? const_cast<liba*> (targets.find<liba> (dir, out, n))
+               ? const_cast<liba*> (ctx.targets.find<liba> (dir, out, n))
                : nullptr);
       libs* s (phase == run_phase::load
-               ? const_cast<libs*> (targets.find<libs> (dir, out, n))
+               ? const_cast<libs*> (ctx.targets.find<libs> (dir, out, n))
                : nullptr);
 
-      lib* l (new lib (move (dir), move (out), move (n)));
+      lib* l (new lib (ctx, move (dir), move (out), move (n)));
 
       if (a != nullptr) a->group = l;
       if (s != nullptr) s->group = l;
diff --git a/build2/c/init.cxx b/build2/c/init.cxx
index 5c55281..ff9cc58 100644
--- a/build2/c/init.cxx
+++ b/build2/c/init.cxx
@@ -145,7 +145,7 @@ namespace build2
 
       // Enter all the variables and initialize the module data.
       //
-      auto& v (var_pool.rw (rs));
+      auto& v (rs.ctx.var_pool.rw (rs));
 
       cc::config_data d {
         cc::lang::c,
diff --git a/build2/cc/common.cxx b/build2/cc/common.cxx
index aa0eb89..4f5db4c 100644
--- a/build2/cc/common.cxx
+++ b/build2/cc/common.cxx
@@ -87,7 +87,7 @@ namespace build2
       bool impl (proc_impl && proc_impl (l, la));
       bool cc (false), same (false);
 
-      auto& vp (var_pool);
+      auto& vp (top_bs.ctx.var_pool);
       lookup c_e_libs;
       lookup x_e_libs;
 
@@ -221,7 +221,7 @@ namespace build2
         : &cast<dir_paths> (
           bs.root_scope ()->vars[same
                                  ? x_sys_lib_dirs
-                                 : var_pool[*t + ".sys_lib_dirs"]]);
+                                 : bs.ctx.var_pool[*t + ".sys_lib_dirs"]]);
       };
 
       auto find_linfo = [top_li, t, cc, &bs, &l, &li] ()
@@ -474,7 +474,7 @@ namespace build2
         if (xt == nullptr)
         {
           if (n.qualified ())
-            xt = import_existing (pk);
+            xt = import_existing (s.ctx, pk);
         }
 
         if (xt == nullptr)
@@ -494,20 +494,21 @@ namespace build2
     //
     template <typename T>
     ulock common::
-    insert_library (T*& r,
+    insert_library (context& ctx,
+                    T*& r,
                     const string& name,
                     const dir_path& d,
                     optional<string> ext,
                     bool exist,
                     tracer& trace)
     {
-      auto p (targets.insert_locked (T::static_type,
-                                     d,
-                                     dir_path (),
-                                     name,
-                                     move (ext),
-                                     true, // Implied.
-                                     trace));
+      auto p (ctx.targets.insert_locked (T::static_type,
+                                         d,
+                                         dir_path (),
+                                         name,
+                                         move (ext),
+                                         true, // Implied.
+                                         trace));
 
       assert (!exist || !p.second.owns_lock ());
       r = &p.first.template as<T> ();
@@ -626,6 +627,8 @@ namespace build2
                     &name, ext,
                     &p, &f, exist, &trace, this] (const dir_path& d) -> bool
       {
+        context& ctx (p.scope->ctx);
+
         timestamp mt;
 
         // libs
@@ -648,9 +651,10 @@ namespace build2
             if (tclass == "windows")
             {
               libi* i (nullptr);
-              insert_library (i, name, d, se, exist, trace);
+              insert_library (ctx, i, name, d, se, exist, trace);
 
-              ulock l (insert_library (s, name, d, nullopt, exist, trace));
+              ulock l (
+                insert_library (ctx, s, name, d, nullopt, exist, trace));
 
               if (!exist)
               {
@@ -677,7 +681,7 @@ namespace build2
             }
             else
             {
-              insert_library (s, name, d, se, exist, trace);
+              insert_library (ctx, s, name, d, se, exist, trace);
 
               s->mtime (mt);
               s->path (move (f));
@@ -697,7 +701,7 @@ namespace build2
 
             if (mt != timestamp_nonexistent)
             {
-              insert_library (s, name, d, se, exist, trace);
+              insert_library (ctx, s, name, d, se, exist, trace);
 
               s->mtime (mt);
               s->path (move (f));
@@ -722,7 +726,7 @@ namespace build2
             // Note that this target is outside any project which we treat
             // as out trees.
             //
-            insert_library (a, name, d, ae, exist, trace);
+            insert_library (ctx, a, name, d, ae, exist, trace);
             a->mtime (mt);
             a->path (move (f));
           }
@@ -760,14 +764,14 @@ namespace build2
 
             if (na && !r.first.empty ())
             {
-              insert_library (a, name, d, nullopt, exist, trace);
+              insert_library (ctx, a, name, d, nullopt, exist, trace);
               a->mtime (timestamp_unreal);
               a->path (empty_path);
             }
 
             if (ns && !r.second.empty ())
             {
-              insert_library (s, name, d, nullopt, exist, trace);
+              insert_library (ctx, s, name, d, nullopt, exist, trace);
               s->mtime (timestamp_unreal);
               s->path (empty_path);
             }
@@ -821,7 +825,8 @@ namespace build2
       // Enter (or find) the lib{} target group.
       //
       lib* lt;
-      insert_library (lt, name, *pd, l ? p.tk.ext : nullopt, exist, trace);
+      insert_library (
+        p.scope->ctx, lt, name, *pd, l ? p.tk.ext : nullopt, exist, trace);
 
       // Result.
       //
diff --git a/build2/cc/common.hxx b/build2/cc/common.hxx
index c58a7f3..b24eb7d 100644
--- a/build2/cc/common.hxx
+++ b/build2/cc/common.hxx
@@ -8,6 +8,7 @@
 #include <libbuild2/types.hxx>
 #include <libbuild2/utility.hxx>
 
+#include <libbuild2/context.hxx>
 #include <libbuild2/variable.hxx>
 
 #include <build2/bin/target.hxx>
@@ -278,7 +279,8 @@ namespace build2
 
       template <typename T>
       static ulock
-      insert_library (T*&,
+      insert_library (context&,
+                      T*&,
                       const string&,
                       const dir_path&,
                       optional<string>,
diff --git a/build2/cc/compile-rule.cxx b/build2/cc/compile-rule.cxx
index 833fd44..9dede21 100644
--- a/build2/cc/compile-rule.cxx
+++ b/build2/cc/compile-rule.cxx
@@ -365,7 +365,9 @@ namespace build2
         const variable& var (
           com
           ? c_export_poptions
-          : (t == x ? x_export_poptions : var_pool[t + ".export.poptions"]));
+          : (t == x
+             ? x_export_poptions
+             : l.ctx.var_pool[t + ".export.poptions"]));
 
         append_options (args, l, var);
       };
@@ -418,7 +420,9 @@ namespace build2
         const variable& var (
           com
           ? c_export_poptions
-          : (t == x ? x_export_poptions : var_pool[t + ".export.poptions"]));
+          : (t == x
+             ? x_export_poptions
+             : l.ctx.var_pool[t + ".export.poptions"]));
 
         hash_options (cs, l, var);
       };
@@ -472,7 +476,9 @@ namespace build2
         const variable& var (
           com
           ? c_export_poptions
-          : (t == x ? x_export_poptions : var_pool[t + ".export.poptions"]));
+          : (t == x
+             ? x_export_poptions
+             : l.ctx.var_pool[t + ".export.poptions"]));
 
         append_prefixes (m, l, var);
       };
@@ -2161,7 +2167,7 @@ namespace build2
         //
         small_vector<const target_type*, 2> tts;
 
-        const scope& bs (scopes.find (d));
+        const scope& bs (t.ctx.scopes.find (d));
         if (const scope* rs = bs.root_scope ())
         {
           tts = map_extension (bs, n, e);
@@ -2201,7 +2207,7 @@ namespace build2
           // absolute path with a spelled-out extension to multiple targets.
           //
           for (const target_type* tt: tts)
-            if ((r = targets.find (*tt, d, out, n, e, trace)) != nullptr)
+            if ((r = t.ctx.targets.find (*tt, d, out, n, e, trace)) != nullptr)
               break;
 
           // Note: we can't do this because of the in-source builds where
@@ -2887,7 +2893,7 @@ namespace build2
                     // See if this path is inside a project with an out-of-
                     // tree build and is in the out directory tree.
                     //
-                    const scope& bs (scopes.find (d));
+                    const scope& bs (t.ctx.scopes.find (d));
                     if (bs.root_scope () != nullptr)
                     {
                       const dir_path& bp (bs.out_path ());
@@ -5101,7 +5107,7 @@ namespace build2
                    modules_sidebuild_dir /=
                    x);
 
-      const scope* ps (&scopes.find (pd));
+      const scope* ps (&rs.ctx.scopes.find (pd));
 
       if (ps->out_path () != pd)
       {
@@ -5112,7 +5118,7 @@ namespace build2
         // Re-test again now that we are in exclusive phase (another thread
         // could have already created and loaded the subproject).
         //
-        ps = &scopes.find (pd);
+        ps = &rs.ctx.scopes.find (pd);
 
         if (ps->out_path () != pd)
         {
@@ -5200,7 +5206,7 @@ namespace build2
       // exists then we assume all this is already done (otherwise why would
       // someone have created such a target).
       //
-      if (const file* bt = targets.find<file> (
+      if (const file* bt = bs.ctx.targets.find<file> (
             tt,
             pd,
             dir_path (), // Always in the out tree.
@@ -5237,13 +5243,14 @@ namespace build2
         }
       }
 
-      auto p (targets.insert_locked (tt,
-                                     move (pd),
-                                     dir_path (), // Always in the out tree.
-                                     move (mf),
-                                     nullopt,     // Use default extension.
-                                     true,        // Implied.
-                                     trace));
+      auto p (bs.ctx.targets.insert_locked (
+                tt,
+                move (pd),
+                dir_path (), // Always in the out tree.
+                move (mf),
+                nullopt,     // Use default extension.
+                true,        // Implied.
+                trace));
       file& bt (static_cast<file&> (p.first));
 
       // Note that this is racy and someone might have created this target
@@ -5295,7 +5302,7 @@ namespace build2
 
       const target_type& tt (compile_types (li.type).hbmi);
 
-      if (const file* bt = targets.find<file> (
+      if (const file* bt = bs.ctx.targets.find<file> (
             tt,
             pd,
             dir_path (), // Always in the out tree.
@@ -5307,13 +5314,14 @@ namespace build2
       prerequisites ps;
       ps.push_back (prerequisite (ht));
 
-      auto p (targets.insert_locked (tt,
-                                     move (pd),
-                                     dir_path (), // Always in the out tree.
-                                     move (mf),
-                                     nullopt,     // Use default extension.
-                                     true,        // Implied.
-                                     trace));
+      auto p (bs.ctx.targets.insert_locked (
+                tt,
+                move (pd),
+                dir_path (), // Always in the out tree.
+                move (mf),
+                nullopt,     // Use default extension.
+                true,        // Implied.
+                trace));
       file& bt (static_cast<file&> (p.first));
 
       // Note that this is racy and someone might have created this target
diff --git a/build2/cc/init.cxx b/build2/cc/init.cxx
index e22ece7..3ff59a1 100644
--- a/build2/cc/init.cxx
+++ b/build2/cc/init.cxx
@@ -77,7 +77,7 @@ namespace build2
 
       // Enter variables. Note: some overridable, some not.
       //
-      auto& v (var_pool.rw (rs));
+      auto& v (rs.ctx.var_pool.rw (rs));
 
       auto v_t (variable_visibility::target);
 
@@ -276,7 +276,8 @@ namespace build2
         // Prepare configuration hints. They are only used on the first load
         // of bin.config so we only populate them on our first load.
         //
-        variable_map h;
+        variable_map h (rs.ctx);
+
         if (first)
         {
           // Note that all these variables have already been registered.
diff --git a/build2/cc/link-rule.cxx b/build2/cc/link-rule.cxx
index bb91722..09109c2 100644
--- a/build2/cc/link-rule.cxx
+++ b/build2/cc/link-rule.cxx
@@ -165,14 +165,15 @@ namespace build2
                 // otherwise the above search would have returned the member
                 // target.
                 //
-                pt = search_existing (p.prerequisite.key (tt));
+                pt = search_existing (t.ctx, p.prerequisite.key (tt));
               }
             }
             else if (!p.is_a<libue> ())
             {
               // See if we also/instead have a group.
               //
-              pg = search_existing (p.prerequisite.key (libul::static_type));
+              pg = search_existing (t.ctx,
+                                    p.prerequisite.key (libul::static_type));
 
               if (pt == nullptr)
                 swap (pt, pg);
@@ -1163,7 +1164,7 @@ namespace build2
           bool u;
           if ((u = pt->is_a<libux> ()) || pt->is_a<liba> ())
           {
-            const variable& var (var_pool["bin.whole"]); // @@ Cache.
+            const variable& var (t.ctx.var_pool["bin.whole"]); // @@ Cache.
 
             // See the bin module for the lookup semantics discussion. Note
             // that the variable is not overridable so we omit find_override()
@@ -1473,7 +1474,7 @@ namespace build2
             ? (exp ? c_export_loptions : c_loptions)
             : (t == x
                ? (exp ? x_export_loptions : x_loptions)
-               : var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
+               : l.ctx.var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
 
           append_options (d.args, *g, var);
         }
@@ -1575,7 +1576,7 @@ namespace build2
             ? (exp ? c_export_loptions : c_loptions)
             : (t == x
                ? (exp ? x_export_loptions : x_loptions)
-               : var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
+               : l.ctx.var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
 
           hash_options (d.cs, *g, var);
         }
@@ -1966,7 +1967,7 @@ namespace build2
         const string& cs (
           cast<string> (
             rs[tsys == "win32-msvc"
-               ? var_pool["bin.ld.checksum"]
+               ? t.ctx.var_pool["bin.ld.checksum"]
                : x_checksum]));
 
         if (dd.expect (cs) != nullptr)
diff --git a/build2/cc/module.cxx b/build2/cc/module.cxx
index 36cdd1a..064d954 100644
--- a/build2/cc/module.cxx
+++ b/build2/cc/module.cxx
@@ -41,9 +41,13 @@ namespace build2
 
       config::save_module (rs, x, 250);
 
-      const variable& config_c_poptions (var_pool["config.cc.poptions"]);
-      const variable& config_c_coptions (var_pool["config.cc.coptions"]);
-      const variable& config_c_loptions (var_pool["config.cc.loptions"]);
+      auto& vp (rs.ctx.var_pool.rw (rs));
+
+      // Must already exist.
+      //
+      const variable& config_c_poptions (vp["config.cc.poptions"]);
+      const variable& config_c_coptions (vp["config.cc.coptions"]);
+      const variable& config_c_loptions (vp["config.cc.loptions"]);
 
       // config.x
       //
@@ -63,8 +67,6 @@ namespace build2
         //
         if (!cc_loaded)
         {
-          auto& vp (var_pool.rw (rs));
-
           for (const char* const* pm (x_hinters); *pm != nullptr; ++pm)
           {
             string m (*pm);
@@ -201,7 +203,7 @@ namespace build2
       {
         // Prepare configuration hints.
         //
-        variable_map h;
+        variable_map h (rs.ctx);
 
         // Note that all these variables have already been registered.
         //
@@ -545,7 +547,7 @@ namespace build2
       //
       if (!cast_false<bool> (rs["cc.core.config.loaded"]))
       {
-        variable_map h;
+        variable_map h (rs.ctx);
 
         if (!ci.bin_pattern.empty ())
           h.assign ("config.bin.pattern") = ci.bin_pattern;
diff --git a/build2/cc/msvc.cxx b/build2/cc/msvc.cxx
index 6125fdd..7d8c3f5 100644
--- a/build2/cc/msvc.cxx
+++ b/build2/cc/msvc.cxx
@@ -365,6 +365,7 @@ namespace build2
     {
       // Pretty similar logic to search_library().
       //
+      assert (p.scope != nullptr);
 
       const optional<string>& ext (p.tk.ext);
       const string& name (*p.tk.name);
@@ -403,7 +404,7 @@ namespace build2
         // Enter the target.
         //
         T* t;
-        common::insert_library (t, name, d, e, exist, trace);
+        common::insert_library (p.scope->ctx, t, name, d, e, exist, trace);
 
         t->mtime (mt);
         t->path (move (f));
@@ -453,6 +454,8 @@ namespace build2
     {
       tracer trace (x, "msvc_search_shared");
 
+      assert (pk.scope != nullptr);
+
       libs* s (nullptr);
 
       auto search = [&s, &ld, &d, &pk, exist, &trace] (
@@ -461,7 +464,9 @@ namespace build2
         if (libi* i = msvc_search_library<libi> (
               ld, d, pk, otype::s, pf, sf, exist, trace))
         {
-          ulock l (insert_library (s, *pk.tk.name, d, nullopt, exist, trace));
+          ulock l (
+            insert_library (
+              pk.scope->ctx, s, *pk.tk.name, d, nullopt, exist, trace));
 
           if (!exist)
           {
diff --git a/build2/cc/pkgconfig.cxx b/build2/cc/pkgconfig.cxx
index c23b746..13cc752 100644
--- a/build2/cc/pkgconfig.cxx
+++ b/build2/cc/pkgconfig.cxx
@@ -1027,7 +1027,7 @@ namespace build2
 
       // Parse modules and add them to the prerequisites.
       //
-      auto parse_modules = [&trace, &next, this]
+      auto parse_modules = [&trace, &next, &s, this]
         (const pkgconf& pc, prerequisites& ps)
       {
         string mstr (pc.variable ("cxx_modules"));
@@ -1057,7 +1057,7 @@ namespace build2
           // For now there are only C++ modules.
           //
           auto tl (
-            targets.insert_locked (
+            s.ctx.targets.insert_locked (
               *x_mod,
               mp.directory (),
               dir_path (),
diff --git a/build2/cc/utility.cxx b/build2/cc/utility.cxx
index 3271f7c..ff807c9 100644
--- a/build2/cc/utility.cxx
+++ b/build2/cc/utility.cxx
@@ -72,7 +72,7 @@ namespace build2
         //
         return phase == run_phase::match && !exist
           ? &search (x, tt, x.dir, x.out, x.name)
-          : search_existing (tt, x.dir, x.out, x.name);
+          : search_existing (x.ctx, tt, x.dir, x.out, x.name);
       }
       else
       {
diff --git a/build2/cli/init.cxx b/build2/cli/init.cxx
index 6d20aa0..2e553f7 100644
--- a/build2/cli/init.cxx
+++ b/build2/cli/init.cxx
@@ -43,7 +43,7 @@ namespace build2
       //
       if (first)
       {
-        auto& v (var_pool.rw (rs));
+        auto& v (rs.ctx.var_pool.rw (rs));
 
         // Note: some overridable, some not.
         //
diff --git a/build2/cli/rule.cxx b/build2/cli/rule.cxx
index f6bebee..f6c0763 100644
--- a/build2/cli/rule.cxx
+++ b/build2/cli/rule.cxx
@@ -112,7 +112,7 @@ namespace build2
 
         // Check if there is a corresponding cli.cxx{} group.
         //
-        const cli_cxx* g (targets.find<cli_cxx> (t.dir, t.out, t.name));
+        const cli_cxx* g (t.ctx.targets.find<cli_cxx> (t.dir, t.out, t.name));
 
         // If not or if it has no prerequisites (happens when we use it to
         // set cli.options) and this target has a cli{} prerequisite, then
@@ -124,7 +124,7 @@ namespace build2
                 prerequisite_members (a, t)))
           {
             if (g == nullptr)
-              g = &targets.insert<cli_cxx> (t.dir, t.out, t.name, trace);
+              g = &t.ctx.targets.insert<cli_cxx> (t.dir, t.out, t.name, trace);
 
             g->prerequisites (prerequisites {p->as_prerequisite ()});
           }
diff --git a/build2/cli/target.cxx b/build2/cli/target.cxx
index 096295a..caa12b0 100644
--- a/build2/cli/target.cxx
+++ b/build2/cli/target.cxx
@@ -45,7 +45,8 @@ namespace build2
     }
 
     static target*
-    cli_cxx_factory (const target_type&, dir_path d, dir_path o, string n)
+    cli_cxx_factory (context& ctx,
+                     const target_type&, dir_path d, dir_path o, string n)
     {
       tracer trace ("cli::cli_cxx_factory");
 
@@ -55,11 +56,11 @@ namespace build2
       //
       // Also required for the src-out remapping logic.
       //
-      targets.insert<cxx::hxx> (d, o, n, trace);
-      targets.insert<cxx::cxx> (d, o, n, trace);
-      targets.insert<cxx::ixx> (d, o, n, trace);
+      ctx.targets.insert<cxx::hxx> (d, o, n, trace);
+      ctx.targets.insert<cxx::cxx> (d, o, n, trace);
+      ctx.targets.insert<cxx::ixx> (d, o, n, trace);
 
-      return new cli_cxx (move (d), move (o), move (n));
+      return new cli_cxx (ctx, move (d), move (o), move (n));
     }
 
     const target_type cli_cxx::static_type
diff --git a/build2/cxx/init.cxx b/build2/cxx/init.cxx
index c355763..1ffa098 100644
--- a/build2/cxx/init.cxx
+++ b/build2/cxx/init.cxx
@@ -62,7 +62,8 @@ namespace build2
       //
       auto enter = [&rs] (const char* v) -> const variable&
       {
-        return var_pool.rw (rs).insert<bool> (v, variable_visibility::project);
+        return rs.ctx.var_pool.rw (rs).insert<bool> (
+          v, variable_visibility::project);
       };
 
       // NOTE: see also module sidebuild subproject if changing anything about
@@ -370,7 +371,7 @@ namespace build2
 
       // Enter all the variables and initialize the module data.
       //
-      auto& v (var_pool.rw (rs));
+      auto& v (rs.ctx.var_pool.rw (rs));
 
       cc::config_data d {
         cc::lang::cxx,
@@ -572,7 +573,7 @@ namespace build2
 
       config_module& cm (*rs.lookup_module<config_module> ("cxx.guess"));
 
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       bool modules (cast<bool> (rs["cxx.features.modules"]));
 
diff --git a/libbuild2/algorithm.cxx b/libbuild2/algorithm.cxx
index 50db5d3..298f945 100644
--- a/libbuild2/algorithm.cxx
+++ b/libbuild2/algorithm.cxx
@@ -41,7 +41,7 @@ namespace build2
 
     if (r == nullptr)
     {
-      r = search_existing (p.key ());
+      r = search_existing (p.scope.ctx, p.key ());
 
       if (r != nullptr)
         search_custom (p, *r);
@@ -59,20 +59,22 @@ namespace build2
     // business.
     //
     if (pk.proj)
-      return import (pk);
+      return import (t.ctx, pk);
 
     if (const target* pt = pk.tk.type->search (t, pk))
       return *pt;
 
-    return create_new_target (pk);
+    return create_new_target (t.ctx, pk);
   }
 
   const target*
-  search_existing (const prerequisite_key& pk)
+  search_existing (context& ctx, const prerequisite_key& pk)
   {
     assert (phase == run_phase::match || phase == run_phase::execute);
 
-    return pk.proj ? import_existing (pk) : search_existing_target (pk);
+    return pk.proj
+      ? import_existing (ctx, pk)
+      : search_existing_target (ctx, pk);
   }
 
   const target&
@@ -130,7 +132,9 @@ namespace build2
     prerequisite_key pk {
       n.proj, {tt, &n.dir, q ? &empty_dir_path : &out, &n.value, ext}, &s};
 
-    return q ? import_existing (pk) : search_existing_target (pk);
+    return q
+      ? import_existing (s.ctx, pk)
+      : search_existing_target (s.ctx, pk);
   }
 
   // target_lock
@@ -266,13 +270,13 @@ namespace build2
 
     target& m (*mp != nullptr // Might already be there.
                ? **mp
-               : targets.insert (tt,
-                                 dir,
-                                 out,
-                                 move (n),
-                                 nullopt /* ext     */,
-                                 true    /* implied */,
-                                 trace).first);
+               : t.ctx.targets.insert (tt,
+                                       dir,
+                                       out,
+                                       move (n),
+                                       nullopt /* ext     */,
+                                       true    /* implied */,
+                                       trace).first);
     if (*mp == nullptr)
     {
       *mp = &m;
@@ -303,7 +307,7 @@ namespace build2
       //
       for (const scope* s (&bs);
            s != nullptr;
-           s = s->root () ? global_scope : s->parent_scope ())
+           s = s->root () ? &s->global_scope () : s->parent_scope ())
       {
         const operation_rule_map* om (s->rules[mo]);
 
@@ -897,7 +901,7 @@ namespace build2
     //
     const dir_path& d (parent && t.name.empty () ? t.dir.directory () : t.dir);
 
-    const scope& bs (scopes.find (d));
+    const scope& bs (t.ctx.scopes.find (d));
     const scope* rs (bs.root_scope ());
 
     // If root scope is NULL, then this can mean that we are out of any
@@ -973,7 +977,7 @@ namespace build2
 
       if (op_t != nullptr)
       {
-        op_s = &scopes.find (t.dir);
+        op_s = &t.ctx.scopes.find (t.dir);
 
         if (op_s->out_path () == t.dir && !op_s->operation_callbacks.empty ())
         {
@@ -1401,7 +1405,7 @@ namespace build2
     // stops at the project boundary).
     //
     if (!l.defined ())
-      l = global_scope->find (*var_backlink, t.key ());
+      l = t.ctx.global_scope.find (*var_backlink, t.key ());
 
     return l ? backlink_test (t, l) : nullopt;
   }
diff --git a/libbuild2/algorithm.hxx b/libbuild2/algorithm.hxx
index 4707ae7..2ca83e3 100644
--- a/libbuild2/algorithm.hxx
+++ b/libbuild2/algorithm.hxx
@@ -16,6 +16,7 @@
 namespace build2
 {
   class scope;
+  class context;
   class prerequisite;
   class prerequisite_key;
 
@@ -42,7 +43,7 @@ namespace build2
   search (const target&, const prerequisite_key&);
 
   LIBBUILD2_SYMEXPORT const target*
-  search_existing (const prerequisite_key&);
+  search_existing (context&, const prerequisite_key&);
 
   // Uniform search interface for prerequisite/prerequisite_member.
   //
@@ -61,7 +62,7 @@ namespace build2
   //
   const target&
   search (const target&,
-          const target_type& type,
+          const target_type&,
           const dir_path& dir,
           const dir_path& out,
           const string& name,
@@ -70,7 +71,8 @@ namespace build2
           const optional<project_name>& proj = nullopt);
 
   const target*
-  search_existing (const target_type& type,
+  search_existing (context&,
+                   const target_type&,
                    const dir_path& dir,
                    const dir_path& out,
                    const string& name,
diff --git a/libbuild2/algorithm.ixx b/libbuild2/algorithm.ixx
index 6bc771e..8bd69c9 100644
--- a/libbuild2/algorithm.ixx
+++ b/libbuild2/algorithm.ixx
@@ -57,7 +57,8 @@ namespace build2
   }
 
   inline const target*
-  search_existing (const target_type& type,
+  search_existing (context& ctx,
+                   const target_type& type,
                    const dir_path& dir,
                    const dir_path& out,
                    const string& name,
@@ -66,6 +67,7 @@ namespace build2
                    const optional<project_name>& proj)
   {
     return search_existing (
+      ctx,
       prerequisite_key {
         proj,
         {
diff --git a/libbuild2/bash/rule.cxx b/libbuild2/bash/rule.cxx
index d9bf857..2f2de2d 100644
--- a/libbuild2/bash/rule.cxx
+++ b/libbuild2/bash/rule.cxx
@@ -157,13 +157,13 @@ namespace build2
 
                 if (mt != timestamp_nonexistent)
                 {
-                  auto rp (targets.insert_locked (bash::static_type,
-                                                  ap.directory (),
-                                                  dir_path () /* out */,
-                                                  p.name,
-                                                  ext,
-                                                  true /* implied */,
-                                                  trace));
+                  auto rp (t.ctx.targets.insert_locked (bash::static_type,
+                                                        ap.directory (),
+                                                        dir_path () /* out */,
+                                                        p.name,
+                                                        ext,
+                                                        true /* implied */,
+                                                        trace));
 
                   bash& pt (rp.first.as<bash> ());
 
@@ -281,7 +281,7 @@ namespace build2
               continue;
           }
 
-          if (const scope* rs = scopes.find (b->dir).root_scope ())
+          if (const scope* rs = t.ctx.scopes.find (b->dir).root_scope ())
           {
             const dir_path& d (pp.sub (rs->src_path ())
                                ? rs->src_path ()
diff --git a/libbuild2/config/init.cxx b/libbuild2/config/init.cxx
index b790569..9bdfef9 100644
--- a/libbuild2/config/init.cxx
+++ b/libbuild2/config/init.cxx
@@ -80,7 +80,7 @@ namespace build2
 
       assert (config_hints.empty ()); // We don't known any hints.
 
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       // Load config.build if one exists (we don't need to worry about
       // disfigure since we will never be init'ed).
@@ -103,7 +103,7 @@ namespace build2
           {
             // Assume missing version is 0.
             //
-            auto p (extract_variable (f, c_v));
+            auto p (extract_variable (rs.ctx, f, c_v));
             uint64_t v (p.second ? cast<uint64_t> (p.first) : 0);
 
             if (v != module::version)
@@ -126,7 +126,7 @@ namespace build2
       // global scope similar to builtin rules.
       //
       {
-        auto& r (rs.global ().rules);
+        auto& r (rs.global_scope ().rules);
         r.insert<mtime_target> (
           configure_id, 0, "config.file", file_rule::instance);
       }
diff --git a/libbuild2/config/operation.cxx b/libbuild2/config/operation.cxx
index c3ce4b7..e235a3a 100644
--- a/libbuild2/config/operation.cxx
+++ b/libbuild2/config/operation.cxx
@@ -28,12 +28,12 @@ namespace build2
     // configure
     //
     static void
-    save_src_root (const scope& root)
+    save_src_root (const scope& rs)
     {
-      const dir_path& out_root (root.out_path ());
-      const dir_path& src_root (root.src_path ());
+      const dir_path& out_root (rs.out_path ());
+      const dir_path& src_root (rs.src_path ());
 
-      path f (out_root / root.root_extra->src_root_file);
+      path f (out_root / rs.root_extra->src_root_file);
 
       if (verb >= 2)
         text << "cat >" << f;
@@ -57,12 +57,12 @@ namespace build2
     }
 
     static void
-    save_out_root (const scope& root)
+    save_out_root (const scope& rs)
     {
-      const dir_path& out_root (root.out_path ());
-      const dir_path& src_root (root.src_path ());
+      const dir_path& out_root (rs.out_path ());
+      const dir_path& src_root (rs.src_path ());
 
-      path f (src_root / root.root_extra->out_root_file);
+      path f (src_root / rs.root_extra->out_root_file);
 
       if (verb)
         text << (verb >= 2 ? "cat >" : "save ") << f;
@@ -88,14 +88,14 @@ namespace build2
     using project_set = set<const scope*>; // Use pointers to get comparison.
 
     static void
-    save_config (const scope& root, const project_set& projects)
+    save_config (const scope& rs, const project_set& projects)
     {
-      path f (config_file (root));
+      path f (config_file (rs));
 
       if (verb)
         text << (verb >= 2 ? "cat >" : "save ") << f;
 
-      const module& mod (*root.lookup_module<const module> (module::name));
+      const module& mod (*rs.lookup_module<const module> (module::name));
 
       try
       {
@@ -107,7 +107,7 @@ namespace build2
 
         ofs << "config.version = " << module::version << endl;
 
-        if (auto l = root.vars[var_amalgamation])
+        if (auto l = rs.vars[var_amalgamation])
         {
           const dir_path& d (cast<dir_path> (l));
 
@@ -130,10 +130,10 @@ namespace build2
           {
             const variable& var (sv.var);
 
-            pair<lookup, size_t> org (root.find_original (var));
+            pair<lookup, size_t> org (rs.find_original (var));
             pair<lookup, size_t> ovr (var.overrides == nullptr
                                       ? org
-                                      : root.find_override (var, org));
+                                      : rs.find_override (var, org));
             const lookup& l (ovr.first);
 
             // We definitely write values that are set on our root scope or
@@ -144,7 +144,7 @@ namespace build2
             if (!l.defined ())
               continue;
 
-            if (!(l.belongs (root) || l.belongs (*global_scope)))
+            if (!(l.belongs (rs) || l.belongs (rs.ctx.global_scope)))
             {
               // This is presumably an inherited value. But it could also be
               // some left-over garbage. For example, an amalgamation could
@@ -162,7 +162,7 @@ namespace build2
               // root.
               //
               bool found (false);
-              const scope* r (&root);
+              const scope* r (&rs);
               while ((r = r->parent_scope ()->root_scope ()) != nullptr)
               {
                 if (l.belongs (*r))
@@ -307,14 +307,14 @@ namespace build2
     }
 
     static void
-    configure_project (action a, const scope& root, project_set& projects)
+    configure_project (action a, const scope& rs, project_set& projects)
     {
       tracer trace ("configure_project");
 
-      const dir_path& out_root (root.out_path ());
-      const dir_path& src_root (root.src_path ());
+      const dir_path& out_root (rs.out_path ());
+      const dir_path& src_root (rs.src_path ());
 
-      if (!projects.insert (&root).second)
+      if (!projects.insert (&rs).second)
       {
         l5 ([&]{trace << "skipping already configured " << out_root;});
         return;
@@ -324,8 +324,8 @@ namespace build2
       //
       if (out_root != src_root)
       {
-        mkdir_p (out_root / root.root_extra->build_dir);
-        mkdir (out_root / root.root_extra->bootstrap_dir, 2);
+        mkdir_p (out_root / rs.root_extra->build_dir);
+        mkdir (out_root / rs.root_extra->bootstrap_dir, 2);
       }
 
       // We distinguish between a complete configure and operation-
@@ -338,11 +338,11 @@ namespace build2
         // Save src-root.build unless out_root is the same as src.
         //
         if (out_root != src_root)
-          save_src_root (root);
+          save_src_root (rs);
 
         // Save config.build.
         //
-        save_config (root, projects);
+        save_config (rs, projects);
       }
       else
       {
@@ -350,54 +350,54 @@ namespace build2
 
       // Configure subprojects that have been loaded.
       //
-      if (auto l = root.vars[var_subprojects])
+      if (auto l = rs.vars[var_subprojects])
       {
         for (auto p: cast<subprojects> (l))
         {
           const dir_path& pd (p.second);
           dir_path out_nroot (out_root / pd);
-          const scope& nroot (scopes.find (out_nroot));
+          const scope& nrs (rs.ctx.scopes.find (out_nroot));
 
           // @@ Strictly speaking we need to check whether the config
           // module was loaded for this subproject.
           //
-          if (nroot.out_path () != out_nroot) // This subproject not loaded.
+          if (nrs.out_path () != out_nroot) // This subproject not loaded.
             continue;
 
-          configure_project (a, nroot, projects);
+          configure_project (a, nrs, projects);
         }
       }
     }
 
     static void
-    configure_forward (const scope& root, project_set& projects)
+    configure_forward (const scope& rs, project_set& projects)
     {
       tracer trace ("configure_forward");
 
-      const dir_path& out_root (root.out_path ());
-      const dir_path& src_root (root.src_path ());
+      const dir_path& out_root (rs.out_path ());
+      const dir_path& src_root (rs.src_path ());
 
-      if (!projects.insert (&root).second)
+      if (!projects.insert (&rs).second)
       {
         l5 ([&]{trace << "skipping already configured " << src_root;});
         return;
       }
 
-      mkdir (src_root / root.root_extra->bootstrap_dir, 2); // Make sure exists.
-      save_out_root (root);
+      mkdir (src_root / rs.root_extra->bootstrap_dir, 2); // Make sure exists.
+      save_out_root (rs);
 
       // Configure subprojects. Since we don't load buildfiles if configuring
       // a forward, we do it for all known subprojects.
       //
-      if (auto l = root.vars[var_subprojects])
+      if (auto l = rs.vars[var_subprojects])
       {
         for (auto p: cast<subprojects> (l))
         {
           dir_path out_nroot (out_root / p.second);
-          const scope& nroot (scopes.find (out_nroot));
-          assert (nroot.out_path () == out_nroot);
+          const scope& nrs (rs.ctx.scopes.find (out_nroot));
+          assert (nrs.out_path () == out_nroot);
 
-          configure_forward (nroot, projects);
+          configure_forward (nrs, projects);
         }
       }
     }
@@ -451,7 +451,7 @@ namespace build2
 
     static void
     configure_load (const values& params,
-                    scope& root,
+                    scope& rs,
                     const path& buildfile,
                     const dir_path& out_base,
                     const dir_path& src_base,
@@ -463,19 +463,19 @@ namespace build2
         // forwarding but in order to configure subprojects we have to
         // bootstrap them (similar to disfigure).
         //
-        create_bootstrap_inner (root);
+        create_bootstrap_inner (rs);
 
-        if (root.out_path () == root.src_path ())
-          fail (l) << "forwarding to source directory " << root.src_path ();
+        if (rs.out_path () == rs.src_path ())
+          fail (l) << "forwarding to source directory " << rs.src_path ();
       }
       else
-        load (params, root, buildfile, out_base, src_base, l); // Normal load.
+        load (params, rs, buildfile, out_base, src_base, l); // Normal load.
     }
 
     static void
     configure_search (const values& params,
-                      const scope& root,
-                      const scope& base,
+                      const scope& rs,
+                      const scope& bs,
                       const path& bf,
                       const target_key& tk,
                       const location& l,
@@ -486,10 +486,10 @@ namespace build2
         // For forwarding we only collect the projects (again, similar to
         // disfigure).
         //
-        ts.push_back (&root);
+        ts.push_back (&rs);
       }
       else
-        search (params, root, base, bf, tk, l, ts); // Normal search.
+        search (params, rs, bs, bf, tk, l, ts); // Normal search.
     }
 
     static void
@@ -515,8 +515,8 @@ namespace build2
         {
           // Forward configuration.
           //
-          const scope& root (*static_cast<const scope*> (at.target));
-          configure_forward (root, projects);
+          const scope& rs (*static_cast<const scope*> (at.target));
+          configure_forward (rs, projects);
           continue;
         }
 
@@ -552,7 +552,7 @@ namespace build2
             if (oif->id != id)
               continue;
 
-            set_current_oif (*oif);
+            rs->ctx.current_oif (*oif);
 
             phase_lock pl (run_phase::match);
             match (action (configure_id, id), t);
@@ -586,14 +586,14 @@ namespace build2
     //
 
     static bool
-    disfigure_project (action a, const scope& root, project_set& projects)
+    disfigure_project (action a, const scope& rs, project_set& projects)
     {
       tracer trace ("disfigure_project");
 
-      const dir_path& out_root (root.out_path ());
-      const dir_path& src_root (root.src_path ());
+      const dir_path& out_root (rs.out_path ());
+      const dir_path& src_root (rs.src_path ());
 
-      if (!projects.insert (&root).second)
+      if (!projects.insert (&rs).second)
       {
         l5 ([&]{trace << "skipping already disfigured " << out_root;});
         return false;
@@ -604,16 +604,16 @@ namespace build2
       // Disfigure subprojects. Since we don't load buildfiles during
       // disfigure, we do it for all known subprojects.
       //
-      if (auto l = root.vars[var_subprojects])
+      if (auto l = rs.vars[var_subprojects])
       {
         for (auto p: cast<subprojects> (l))
         {
           const dir_path& pd (p.second);
           dir_path out_nroot (out_root / pd);
-          const scope& nroot (scopes.find (out_nroot));
-          assert (nroot.out_path () == out_nroot); // See disfigure_load().
+          const scope& nrs (rs.ctx.scopes.find (out_nroot));
+          assert (nrs.out_path () == out_nroot); // See disfigure_load().
 
-          r = disfigure_project (a, nroot, projects) || r;
+          r = disfigure_project (a, nrs, projects) || r;
 
           // We use mkdir_p() to create the out_root of a subproject
           // which means there could be empty parent directories left
@@ -643,19 +643,19 @@ namespace build2
       {
         l5 ([&]{trace << "completely disfiguring " << out_root;});
 
-        r = rmfile (config_file (root)) || r;
+        r = rmfile (config_file (rs)) || r;
 
         if (out_root != src_root)
         {
-          r = rmfile (out_root / root.root_extra->src_root_file, 2) || r;
+          r = rmfile (out_root / rs.root_extra->src_root_file, 2) || r;
 
           // Clean up the directories.
           //
           // Note: try to remove the root/ hooks directory if it is empty.
           //
-          r = rmdir (out_root / root.root_extra->root_dir,      2) || r;
-          r = rmdir (out_root / root.root_extra->bootstrap_dir, 2) || r;
-          r = rmdir (out_root / root.root_extra->build_dir,     2) || r;
+          r = rmdir (out_root / rs.root_extra->root_dir,      2) || r;
+          r = rmdir (out_root / rs.root_extra->bootstrap_dir, 2) || r;
+          r = rmdir (out_root / rs.root_extra->build_dir,     2) || r;
 
           switch (rmdir (out_root))
           {
@@ -687,16 +687,16 @@ namespace build2
     }
 
     static bool
-    disfigure_forward (const scope& root, project_set& projects)
+    disfigure_forward (const scope& rs, project_set& projects)
     {
       // Pretty similar logic to disfigure_project().
       //
       tracer trace ("disfigure_forward");
 
-      const dir_path& out_root (root.out_path ());
-      const dir_path& src_root (root.src_path ());
+      const dir_path& out_root (rs.out_path ());
+      const dir_path& src_root (rs.src_path ());
 
-      if (!projects.insert (&root).second)
+      if (!projects.insert (&rs).second)
       {
         l5 ([&]{trace << "skipping already disfigured " << src_root;});
         return false;
@@ -704,23 +704,23 @@ namespace build2
 
       bool r (false);
 
-      if (auto l = root.vars[var_subprojects])
+      if (auto l = rs.vars[var_subprojects])
       {
         for (auto p: cast<subprojects> (l))
         {
           dir_path out_nroot (out_root / p.second);
-          const scope& nroot (scopes.find (out_nroot));
-          assert (nroot.out_path () == out_nroot);
+          const scope& nrs (rs.ctx.scopes.find (out_nroot));
+          assert (nrs.out_path () == out_nroot);
 
-          r = disfigure_forward (nroot, projects) || r;
+          r = disfigure_forward (nrs, projects) || r;
         }
       }
 
       // Remove the out-root.build file and try to remove the bootstrap/
       // directory if it is empty.
       //
-      r = rmfile (src_root / root.root_extra->out_root_file)    || r;
-      r = rmdir  (src_root / root.root_extra->bootstrap_dir, 2) || r;
+      r = rmfile (src_root / rs.root_extra->out_root_file)    || r;
+      r = rmdir  (src_root / rs.root_extra->bootstrap_dir, 2) || r;
 
       return r;
     }
@@ -757,14 +757,14 @@ namespace build2
 
     static void
     disfigure_search (const values&,
-                      const scope& root,
+                      const scope& rs,
                       const scope&,
                       const path&,
                       const target_key&,
                       const location&,
                       action_targets& ts)
     {
-      ts.push_back (&root);
+      ts.push_back (&rs);
     }
 
     static void
@@ -790,23 +790,23 @@ namespace build2
       //
       for (const action_target& at: ts)
       {
-        const scope& root (*static_cast<const scope*> (at.target));
+        const scope& rs (*static_cast<const scope*> (at.target));
 
         if (!(fwd
-              ? disfigure_forward (   root, projects)
-              : disfigure_project (a, root, projects)))
+              ? disfigure_forward (   rs, projects)
+              : disfigure_project (a, rs, projects)))
         {
           // Create a dir{$out_root/} target to signify the project's root in
           // diagnostics. Not very clean but seems harmless.
           //
           target& t (
-            targets.insert (dir::static_type,
-                            fwd ? root.src_path () : root.out_path (),
-                            dir_path (), // Out tree.
-                            "",
-                            nullopt,
-                            true,       // Implied.
-                            trace).first);
+            rs.ctx.targets.insert (dir::static_type,
+                                   fwd ? rs.src_path () : rs.out_path (),
+                                   dir_path (), // Out tree.
+                                   "",
+                                   nullopt,
+                                   true,       // Implied.
+                                   trace).first);
 
           if (verb != 0 && diag >= 2)
             info << diag_done (a, t);
@@ -836,7 +836,7 @@ namespace build2
     // create
     //
     static void
-    save_config (const dir_path& d, const variable_overrides& var_ovs)
+    save_config (context& ctx, const dir_path& d)
     {
       // Since there aren't any sub-projects yet, any config.import.* values
       // that the user may want to specify won't be saved in config.build. So
@@ -846,13 +846,13 @@ namespace build2
       // going to do is bootstrap the newly created project, similar to the
       // way main() does it.
       //
-      scope& gs (*scope::global_);
+      scope& gs (ctx.global_scope.rw ());
       scope& rs (load_project (gs, d, d, false /* fwd */, false /* load */));
       module& m (*rs.lookup_module<module> (module::name));
 
       // Save all the global config.import.* variables.
       //
-      variable_pool& vp (var_pool.rw (rs));
+      variable_pool& vp (ctx.var_pool.rw (rs));
       for (auto p (gs.vars.find_namespace (vp.insert ("config.import")));
            p.first != p.second;
            ++p.first)
@@ -869,7 +869,7 @@ namespace build2
       // Now project-specific. For now we just save all of them and let
       // save_config() above weed out the ones that don't apply.
       //
-      for (const variable_override& vo: var_ovs)
+      for (const variable_override& vo: ctx.var_overrides)
       {
         const variable& var (vo.var);
 
@@ -879,7 +879,7 @@ namespace build2
     }
 
     const string&
-    preprocess_create (const variable_overrides& var_ovs,
+    preprocess_create (context& ctx,
                        values& params,
                        vector_view<opspec>& spec,
                        bool lifted,
@@ -986,7 +986,7 @@ namespace build2
                           true,        /* buildfile */
                           "the create meta-operation");
 
-          save_config (d, var_ovs);
+          save_config (ctx, d);
         }
       }
 
diff --git a/libbuild2/config/operation.hxx b/libbuild2/config/operation.hxx
index 0a88f96..8b2a29d 100644
--- a/libbuild2/config/operation.hxx
+++ b/libbuild2/config/operation.hxx
@@ -18,7 +18,7 @@ namespace build2
     extern const meta_operation_info mo_disfigure;
 
     const string&
-    preprocess_create (const variable_overrides&,
+    preprocess_create (context&,
                        values&,
                        vector_view<opspec>&,
                        bool,
diff --git a/libbuild2/config/utility.cxx b/libbuild2/config/utility.cxx
index 746639d..a89fac6 100644
--- a/libbuild2/config/utility.cxx
+++ b/libbuild2/config/utility.cxx
@@ -75,7 +75,7 @@ namespace build2
       // any original values, they will be "visible"; see find_override() for
       // details.
       //
-      const variable& vns (var_pool.rw (r).insert ("config." + n));
+      const variable& vns (r.ctx.var_pool.rw (r).insert ("config." + n));
       for (scope* s (&r); s != nullptr; s = s->parent_scope ())
       {
         for (auto p (s->vars.find_namespace (vns));
@@ -101,7 +101,7 @@ namespace build2
       // Pattern-typed in boot() as bool.
       //
       const variable& var (
-        var_pool.rw (rs).insert ("config." + n + ".configured"));
+        rs.ctx.var_pool.rw (rs).insert ("config." + n + ".configured"));
 
       if (current_mif->id == configure_id)
         save_variable (rs, var);
@@ -116,7 +116,7 @@ namespace build2
       // Pattern-typed in boot() as bool.
       //
       const variable& var (
-        var_pool.rw (rs).insert ("config." + n + ".configured"));
+        rs.ctx.var_pool.rw (rs).insert ("config." + n + ".configured"));
 
       if (current_mif->id == configure_id)
         save_variable (rs, var);
diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index a063693..b1995b6 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -58,7 +58,7 @@ namespace build2
               uint64_t save_flags = 0)
     {
       return required (
-        root, var_pool[name], default_value, override, save_flags);
+        root, root.ctx.var_pool[name], default_value, override, save_flags);
     }
 
     inline pair<lookup, bool>
@@ -86,7 +86,7 @@ namespace build2
     inline pair<lookup, bool>
     omitted (scope& root, const string& name)
     {
-      return omitted (root, var_pool[name]);
+      return omitted (root, root.ctx.var_pool[name]);
     }
 
     // Set, if necessary, an optional config.* variable. In particular, an
@@ -105,7 +105,7 @@ namespace build2
     inline lookup
     optional (scope& root, const string& name)
     {
-      return optional (root, var_pool[name]);
+      return optional (root, root.ctx.var_pool[name]);
     }
 
     // Check whether there are any variables specified from the config
diff --git a/libbuild2/context.cxx b/libbuild2/context.cxx
index 1cc8bbc..720e8d8 100644
--- a/libbuild2/context.cxx
+++ b/libbuild2/context.cxx
@@ -10,6 +10,8 @@
 #include <libbuild2/rule.hxx>
 #include <libbuild2/scope.hxx>
 #include <libbuild2/target.hxx>
+#include <libbuild2/variable.hxx>
+#include <libbuild2/operation.hxx>
 #include <libbuild2/diagnostics.hxx>
 
 #include <libbutl/ft/exception.hxx> // uncaught_exceptions
@@ -25,379 +27,48 @@ using namespace butl;
 
 namespace build2
 {
-  scheduler sched;
-
-  run_phase phase;
-  run_phase_mutex phase_mutex;
-
-  size_t load_generation;
-
-  bool run_phase_mutex::
-  lock (run_phase p)
-  {
-    bool r;
-
-    {
-      mlock l (m_);
-      bool u (lc_ == 0 && mc_ == 0 && ec_ == 0); // Unlocked.
-
-      // Increment the counter.
-      //
-      condition_variable* v (nullptr);
-      switch (p)
-      {
-      case run_phase::load:    lc_++; v = &lv_; break;
-      case run_phase::match:   mc_++; v = &mv_; break;
-      case run_phase::execute: ec_++; v = &ev_; break;
-      }
-
-      // If unlocked, switch directly to the new phase. Otherwise wait for the
-      // phase switch. Note that in the unlocked case we don't need to notify
-      // since there is nobody waiting (all counters are zero).
-      //
-      if (u)
-      {
-        phase = p;
-        r = !fail_;
-      }
-      else if (phase != p)
-      {
-        sched.deactivate (false /* external */);
-        for (; phase != p; v->wait (l)) ;
-        r = !fail_;
-        l.unlock (); // Important: activate() can block.
-        sched.activate (false /* external */);
-      }
-      else
-        r = !fail_;
-    }
-
-    // In case of load, acquire the exclusive access mutex.
-    //
-    if (p == run_phase::load)
-    {
-      lm_.lock ();
-      r = !fail_; // Re-query.
-    }
-
-    return r;
-  }
-
-  void run_phase_mutex::
-  unlock (run_phase p)
-  {
-    // In case of load, release the exclusive access mutex.
-    //
-    if (p == run_phase::load)
-      lm_.unlock ();
-
-    {
-      mlock l (m_);
-
-      // Decrement the counter and see if this phase has become unlocked.
-      //
-      bool u (false);
-      switch (p)
-      {
-      case run_phase::load:    u = (--lc_ == 0); break;
-      case run_phase::match:   u = (--mc_ == 0); break;
-      case run_phase::execute: u = (--ec_ == 0); break;
-      }
-
-      // If the phase is unlocked, pick a new phase and notify the waiters.
-      // Note that we notify all load waiters so that they can all serialize
-      // behind the second-level mutex.
-      //
-      if (u)
-      {
-        condition_variable* v;
-
-        if      (lc_ != 0) {phase = run_phase::load;    v = &lv_;}
-        else if (mc_ != 0) {phase = run_phase::match;   v = &mv_;}
-        else if (ec_ != 0) {phase = run_phase::execute; v = &ev_;}
-        else               {phase = run_phase::load;    v = nullptr;}
-
-        if (v != nullptr)
-        {
-          l.unlock ();
-          v->notify_all ();
-        }
-      }
-    }
-  }
-
-  bool run_phase_mutex::
-  relock (run_phase o, run_phase n)
-  {
-    // Pretty much a fused unlock/lock implementation except that we always
-    // switch into the new phase.
-    //
-    assert (o != n);
-
-    bool r;
-
-    if (o == run_phase::load)
-      lm_.unlock ();
-
-    {
-      mlock l (m_);
-      bool u (false);
-
-      switch (o)
-      {
-      case run_phase::load:    u = (--lc_ == 0); break;
-      case run_phase::match:   u = (--mc_ == 0); break;
-      case run_phase::execute: u = (--ec_ == 0); break;
-      }
-
-      // Set if will be waiting or notifying others.
-      //
-      condition_variable* v (nullptr);
-      switch (n)
-      {
-      case run_phase::load:    v = lc_++ != 0 || !u ? &lv_ : nullptr; break;
-      case run_phase::match:   v = mc_++ != 0 || !u ? &mv_ : nullptr; break;
-      case run_phase::execute: v = ec_++ != 0 || !u ? &ev_ : nullptr; break;
-      }
-
-      if (u)
-      {
-        phase = n;
-        r = !fail_;
-
-        // Notify others that could be waiting for this phase.
-        //
-        if (v != nullptr)
-        {
-          l.unlock ();
-          v->notify_all ();
-        }
-      }
-      else // phase != n
-      {
-        sched.deactivate (false /* external */);
-        for (; phase != n; v->wait (l)) ;
-        r = !fail_;
-        l.unlock (); // Important: activate() can block.
-        sched.activate (false /* external */);
-      }
-    }
-
-    if (n == run_phase::load)
-    {
-      lm_.lock ();
-      r = !fail_; // Re-query.
-    }
-
-    return r;
-  }
-
-  // C++17 deprecated uncaught_exception() so use uncaught_exceptions() if
-  // available.
+  // Create global scope. Note that the empty path is a prefix for any other
+  // path. See the comment in <libbutl/prefix-map.mxx> for details.
   //
-  static inline bool
-  uncaught_exception ()
+  static inline scope&
+  create_global_scope (scope_map& m)
   {
-#ifdef __cpp_lib_uncaught_exceptions
-    return std::uncaught_exceptions () != 0;
-#else
-    return std::uncaught_exception ();
-#endif
-  }
-
-  // phase_lock
-  //
-  static
-#ifdef __cpp_thread_local
-  thread_local
-#else
-  __thread
-#endif
-  phase_lock* phase_lock_instance;
-
-  phase_lock::
-  phase_lock (run_phase p)
-      : p (p)
-  {
-    if (phase_lock* l = phase_lock_instance)
-      assert (l->p == p);
-    else
-    {
-      if (!phase_mutex.lock (p))
-      {
-        phase_mutex.unlock (p);
-        throw failed ();
-      }
-
-      phase_lock_instance = this;
-
-      //text << this_thread::get_id () << " phase acquire " << p;
-    }
-  }
-
-  phase_lock::
-  ~phase_lock ()
-  {
-    if (phase_lock_instance == this)
-    {
-      phase_lock_instance = nullptr;
-      phase_mutex.unlock (p);
-
-      //text << this_thread::get_id () << " phase release " << p;
-    }
-  }
-
-  // phase_unlock
-  //
-  phase_unlock::
-  phase_unlock (bool u)
-      : l (u ? phase_lock_instance : nullptr)
-  {
-    if (u)
-    {
-      phase_lock_instance = nullptr;
-      phase_mutex.unlock (l->p);
-
-      //text << this_thread::get_id () << " phase unlock  " << l->p;
-    }
-  }
-
-  phase_unlock::
-  ~phase_unlock () noexcept (false)
-  {
-    if (l != nullptr)
-    {
-      bool r (phase_mutex.lock (l->p));
-      phase_lock_instance = l;
-
-      // Fail unless we are already failing. Note that we keep the phase
-      // locked since there will be phase_lock down the stack to unlock it.
-      //
-      if (!r && !uncaught_exception ())
-        throw failed ();
-
-      //text << this_thread::get_id () << " phase lock    " << l->p;
-    }
-  }
-
-  // phase_switch
-  //
-  phase_switch::
-  phase_switch (run_phase n)
-      : o (phase), n (n)
-  {
-    if (!phase_mutex.relock (o, n))
-    {
-      phase_mutex.relock (n, o);
-      throw failed ();
-    }
-
-    phase_lock_instance->p = n;
-
-    if (n == run_phase::load) // Note: load lock is exclusive.
-      load_generation++;
-
-    //text << this_thread::get_id () << " phase switch  " << o << " " << n;
-  }
-
-  phase_switch::
-  ~phase_switch () noexcept (false)
-  {
-    // If we are coming off a failed load phase, mark the phase_mutex as
-    // failed to terminate all other threads since the build state may no
-    // longer be valid.
-    //
-    if (n == run_phase::load && uncaught_exception ())
-    {
-      mlock l (phase_mutex.m_);
-      phase_mutex.fail_ = true;
-    }
-
-    bool r (phase_mutex.relock (n, o));
-    phase_lock_instance->p = o;
-
-    // Similar logic to ~phase_unlock().
-    //
-    if (!r && !uncaught_exception ())
-      throw failed ();
-
-    //text << this_thread::get_id () << " phase restore " << n << " " << o;
-  }
-
-  string current_mname;
-  string current_oname;
-
-  const meta_operation_info* current_mif;
-  const operation_info* current_inner_oif;
-  const operation_info* current_outer_oif;
-  size_t current_on;
-  execution_mode current_mode;
-  bool current_diag_noise;
-
-  atomic_count dependency_count;
-  atomic_count target_count;
-  atomic_count skip_count;
-
-  bool keep_going = false;
-  bool dry_run = false;
-
-  void
-  set_current_mif (const meta_operation_info& mif)
-  {
-    if (current_mname != mif.name)
-    {
-      current_mname = mif.name;
-      global_scope->rw ().assign (var_build_meta_operation) = mif.name;
-    }
-
-    current_mif = &mif;
-    current_on = 0; // Reset.
-  }
+    auto i (m.insert (dir_path ()));
+    scope& r (i->second);
+    r.out_path_ = &i->first;
+    return r;
+  };
 
-  void
-  set_current_oif (const operation_info& inner_oif,
-                   const operation_info* outer_oif,
-                   bool diag_noise)
+  struct context::data
   {
-    current_oname = (outer_oif == nullptr ? inner_oif : *outer_oif).name;
-    current_inner_oif = &inner_oif;
-    current_outer_oif = outer_oif;
-    current_on++;
-    current_mode = inner_oif.mode;
-    current_diag_noise = diag_noise;
-
-    // Reset counters (serial execution).
-    //
-    dependency_count.store (0, memory_order_relaxed);
-    target_count.store (0, memory_order_relaxed);
-    skip_count.store (0, memory_order_relaxed);
-  }
-
-  variable_overrides
-  reset (const strings& cmd_vars)
+    scope_map scopes;
+    target_set targets;
+    variable_pool var_pool;
+    variable_overrides var_overrides;
+
+    data (context& c): scopes (c), targets (c), var_pool (true /* global */) {}
+  };
+
+  context::
+  context (scheduler& s, const strings& cmd_vars)
+      : data_ (new data (*this)),
+        sched (s),
+        scopes (data_->scopes),
+        global_scope (create_global_scope (data_->scopes)),
+        targets (data_->targets),
+        var_pool (data_->var_pool),
+        var_overrides (data_->var_overrides)
   {
-    tracer trace ("reset");
-
-    // @@ Do we want to unload dynamically loaded modules? Note that this will
-    //    be purely an optimization since a module could be linked-in (i.e., a
-    //    module cannot expect to be unloaded/re-initialized for each meta-
-    //    operation).
+    tracer trace ("context");
 
-    l6 ([&]{trace << "resetting build state";});
+    l6 ([&]{trace << "initializing build state";});
 
-    auto& vp (variable_pool::instance);
-    auto& sm (scope_map::instance);
+    scope_map& sm (data_->scopes);
+    variable_pool& vp (data_->var_pool);
 
-    variable_overrides vos;
-
-    targets.clear ();
-    sm.clear ();
-    vp.clear ();
-
-    // Reset meta/operation tables. Note that the order should match the id
-    // constants in <libbuild2/operation.hxx>.
+    // Initialize the meta/operation tables. Note that the order should match
+    // the id constants in <libbuild2/operation.hxx>.
     //
-    meta_operation_table.clear ();
     meta_operation_table.insert ("noop");
     meta_operation_table.insert ("perform");
     meta_operation_table.insert ("configure");
@@ -420,23 +91,10 @@ namespace build2
     operation_table.insert ("uninstall");
     operation_table.insert ("update-for-install");
 
-    // Create global scope. Note that the empty path is a prefix for any other
-    // path. See the comment in <libbutl/prefix-map.mxx> for details.
-    //
-    auto make_global_scope = [] () -> scope&
-    {
-      auto i (scope_map::instance.insert (dir_path ()));
-      scope& r (i->second);
-      r.out_path_ = &i->first;
-      global_scope = scope::global_ = &r;
-      return r;
-    };
-
-    scope& gs (make_global_scope ());
-
     // Setup the global scope before parsing any variable overrides since they
     // may reference these things.
     //
+    scope& gs (global_scope.rw ());
 
     gs.assign<dir_path> ("build.work") = work;
     gs.assign<dir_path> ("build.home") = home;
@@ -458,10 +116,10 @@ namespace build2
     {
       const standard_version& v (build_version);
 
-      auto set = [&gs] (const char* var, auto val)
+      auto set = [&gs, &vp] (const char* var, auto val)
       {
         using T = decltype (val);
-        gs.assign (variable_pool::instance.insert<T> (var)) = move (val);
+        gs.assign (vp.insert<T> (var)) = move (val);
       };
 
       // Note: here we assume epoch will always be 1 and therefore omit the
@@ -509,7 +167,7 @@ namespace build2
     // were built with. While it is not as precise (for example, a binary
     // built for i686 might be running on x86_64), it is good enough of an
     // approximation/fallback since most of the time we are interested in just
-    // the target class (e.g., linux, windows, macosx).
+    // the target class (e.g., linux, windows, macos).
     //
     {
       // Did the user ask us to use config.guess?
@@ -739,7 +397,7 @@ namespace build2
       // things simple. Pass original variable for diagnostics. Use current
       // working directory as pattern base.
       //
-      parser p;
+      parser p (*this);
       pair<value, token> r (p.parse_variable_value (l, gs, &work, var));
 
       if (r.second.type != token_type::eos)
@@ -752,8 +410,7 @@ namespace build2
         fail << "typed override of variable " << n;
 
       // Global and absolute scope overrides we can enter directly. Project
-      // and relative scope ones will be entered by the caller for each
-      // amalgamation/project.
+      // and relative scope ones will be entered later for each project.
       //
       if (c == '!' || (dir && dir->absolute ()))
       {
@@ -766,7 +423,7 @@ namespace build2
         v = move (r.first);
       }
       else
-        vos.push_back (
+        data_->var_overrides.push_back (
           variable_override {var, *o, move (dir), move (r.first)});
     }
 
@@ -784,7 +441,7 @@ namespace build2
     vp.insert_pattern<path> (
       "config.import.**", true, variable_visibility::normal, true);
 
-    // module.cxx:load_module().
+    // module.cxx:boot/init_module().
     //
     {
       auto v_p (variable_visibility::project);
@@ -847,13 +504,365 @@ namespace build2
       r.insert<mtime_target> (perform_update_id, "file", file_rule::instance);
       r.insert<mtime_target> (perform_clean_id, "file", file_rule::instance);
     }
+  }
+
+  context::
+  ~context ()
+  {
+    // Cannot be inline since context::data is undefined.
+  }
+
+  void context::
+  current_mif (const meta_operation_info& mif)
+  {
+    if (current_mname != mif.name)
+    {
+      current_mname = mif.name;
+      global_scope.rw ().assign (var_build_meta_operation) = mif.name;
+    }
+
+    build2::current_mif = &mif;
+    current_on = 0; // Reset.
+  }
+
+  void context::
+  current_oif (const operation_info& inner_oif,
+               const operation_info* outer_oif,
+               bool diag_noise)
+  {
+    current_oname = (outer_oif == nullptr ? inner_oif : *outer_oif).name;
+    current_inner_oif = &inner_oif;
+    current_outer_oif = outer_oif;
+    current_on++;
+    current_mode = inner_oif.mode;
+    current_diag_noise = diag_noise;
+
+    // Reset counters (serial execution).
+    //
+    dependency_count.store (0, memory_order_relaxed);
+    target_count.store (0, memory_order_relaxed);
+    skip_count.store (0, memory_order_relaxed);
+  }
+
+  scheduler sched;
+
+  run_phase phase;
+  run_phase_mutex phase_mutex;
+
+  size_t load_generation;
+
+  bool run_phase_mutex::
+  lock (run_phase p)
+  {
+    bool r;
+
+    {
+      mlock l (m_);
+      bool u (lc_ == 0 && mc_ == 0 && ec_ == 0); // Unlocked.
+
+      // Increment the counter.
+      //
+      condition_variable* v (nullptr);
+      switch (p)
+      {
+      case run_phase::load:    lc_++; v = &lv_; break;
+      case run_phase::match:   mc_++; v = &mv_; break;
+      case run_phase::execute: ec_++; v = &ev_; break;
+      }
+
+      // If unlocked, switch directly to the new phase. Otherwise wait for the
+      // phase switch. Note that in the unlocked case we don't need to notify
+      // since there is nobody waiting (all counters are zero).
+      //
+      if (u)
+      {
+        phase = p;
+        r = !fail_;
+      }
+      else if (phase != p)
+      {
+        sched.deactivate (false /* external */);
+        for (; phase != p; v->wait (l)) ;
+        r = !fail_;
+        l.unlock (); // Important: activate() can block.
+        sched.activate (false /* external */);
+      }
+      else
+        r = !fail_;
+    }
+
+    // In case of load, acquire the exclusive access mutex.
+    //
+    if (p == run_phase::load)
+    {
+      lm_.lock ();
+      r = !fail_; // Re-query.
+    }
+
+    return r;
+  }
+
+  void run_phase_mutex::
+  unlock (run_phase p)
+  {
+    // In case of load, release the exclusive access mutex.
+    //
+    if (p == run_phase::load)
+      lm_.unlock ();
+
+    {
+      mlock l (m_);
+
+      // Decrement the counter and see if this phase has become unlocked.
+      //
+      bool u (false);
+      switch (p)
+      {
+      case run_phase::load:    u = (--lc_ == 0); break;
+      case run_phase::match:   u = (--mc_ == 0); break;
+      case run_phase::execute: u = (--ec_ == 0); break;
+      }
 
-    return vos;
+      // If the phase is unlocked, pick a new phase and notify the waiters.
+      // Note that we notify all load waiters so that they can all serialize
+      // behind the second-level mutex.
+      //
+      if (u)
+      {
+        condition_variable* v;
+
+        if      (lc_ != 0) {phase = run_phase::load;    v = &lv_;}
+        else if (mc_ != 0) {phase = run_phase::match;   v = &mv_;}
+        else if (ec_ != 0) {phase = run_phase::execute; v = &ev_;}
+        else               {phase = run_phase::load;    v = nullptr;}
+
+        if (v != nullptr)
+        {
+          l.unlock ();
+          v->notify_all ();
+        }
+      }
+    }
   }
 
+  bool run_phase_mutex::
+  relock (run_phase o, run_phase n)
+  {
+    // Pretty much a fused unlock/lock implementation except that we always
+    // switch into the new phase.
+    //
+    assert (o != n);
+
+    bool r;
+
+    if (o == run_phase::load)
+      lm_.unlock ();
+
+    {
+      mlock l (m_);
+      bool u (false);
+
+      switch (o)
+      {
+      case run_phase::load:    u = (--lc_ == 0); break;
+      case run_phase::match:   u = (--mc_ == 0); break;
+      case run_phase::execute: u = (--ec_ == 0); break;
+      }
+
+      // Set if will be waiting or notifying others.
+      //
+      condition_variable* v (nullptr);
+      switch (n)
+      {
+      case run_phase::load:    v = lc_++ != 0 || !u ? &lv_ : nullptr; break;
+      case run_phase::match:   v = mc_++ != 0 || !u ? &mv_ : nullptr; break;
+      case run_phase::execute: v = ec_++ != 0 || !u ? &ev_ : nullptr; break;
+      }
+
+      if (u)
+      {
+        phase = n;
+        r = !fail_;
+
+        // Notify others that could be waiting for this phase.
+        //
+        if (v != nullptr)
+        {
+          l.unlock ();
+          v->notify_all ();
+        }
+      }
+      else // phase != n
+      {
+        sched.deactivate (false /* external */);
+        for (; phase != n; v->wait (l)) ;
+        r = !fail_;
+        l.unlock (); // Important: activate() can block.
+        sched.activate (false /* external */);
+      }
+    }
+
+    if (n == run_phase::load)
+    {
+      lm_.lock ();
+      r = !fail_; // Re-query.
+    }
+
+    return r;
+  }
+
+  // C++17 deprecated uncaught_exception() so use uncaught_exceptions() if
+  // available.
+  //
+  static inline bool
+  uncaught_exception ()
+  {
+#ifdef __cpp_lib_uncaught_exceptions
+    return std::uncaught_exceptions () != 0;
+#else
+    return std::uncaught_exception ();
+#endif
+  }
+
+  // phase_lock
+  //
+  static
+#ifdef __cpp_thread_local
+  thread_local
+#else
+  __thread
+#endif
+  phase_lock* phase_lock_instance;
+
+  phase_lock::
+  phase_lock (run_phase p)
+      : p (p)
+  {
+    if (phase_lock* l = phase_lock_instance)
+      assert (l->p == p);
+    else
+    {
+      if (!phase_mutex.lock (p))
+      {
+        phase_mutex.unlock (p);
+        throw failed ();
+      }
+
+      phase_lock_instance = this;
+
+      //text << this_thread::get_id () << " phase acquire " << p;
+    }
+  }
+
+  phase_lock::
+  ~phase_lock ()
+  {
+    if (phase_lock_instance == this)
+    {
+      phase_lock_instance = nullptr;
+      phase_mutex.unlock (p);
+
+      //text << this_thread::get_id () << " phase release " << p;
+    }
+  }
+
+  // phase_unlock
+  //
+  phase_unlock::
+  phase_unlock (bool u)
+      : l (u ? phase_lock_instance : nullptr)
+  {
+    if (u)
+    {
+      phase_lock_instance = nullptr;
+      phase_mutex.unlock (l->p);
+
+      //text << this_thread::get_id () << " phase unlock  " << l->p;
+    }
+  }
+
+  phase_unlock::
+  ~phase_unlock () noexcept (false)
+  {
+    if (l != nullptr)
+    {
+      bool r (phase_mutex.lock (l->p));
+      phase_lock_instance = l;
+
+      // Fail unless we are already failing. Note that we keep the phase
+      // locked since there will be phase_lock down the stack to unlock it.
+      //
+      if (!r && !uncaught_exception ())
+        throw failed ();
+
+      //text << this_thread::get_id () << " phase lock    " << l->p;
+    }
+  }
+
+  // phase_switch
+  //
+  phase_switch::
+  phase_switch (run_phase n)
+      : o (phase), n (n)
+  {
+    if (!phase_mutex.relock (o, n))
+    {
+      phase_mutex.relock (n, o);
+      throw failed ();
+    }
+
+    phase_lock_instance->p = n;
+
+    if (n == run_phase::load) // Note: load lock is exclusive.
+      load_generation++;
+
+    //text << this_thread::get_id () << " phase switch  " << o << " " << n;
+  }
+
+  phase_switch::
+  ~phase_switch () noexcept (false)
+  {
+    // If we are coming off a failed load phase, mark the phase_mutex as
+    // failed to terminate all other threads since the build state may no
+    // longer be valid.
+    //
+    if (n == run_phase::load && uncaught_exception ())
+    {
+      mlock l (phase_mutex.m_);
+      phase_mutex.fail_ = true;
+    }
+
+    bool r (phase_mutex.relock (n, o));
+    phase_lock_instance->p = o;
+
+    // Similar logic to ~phase_unlock().
+    //
+    if (!r && !uncaught_exception ())
+      throw failed ();
+
+    //text << this_thread::get_id () << " phase restore " << n << " " << o;
+  }
+
+  string current_mname;
+  string current_oname;
+
+  const meta_operation_info* current_mif;
+  const operation_info* current_inner_oif;
+  const operation_info* current_outer_oif;
+  size_t current_on;
+  execution_mode current_mode;
+  bool current_diag_noise;
+
+  atomic_count dependency_count;
+  atomic_count target_count;
+  atomic_count skip_count;
+
+  bool keep_going = false;
+  bool dry_run = false;
+
   void (*config_save_variable) (scope&, const variable&, uint64_t);
 
-  const string& (*config_preprocess_create) (const variable_overrides&,
+  const string& (*config_preprocess_create) (context&,
                                              values&,
                                              vector_view<opspec>&,
                                              bool,
diff --git a/libbuild2/context.hxx b/libbuild2/context.hxx
index ce9a996..f51645e 100644
--- a/libbuild2/context.hxx
+++ b/libbuild2/context.hxx
@@ -8,8 +8,11 @@
 #include <libbuild2/types.hxx>
 #include <libbuild2/utility.hxx>
 
-#include <libbuild2/variable.hxx>
-#include <libbuild2/operation.hxx>
+// NOTE: this file is included by pretty much every other "data model" header
+//       (scope, target, variable, etc) so including any of them here is
+//       probably a non-starter.
+//
+#include <libbuild2/action.hxx>
 #include <libbuild2/scheduler.hxx>
 
 #include <libbuild2/export.hxx>
@@ -17,11 +20,66 @@
 namespace build2
 {
   class scope;
+  class scope_map;
+  class target_set;
+
+  class variable;
+  class variable_pool;
+  struct variable_override;
+  using variable_overrides = vector<variable_override>;
+  class value;
+  using values = small_vector<value, 1>;
+
+  struct meta_operation_info;
+  struct operation_info;
+
+  struct opspec;
 
   // Main scheduler. Started up and shut down in main().
   //
+  // @@ CTX: move to main().
+  //
   LIBBUILD2_SYMEXPORT extern scheduler sched;
 
+  // @@ CTX: document (backlinks, non-overlap etc). RW story.
+  //
+  class LIBBUILD2_SYMEXPORT context
+  {
+    struct data;
+    unique_ptr<data> data_;
+
+  public:
+    scheduler& sched;
+
+    const scope_map& scopes;
+    const scope& global_scope;
+
+    target_set& targets;
+
+    const variable_pool& var_pool;
+    const variable_overrides& var_overrides; // Project and relative scope.
+
+  public:
+    explicit
+    context (scheduler&, const strings& cmd_vars = {});
+
+    void
+    current_mif (const meta_operation_info&);
+
+    void
+    current_oif (const operation_info& inner,
+                 const operation_info* outer = nullptr,
+                 bool diag_noise = true);
+
+    context (context&&) = delete;
+    context& operator= (context&&) = delete;
+
+    context (const context&) = delete;
+    context& operator= (const context&) = delete;
+
+    ~context ();
+  };
+
   // In order to perform each operation the build system goes through the
   // following phases:
   //
@@ -303,14 +361,6 @@ namespace build2
   LIBBUILD2_SYMEXPORT extern atomic_count target_count;
   LIBBUILD2_SYMEXPORT extern atomic_count skip_count;
 
-  LIBBUILD2_SYMEXPORT void
-  set_current_mif (const meta_operation_info&);
-
-  LIBBUILD2_SYMEXPORT void
-  set_current_oif (const operation_info& inner,
-                   const operation_info* outer = nullptr,
-                   bool diag_noise = true);
-
   // Keep going flag.
   //
   // Note that setting it to false is not of much help unless we are running
@@ -352,19 +402,13 @@ namespace build2
   //
   LIBBUILD2_SYMEXPORT extern bool dry_run;
 
-  // Reset the build state. In particular, this removes all the targets,
-  // scopes, and variables.
-  //
-  LIBBUILD2_SYMEXPORT variable_overrides
-  reset (const strings& cmd_vars);
-
   // Config module entry points.
   //
   LIBBUILD2_SYMEXPORT extern void (*config_save_variable) (
     scope&, const variable&, uint64_t flags);
 
   LIBBUILD2_SYMEXPORT extern const string& (*config_preprocess_create) (
-    const variable_overrides&,
+    context&,
     values&,
     vector_view<opspec>&,
     bool lifted,
diff --git a/libbuild2/dist/init.cxx b/libbuild2/dist/init.cxx
index 4729938..c6ffb67 100644
--- a/libbuild2/dist/init.cxx
+++ b/libbuild2/dist/init.cxx
@@ -37,7 +37,7 @@ namespace build2
       // Enter module variables. Do it during boot in case they get assigned
       // in bootstrap.build (which is customary for, e.g., dist.package).
       //
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       // Note: some overridable, some not.
       //
diff --git a/libbuild2/dist/operation.cxx b/libbuild2/dist/operation.cxx
index ac3912e..cdeb9ee 100644
--- a/libbuild2/dist/operation.cxx
+++ b/libbuild2/dist/operation.cxx
@@ -79,6 +79,8 @@ namespace build2
       if (rs == nullptr)
         fail << "out of project target " << t;
 
+      context& ctx (rs->ctx);
+
       const dir_path& out_root (rs->out_path ());
       const dir_path& src_root (rs->src_path ());
 
@@ -167,7 +169,7 @@ namespace build2
             if (operation_id pid = oif->pre (params, dist_id, loc))
             {
               const operation_info* poif (ops[pid]);
-              set_current_oif (*poif, oif, false /* diag_noise */);
+              ctx.current_oif (*poif, oif, false /* diag_noise */);
               action a (dist_id, poif->id, oif->id);
               match (params, a, ts,
                      1     /* diag (failures only) */,
@@ -175,7 +177,7 @@ namespace build2
             }
           }
 
-          set_current_oif (*oif, nullptr, false /* diag_noise */);
+          ctx.current_oif (*oif, nullptr, false /* diag_noise */);
           action a (dist_id, oif->id);
           match (params, a, ts,
                  1     /* diag (failures only) */,
@@ -186,7 +188,7 @@ namespace build2
             if (operation_id pid = oif->post (params, dist_id))
             {
               const operation_info* poif (ops[pid]);
-              set_current_oif (*poif, oif, false /* diag_noise */);
+              ctx.current_oif (*poif, oif, false /* diag_noise */);
               action a (dist_id, poif->id, oif->id);
               match (params, a, ts,
                      1     /* diag (failures only) */,
@@ -213,7 +215,7 @@ namespace build2
                         ? out_src (d, rs)
                         : dir_path ());
 
-          targets.insert<buildfile> (
+          rs.ctx.targets.insert<buildfile> (
             move (d),
             move (out),
             p.leaf ().base ().string (),
@@ -232,7 +234,7 @@ namespace build2
         {
           const dir_path& pd (p.second);
           dir_path out_nroot (out_root / pd);
-          const scope& nrs (scopes.find (out_nroot));
+          const scope& nrs (ctx.scopes.find (out_nroot));
 
           if (nrs.out_path () != out_nroot) // This subproject not loaded.
             continue;
@@ -251,9 +253,9 @@ namespace build2
       // distribute") since it will be useless (too fast).
       //
       action_targets files;
-      const variable& dist_var (var_pool["dist"]);
+      const variable& dist_var (ctx.var_pool["dist"]);
 
-      for (const auto& pt: targets)
+      for (const auto& pt: ctx.targets)
       {
         file* ft (pt->is_a<file> ());
 
@@ -305,13 +307,13 @@ namespace build2
         // Note also that we don't do any structured result printing.
         //
         size_t on (current_on);
-        set_current_mif (mo_perform);
+        ctx.current_mif (mo_perform);
         current_on = on + 1;
 
         if (mo_perform.operation_pre != nullptr)
           mo_perform.operation_pre (params, update_id);
 
-        set_current_oif (op_update, nullptr, false /* diag_noise */);
+        ctx.current_oif (op_update, nullptr, false /* diag_noise */);
 
         action a (perform_id, update_id);
 
@@ -374,7 +376,7 @@ namespace build2
             const dir_path& pd (p.second);
             if (dl.sub (pd))
             {
-              srs = &scopes.find (out_root / pd);
+              srs = &ctx.scopes.find (out_root / pd);
 
               if (auto* m = srs->lookup_module<module> (module::name))
                 cbs = &m->callbacks_;
diff --git a/libbuild2/dump.cxx b/libbuild2/dump.cxx
index 7d59891..27cd9e2 100644
--- a/libbuild2/dump.cxx
+++ b/libbuild2/dump.cxx
@@ -6,6 +6,7 @@
 
 #include <libbuild2/scope.hxx>
 #include <libbuild2/target.hxx>
+#include <libbuild2/context.hxx>
 #include <libbuild2/variable.hxx>
 #include <libbuild2/diagnostics.hxx>
 
@@ -400,7 +401,8 @@ namespace build2
 
     // Nested scopes of which we are an immediate parent.
     //
-    for (auto e (scopes.end ()); i != e && i->second.parent_scope () == &p;)
+    for (auto e (p.ctx.scopes.end ());
+         i != e && i->second.parent_scope () == &p; )
     {
       if (vb)
       {
@@ -421,7 +423,7 @@ namespace build2
     // Since targets can occupy multiple lines, we separate them with a
     // blank line.
     //
-    for (const auto& pt: targets)
+    for (const auto& pt: p.ctx.targets)
     {
       const target& t (*pt);
 
@@ -447,10 +449,10 @@ namespace build2
   }
 
   void
-  dump (optional<action> a)
+  dump (const context& c, optional<action> a)
   {
-    auto i (scopes.cbegin ());
-    assert (&i->second == global_scope);
+    auto i (c.scopes.cbegin ());
+    assert (&i->second == &c.global_scope);
 
     // We don't lock diag_stream here as dump() is supposed to be called from
     // the main thread prior/after to any other threads being spawned.
@@ -464,7 +466,7 @@ namespace build2
   void
   dump (const scope& s, const char* cind)
   {
-    const scope_map_base& m (scopes); // Iterator interface.
+    const scope_map_base& m (s.ctx.scopes); // Iterator interface.
     auto i (m.find (s.out_path ()));
     assert (i != m.end () && &i->second == &s);
 
diff --git a/libbuild2/dump.hxx b/libbuild2/dump.hxx
index fd1886b..aead805 100644
--- a/libbuild2/dump.hxx
+++ b/libbuild2/dump.hxx
@@ -16,13 +16,14 @@ namespace build2
 {
   class scope;
   class target;
+  class context;
 
   // Dump the build state to diag_stream. If action is specified, then assume
   // rules have been matched for this action and dump action-specific
   // information (like rule-specific variables).
   //
   LIBBUILD2_SYMEXPORT void
-  dump (optional<action> = nullopt);
+  dump (const context&, optional<action> = nullopt);
 
   LIBBUILD2_SYMEXPORT void
   dump (const scope&, const char* ind = "");
diff --git a/libbuild2/file.cxx b/libbuild2/file.cxx
index 1da9397..207f569 100644
--- a/libbuild2/file.cxx
+++ b/libbuild2/file.cxx
@@ -183,7 +183,7 @@ namespace build2
 
       l5 ([&]{trace << "sourcing " << bf;});
 
-      parser p (boot);
+      parser p (root.ctx, boot);
       p.parse_buildfile (is, bf, root, base);
     }
     catch (const io_error& e)
@@ -263,9 +263,9 @@ namespace build2
   }
 
   scope_map::iterator
-  create_root (scope& l, const dir_path& out_root, const dir_path& src_root)
+  create_root (scope& s, const dir_path& out_root, const dir_path& src_root)
   {
-    auto i (scopes.rw (l).insert (out_root, true /* root */));
+    auto i (s.ctx.scopes.rw (s).insert (out_root, true /* root */));
     scope& rs (i->second);
 
     // Set out_path. Note that src_path is set in setup_root() below.
@@ -373,7 +373,7 @@ namespace build2
     // First, enter the scope into the map and see if it is in any project. If
     // it is not, then there is nothing else to do.
     //
-    auto i (scopes.rw (root).insert (p));
+    auto i (root.ctx.scopes.rw (root).insert (p));
     scope& base (i->second);
     scope* rs (base.root_scope ());
 
@@ -410,7 +410,7 @@ namespace build2
   }
 
   dir_path
-  bootstrap_fwd (const dir_path& src_root, optional<bool>& altn)
+  bootstrap_fwd (context& ctx, const dir_path& src_root, optional<bool>& altn)
   {
     path f (exists (src_root, std_out_root_file, alt_out_root_file, altn));
 
@@ -420,7 +420,7 @@ namespace build2
     // We cannot just source the buildfile since there is no scope to do
     // this on yet.
     //
-    auto p (extract_variable (f, *var_out_root));
+    auto p (extract_variable (ctx, f, *var_out_root));
 
     if (!p.second)
       fail << "variable out_root expected as first line in " << f;
@@ -495,7 +495,7 @@ namespace build2
   }
 
   pair<value, bool>
-  extract_variable (const path& bf, const variable& var)
+  extract_variable (context& ctx, const path& bf, const variable& var)
   {
     try
     {
@@ -513,8 +513,8 @@ namespace build2
         return make_pair (value (), false);
       }
 
-      parser p;
-      temp_scope tmp (global_scope->rw ());
+      parser p (ctx);
+      temp_scope tmp (ctx.global_scope.rw ());
       p.parse_variable (lex, tmp, var, tt);
 
       value* v (tmp.vars.find_to_modify (var).first);
@@ -533,7 +533,8 @@ namespace build2
   // Extract the project name from bootstrap.build.
   //
   static project_name
-  find_project_name (const dir_path& out_root,
+  find_project_name (context& ctx,
+                     const dir_path& out_root,
                      const dir_path& fallback_src_root,
                      optional<bool> out_src, // True if out_root is src_root.
                      optional<bool>& altn)
@@ -544,7 +545,7 @@ namespace build2
     // in which case we will have src_root and maybe even the name.
     //
     const dir_path* src_root (nullptr);
-    const scope& s (scopes.find (out_root));
+    const scope& s (ctx.scopes.find (out_root));
 
     if (s.root_scope () == &s && s.out_path () == out_root)
     {
@@ -588,7 +589,7 @@ namespace build2
         }
         else
         {
-          auto p (extract_variable (f, *var_src_root));
+          auto p (extract_variable (ctx, f, *var_src_root));
 
           if (!p.second)
             fail << "variable src_root expected as first line in " << f;
@@ -610,7 +611,7 @@ namespace build2
       if (f.empty ())
         fail << "no build/bootstrap.build in " << *src_root;
 
-      auto p (extract_variable (f, *var_project));
+      auto p (extract_variable (ctx, f, *var_project));
 
       if (!p.second)
         fail << "variable " << var_project->name << " expected "
@@ -628,7 +629,8 @@ namespace build2
   // is a subproject, then enter it into the map, handling the duplicates.
   //
   static void
-  find_subprojects (subprojects& sps,
+  find_subprojects (context& ctx,
+                    subprojects& sps,
                     const dir_path& d,
                     const dir_path& root,
                     bool out)
@@ -668,7 +670,8 @@ namespace build2
         // Load its name. Note that here we don't use fallback src_root
         // since this function is used to scan both out_root and src_root.
         //
-        project_name name (find_project_name (sd, dir_path (), src, altn));
+        project_name name (
+          find_project_name (ctx, sd, dir_path (), src, altn));
 
         // If the name is empty, then is is an unnamed project. While the
         // 'project' variable stays empty, here we come up with a surrogate
@@ -707,26 +710,26 @@ namespace build2
   }
 
   bool
-  bootstrap_src (scope& root, optional<bool>& altn)
+  bootstrap_src (scope& rs, optional<bool>& altn)
   {
     tracer trace ("bootstrap_src");
 
     bool r (false);
 
-    const dir_path& out_root (root.out_path ());
-    const dir_path& src_root (root.src_path ());
+    const dir_path& out_root (rs.out_path ());
+    const dir_path& src_root (rs.src_path ());
 
     {
       path f (exists (src_root, std_bootstrap_file, alt_bootstrap_file, altn));
 
-      if (root.root_extra == nullptr)
+      if (rs.root_extra == nullptr)
       {
         // If nothing so far has indicated the naming, assume standard.
         //
         if (!altn)
           altn = false;
 
-        setup_root_extra (root, altn);
+        setup_root_extra (rs, altn);
       }
 
       if (!f.empty ())
@@ -736,8 +739,8 @@ namespace build2
         // process hard to reason about. But we may try to bootstrap the same
         // root scope multiple time.
         //
-        if (root.buildfiles.insert (f).second)
-          source (root, root, f, true);
+        if (rs.buildfiles.insert (f).second)
+          source (rs, rs, f, true);
         else
           l5 ([&]{trace << "skipping already sourced " << f;});
 
@@ -757,15 +760,15 @@ namespace build2
     // Note: the amalgamation variable value is always a relative directory.
     //
     {
-      auto rp (root.vars.insert (*var_amalgamation)); // Set NULL by default.
+      auto rp (rs.vars.insert (*var_amalgamation)); // Set NULL by default.
       value& v (rp.first);
 
       if (v && v.empty ()) // Convert empty to NULL.
         v = nullptr;
 
-      if (scope* aroot = root.parent_scope ()->root_scope ())
+      if (scope* ars = rs.parent_scope ()->root_scope ())
       {
-        const dir_path& ad (aroot->out_path ());
+        const dir_path& ad (ars->out_path ());
         dir_path rd (ad.relative (out_root));
 
         // If we already have the amalgamation variable set, verify
@@ -829,7 +832,7 @@ namespace build2
     // NULL value indicates that we found no subprojects.
     //
     {
-      auto rp (root.vars.insert (*var_subprojects)); // Set NULL by default.
+      auto rp (rs.vars.insert (*var_subprojects)); // Set NULL by default.
       value& v (rp.first);
 
       if (rp.second)
@@ -846,13 +849,13 @@ namespace build2
         if (exists (out_root))
         {
           l5 ([&]{trace << "looking for subprojects in " << out_root;});
-          find_subprojects (sps, out_root, out_root, true);
+          find_subprojects (rs.ctx, sps, out_root, out_root, true);
         }
 
         if (out_root != src_root)
         {
           l5 ([&]{trace << "looking for subprojects in " << src_root;});
-          find_subprojects (sps, src_root, src_root, false);
+          find_subprojects (rs.ctx, sps, src_root, src_root, false);
         }
 
         if (!sps.empty ()) // Keep it NULL if no subprojects.
@@ -923,7 +926,8 @@ namespace build2
               // Pass fallback src_root since this is a subproject that was
               // specified by the user so it is most likely in our src.
               //
-              n = find_project_name (out_root / d,
+              n = find_project_name (rs.ctx,
+                                     out_root / d,
                                      src_root / d,
                                      nullopt /* out_src */,
                                      altn);
@@ -1012,7 +1016,7 @@ namespace build2
     //
     return (out_root != src_root                        &&
             cast_false<bool> (orig.vars[var_forwarded]) &&
-            bootstrap_fwd (src_root, altn) == out_root);
+            bootstrap_fwd (orig.ctx, src_root, altn) == out_root);
   }
 
   void
@@ -1273,7 +1277,7 @@ namespace build2
     // over anything that we may discover. In particular, we will prefer it
     // over any bundled subprojects.
     //
-    auto& vp (var_pool.rw (iroot));
+    auto& vp (ibase.ctx.var_pool.rw (iroot));
 
     for (;;) // Break-out loop.
     {
@@ -1411,6 +1415,8 @@ namespace build2
       return names {move (target)};
     }
 
+    context& ctx (ibase.ctx);
+
     // Bootstrap the imported root scope. This is pretty similar to what we do
     // in main() except that here we don't try to guess src_root.
     //
@@ -1429,7 +1435,7 @@ namespace build2
     if (is_src_root (out_root, altn))
     {
       src_root = move (out_root);
-      out_root = bootstrap_fwd (src_root, altn);
+      out_root = bootstrap_fwd (ctx, src_root, altn);
       fwd = (src_root != out_root);
     }
 
@@ -1556,7 +1562,7 @@ namespace build2
       // there is a use-case for the export stub to return a qualified
       // name?
       //
-      parser p;
+      parser p (ctx);
       names v (p.parse_export_stub (ifs, es, iroot, ts));
 
       // If there were no export directive executed in an export stub, assume
@@ -1575,7 +1581,7 @@ namespace build2
   }
 
   const target*
-  import (const prerequisite_key& pk, bool existing)
+  import (context& ctx, const prerequisite_key& pk, bool existing)
   {
     tracer trace ("import");
 
@@ -1610,18 +1616,18 @@ namespace build2
 
         const exe* t (
           !existing
-          ? &targets.insert<exe> (tt,
-                                  p.directory (),
-                                  dir_path (),    // No out (out of project).
-                                  p.leaf ().base ().string (),
-                                  p.extension (), // Always specified.
-                                  trace)
-          : targets.find<exe> (tt,
-                               p.directory (),
-                               dir_path (),
-                               p.leaf ().base ().string (),
-                               p.extension (),
-                               trace));
+          ? &ctx.targets.insert<exe> (tt,
+                                      p.directory (),
+                                      dir_path (),    // No out (not in project).
+                                      p.leaf ().base ().string (),
+                                      p.extension (), // Always specified.
+                                      trace)
+          : ctx.targets.find<exe> (tt,
+                                   p.directory (),
+                                   dir_path (),
+                                   p.leaf ().base ().string (),
+                                   p.extension (),
+                                   trace));
 
         if (t != nullptr)
         {
diff --git a/libbuild2/file.hxx b/libbuild2/file.hxx
index 48d1b63..3909643 100644
--- a/libbuild2/file.hxx
+++ b/libbuild2/file.hxx
@@ -91,8 +91,8 @@ namespace build2
   source_once (scope& root, scope& base, const path&, scope& once);
 
   // Create project's root scope. Only set the src_root variable if the passed
-  // src_root value is not empty. The scope argument is only used as proof of
-  // lock.
+  // src_root value is not empty. The scope argument is only used for context
+  // and as a proof of lock.
   //
   LIBBUILD2_SYMEXPORT scope_map::iterator
   create_root (scope&, const dir_path& out_root, const dir_path& src_root);
@@ -140,7 +140,7 @@ namespace build2
   // argument semantics.
   //
   LIBBUILD2_SYMEXPORT dir_path
-  bootstrap_fwd (const dir_path& src_root, optional<bool>& altn);
+  bootstrap_fwd (context&, const dir_path& src_root, optional<bool>& altn);
 
   // Bootstrap the project's root scope, the out part.
   //
@@ -201,7 +201,7 @@ namespace build2
   // an indication of whether the variable was found.
   //
   LIBBUILD2_SYMEXPORT pair<value, bool>
-  extract_variable (const path&, const variable&);
+  extract_variable (context&, const path&, const variable&);
 
   // Import has two phases: the first is triggered by the import directive in
   // the buildfile. It will try to find and load the project. Failed that, it
@@ -224,7 +224,7 @@ namespace build2
   import (scope& base, name, const location&);
 
   const target&
-  import (const prerequisite_key&);
+  import (context&, const prerequisite_key&);
 
   // As above but only imports as an already existing target. Unlike the above
   // version, this one can be called during the execute phase.
@@ -232,7 +232,7 @@ namespace build2
   // Note: similar to search_existing().
   //
   const target*
-  import_existing (const prerequisite_key&);
+  import_existing (context&, const prerequisite_key&);
 }
 
 #include <libbuild2/file.ixx>
diff --git a/libbuild2/file.ixx b/libbuild2/file.ixx
index f8a79be..59b53bb 100644
--- a/libbuild2/file.ixx
+++ b/libbuild2/file.ixx
@@ -13,19 +13,19 @@ namespace build2
   }
 
   LIBBUILD2_SYMEXPORT const target*
-  import (const prerequisite_key&, bool existing);
+  import (context&, const prerequisite_key&, bool existing);
 
   inline const target&
-  import (const prerequisite_key& pk)
+  import (context& ctx, const prerequisite_key& pk)
   {
     assert (phase == run_phase::match);
-    return *import (pk, false);
+    return *import (ctx, pk, false);
   }
 
   inline const target*
-  import_existing (const prerequisite_key& pk)
+  import_existing (context& ctx, const prerequisite_key& pk)
   {
     assert (phase == run_phase::match || phase == run_phase::execute);
-    return import (pk, true);
+    return import (ctx, pk, true);
   }
 }
diff --git a/libbuild2/function.test.cxx b/libbuild2/function.test.cxx
index 2380987..670114e 100644
--- a/libbuild2/function.test.cxx
+++ b/libbuild2/function.test.cxx
@@ -41,7 +41,8 @@ namespace build2
     //
     init_diag (1);
     init (nullptr, argv[0]);
-    reset (strings ()); // No command line variables.
+    sched.startup (1);  // Serial execution.
+    context ctx (sched);
 
     function_family f ("dummy");
 
@@ -114,9 +115,9 @@ namespace build2
 
     try
     {
-      scope& s (*scope::global_);
+      scope& s (ctx.global_scope.rw ());
 
-      parser p;
+      parser p (ctx);
       p.parse_buildfile (cin, path ("buildfile"), s, s);
     }
     catch (const failed&)
diff --git a/libbuild2/in/init.cxx b/libbuild2/in/init.cxx
index a067ec3..8b27336 100644
--- a/libbuild2/in/init.cxx
+++ b/libbuild2/in/init.cxx
@@ -36,7 +36,7 @@ namespace build2
       // Enter variables.
       //
       {
-        auto& vp (var_pool.rw (rs));
+        auto& vp (rs.ctx.var_pool.rw (rs));
 
         // Alternative variable substitution symbol with '$' being the
         // default.
diff --git a/libbuild2/install/init.cxx b/libbuild2/install/init.cxx
index 060007b..dac337f 100644
--- a/libbuild2/install/init.cxx
+++ b/libbuild2/install/init.cxx
@@ -62,7 +62,7 @@ namespace build2
           vn += name;
         }
         vn += var;
-        const variable& vr (var_pool.rw (r).insert<CT> (move (vn), true));
+        const variable& vr (r.ctx.var_pool.rw (r).insert<CT> (move (vn), true));
 
         l = dv != nullptr
           ? config::required (r, vr, *dv, override).first
@@ -79,7 +79,7 @@ namespace build2
       vn = "install.";
       vn += name;
       vn += var;
-      const variable& vr (var_pool.rw (r).insert<T> (move (vn)));
+      const variable& vr (r.ctx.var_pool.rw (r).insert<T> (move (vn)));
 
       value& v (r.assign (vr));
 
@@ -122,7 +122,8 @@ namespace build2
       // This one doesn't have config.* value (only set in a buildfile).
       //
       if (!global)
-        var_pool.rw (r).insert<bool> (string ("install.") + n + ".subdirs");
+        r.ctx.var_pool.rw (r).insert<bool> (
+          string ("install.") + n + ".subdirs");
     }
 
     void
@@ -192,7 +193,7 @@ namespace build2
 
       // Enter module variables.
       //
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       // Note that the set_dir() calls below enter some more.
       //
diff --git a/libbuild2/install/rule.cxx b/libbuild2/install/rule.cxx
index 48a404b..478aadd 100644
--- a/libbuild2/install/rule.cxx
+++ b/libbuild2/install/rule.cxx
@@ -741,7 +741,7 @@ namespace build2
       cstrings args;
 
       string reld (
-        cast<string> ((*global_scope)["build.host.class"]) == "windows"
+        cast<string> (rs.ctx.global_scope["build.host.class"]) == "windows"
         ? msys_path (chd)
         : relative (chd).string ());
 
@@ -785,7 +785,7 @@ namespace build2
       dir_path chd (chroot_path (rs, base.dir));
 
       string reld (
-        cast<string> ((*global_scope)["build.host.class"]) == "windows"
+        cast<string> (rs.ctx.global_scope["build.host.class"]) == "windows"
         ? msys_path (chd)
         : relative (chd).string ());
 
diff --git a/libbuild2/install/utility.hxx b/libbuild2/install/utility.hxx
index 13fcceb..24c82d8 100644
--- a/libbuild2/install/utility.hxx
+++ b/libbuild2/install/utility.hxx
@@ -24,7 +24,7 @@ namespace build2
     {
       auto r (
         s.target_vars[tt]["*"].insert (
-          var_pool.rw (s).insert ("install")));
+          s.ctx.var_pool.rw (s).insert ("install")));
 
       if (r.second) // Already set by the user?
         r.first.get () = path_cast<path> (move (d));
@@ -42,7 +42,7 @@ namespace build2
     {
       auto r (
         s.target_vars[tt]["*"].insert (
-          var_pool.rw (s).insert ("install.mode")));
+          s.ctx.var_pool.rw (s).insert ("install.mode")));
 
       if (r.second) // Already set by the user?
         r.first.get () = move (m);
diff --git a/libbuild2/module.cxx b/libbuild2/module.cxx
index 1feb121..2ed3671 100644
--- a/libbuild2/module.cxx
+++ b/libbuild2/module.cxx
@@ -282,7 +282,7 @@ namespace build2
                     module_state {true, false, mf.init, nullptr, loc}).first;
     i->second.first = mf.boot (rs, loc, i->second.module);
 
-    rs.assign (var_pool.rw (rs).insert (mod + ".booted")) = true;
+    rs.assign (rs.ctx.var_pool.rw (rs).insert (mod + ".booted")) = true;
   }
 
   bool
@@ -333,7 +333,7 @@ namespace build2
     // buildfile-visible (where we use the term "load a module"; see the note
     // on terminology above)
     //
-    auto& vp (var_pool.rw (rs));
+    auto& vp (rs.ctx.var_pool.rw (rs));
     value& lv (bs.assign (vp.insert (mod + ".loaded")));
     value& cv (bs.assign (vp.insert (mod + ".configured")));
 
diff --git a/libbuild2/module.hxx b/libbuild2/module.hxx
index 200e52f..f583361 100644
--- a/libbuild2/module.hxx
+++ b/libbuild2/module.hxx
@@ -128,7 +128,7 @@ namespace build2
                const string& name,
                const location&,
                bool optional = false,
-               const variable_map& config_hints = variable_map ());
+               const variable_map& config_hints = empty_variable_map);
 
   // An alias to use from other modules (we could also distinguish between
   // boot and init).
@@ -142,7 +142,7 @@ namespace build2
                const string& name,
                const location& loc,
                bool optional = false,
-               const variable_map& config_hints = variable_map ())
+               const variable_map& config_hints = empty_variable_map)
   {
     return init_module (root, base, name, loc, optional, config_hints);
   }
diff --git a/libbuild2/operation.cxx b/libbuild2/operation.cxx
index 168ed5c..879d416 100644
--- a/libbuild2/operation.cxx
+++ b/libbuild2/operation.cxx
@@ -81,7 +81,7 @@ namespace build2
     // Create the base scope. Note that its existence doesn't mean it was
     // already setup as a base scope; it can be the same as root.
     //
-    auto i (scopes.rw (root).insert (out_base));
+    auto i (root.ctx.scopes.rw (root).insert (out_base));
     scope& base (setup_base (i, out_base, src_base));
 
     // Load the buildfile unless it is implied.
@@ -103,7 +103,7 @@ namespace build2
 
     phase_lock pl (run_phase::match);
 
-    const target* t (targets.find (tk, trace));
+    const target* t (bs.ctx.targets.find (tk, trace));
 
     // Only do the implied buildfile if we haven't loaded one. Failed that we
     // may try go this route even though we've concluded the implied buildfile
@@ -471,7 +471,7 @@ namespace build2
     if (rs.out_path () != out_base || rs.src_path () != src_base)
       fail (l) << "meta-operation info target must be project root directory";
 
-    setup_base (scopes.rw (rs).insert (out_base), out_base, src_base);
+    setup_base (rs.ctx.scopes.rw (rs).insert (out_base), out_base, src_base);
   }
 
   void
diff --git a/libbuild2/operation.hxx b/libbuild2/operation.hxx
index 86f93c6..0d56219 100644
--- a/libbuild2/operation.hxx
+++ b/libbuild2/operation.hxx
@@ -12,7 +12,6 @@
 
 #include <libbuild2/action.hxx>
 #include <libbuild2/variable.hxx>
-#include <libbuild2/prerequisite.hxx>
 #include <libbuild2/target-state.hxx>
 
 #include <libbuild2/export.hxx>
@@ -21,8 +20,10 @@ namespace build2
 {
   class location;
   class scope;
-  class target_key;
   class target;
+  class target_key;
+  class context;
+  class include_type;
   struct prerequisite_member;
 
   struct opspec;
@@ -275,7 +276,7 @@ namespace build2
     // If lifted is true then the operation name in opspec is bogus (has
     // been lifted) and the default/empty name should be assumed instead.
     //
-    using process_func = const string& (const variable_overrides&,
+    using process_func = const string& (context&,
                                         values&,
                                         vector_view<opspec>&,
                                         bool lifted,
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index c55d434..a05c898 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -129,13 +129,13 @@ namespace build2
                    tracer& tr)
     {
       auto r (process_target (p, n, o, loc));
-      return targets.insert (*r.first,        // target type
-                             move (n.dir),
-                             move (o.dir),
-                             move (n.value),
-                             move (r.second), // extension
-                             implied,
-                             tr).first;
+      return p.ctx.targets.insert (*r.first,        // target type
+                                   move (n.dir),
+                                   move (o.dir),
+                                   move (n.value),
+                                   move (r.second), // extension
+                                   implied,
+                                   tr).first;
     }
 
     // Only find.
@@ -148,12 +148,12 @@ namespace build2
                  tracer& tr)
     {
       auto r (process_target (p, n, o, loc));
-      return targets.find (*r.first, // target type
-                           n.dir,
-                           o.dir,
-                           n.value,
-                           r.second, // extension
-                           tr);
+      return p.ctx.targets.find (*r.first, // target type
+                                 n.dir,
+                                 o.dir,
+                                 n.value,
+                                 r.second, // extension
+                                 tr);
     }
 
     static pair<const target_type*, optional<string>>
@@ -1750,7 +1750,7 @@ namespace build2
       // Is this the 'foo=...' case?
       //
       size_t p (t.value.find ('='));
-      auto& vp (var_pool.rw (*scope_));
+      auto& vp (ctx.var_pool.rw (*scope_));
 
       if (p != string::npos)
         var = &vp.insert (split (p), true /* overridable */);
@@ -2452,7 +2452,7 @@ namespace build2
       //@@ TODO: append namespace if any.
     }
 
-    return var_pool.rw (*scope_).insert (move (n), true /* overridable */);
+    return ctx.var_pool.rw (*scope_).insert (move (n), true /* overridable */);
   }
 
   void parser::
@@ -2649,7 +2649,7 @@ namespace build2
       if (var.type == nullptr)
       {
         const bool o (true); // Allow overrides.
-        var_pool.update (const_cast<variable&> (var), type, nullptr, &o);
+        ctx.var_pool.update (const_cast<variable&> (var), type, nullptr, &o);
       }
       else if (var.type != type)
         fail (l) << "changing variable " << var << " type from "
@@ -5053,7 +5053,7 @@ namespace build2
     //
     lexer l (is, *path_, 1 /* line */, "\'\"\\$(");
     lexer_ = &l;
-    scope_ = root_ = scope::global_;
+    scope_ = root_ = &ctx.global_scope.rw ();
     pbase_ = &work; // Use current working directory.
     target_ = nullptr;
     prerequisite_ = nullptr;
@@ -5342,7 +5342,7 @@ namespace build2
 
     // Lookup.
     //
-    const auto& var (var_pool.rw (*scope_).insert (move (name), true));
+    const auto& var (ctx.var_pool.rw (*scope_).insert (move (name), true));
 
     if (p != nullptr)
     {
@@ -5435,12 +5435,12 @@ namespace build2
 
     target* ct (
       const_cast<target*> (                // Ok (serial execution).
-        targets.find (dir::static_type,    // Explicit current dir target.
-                      scope_->out_path (),
-                      dir_path (),         // Out tree target.
-                      string (),
-                      nullopt,
-                      trace)));
+        ctx.targets.find (dir::static_type,    // Explicit current dir target.
+                          scope_->out_path (),
+                          dir_path (),         // Out tree target.
+                          string (),
+                          nullopt,
+                          trace)));
 
     if (ct == nullptr)
     {
@@ -5449,13 +5449,13 @@ namespace build2
       // While this target is not explicitly mentioned in the buildfile, we
       // say that we behave as if it were. Thus not implied.
       //
-      ct = &targets.insert (dir::static_type,
-                            scope_->out_path (),
-                            dir_path (),
-                            string (),
-                            nullopt,
-                            false,
-                            trace).first;
+      ct = &ctx.targets.insert (dir::static_type,
+                                scope_->out_path (),
+                                dir_path (),
+                                string (),
+                                nullopt,
+                                false,
+                                trace).first;
       // Fall through.
     }
     else if (ct->implied)
@@ -5487,7 +5487,7 @@ namespace build2
       out = out_src (d, *root_);
     }
 
-    targets.insert<buildfile> (
+    ctx.targets.insert<buildfile> (
       move (d),
       move (out),
       p.leaf ().base ().string (),
diff --git a/libbuild2/parser.hxx b/libbuild2/parser.hxx
index 79cbead..2f70a18 100644
--- a/libbuild2/parser.hxx
+++ b/libbuild2/parser.hxx
@@ -22,6 +22,7 @@ namespace build2
 {
   class scope;
   class target;
+  class context;
   class prerequisite;
 
   class LIBBUILD2_SYMEXPORT parser
@@ -31,7 +32,8 @@ namespace build2
     // should only be bootstrapped.
     //
     explicit
-    parser (bool boot = false): fail ("error", &path_), boot_ (boot) {}
+    parser (context& c, bool boot = false)
+      : fail ("error", &path_), ctx (c), boot_ (boot) {}
 
     // Issue diagnostics and throw failed in case of an error.
     //
@@ -645,6 +647,8 @@ namespace build2
     const fail_mark fail;
 
   protected:
+    context& ctx;
+
     bool pre_parse_ = false;
     bool boot_;
 
diff --git a/libbuild2/prerequisite.cxx b/libbuild2/prerequisite.cxx
index 7355323..b73aa4e 100644
--- a/libbuild2/prerequisite.cxx
+++ b/libbuild2/prerequisite.cxx
@@ -64,7 +64,7 @@ namespace build2
         ext (to_ext (t.ext ())),
         scope (t.base_scope ()),
         target (&t),
-        vars (false /* global */)
+        vars (t.ctx, false /* global */)
   {
   }
 
diff --git a/libbuild2/prerequisite.hxx b/libbuild2/prerequisite.hxx
index f79ce04..3183a29 100644
--- a/libbuild2/prerequisite.hxx
+++ b/libbuild2/prerequisite.hxx
@@ -8,6 +8,7 @@
 #include <libbuild2/types.hxx>
 #include <libbuild2/utility.hxx>
 
+#include <libbuild2/scope.hxx>
 #include <libbuild2/action.hxx>
 #include <libbuild2/variable.hxx>
 #include <libbuild2/target-key.hxx>
@@ -17,7 +18,6 @@
 
 namespace build2
 {
-  class scope;
   class target;
 
   // Light-weight (by being shallow-pointing) prerequisite key, similar
@@ -31,7 +31,7 @@ namespace build2
   class prerequisite_key
   {
   public:
-    typedef build2::scope scope_type;
+    using scope_type = build2::scope;
 
     const optional<project_name>& proj;
     target_key tk;                // The .dir and .out members can be relative.
@@ -117,7 +117,7 @@ namespace build2
           name (move (n)),
           ext (move (e)),
           scope (s),
-          vars (false /* global */) {}
+          vars (s.ctx, false /* global */) {}
 
     // Make a prerequisite from a target.
     //
diff --git a/libbuild2/scope.cxx b/libbuild2/scope.cxx
index 1ad7455..ab81333 100644
--- a/libbuild2/scope.cxx
+++ b/libbuild2/scope.cxx
@@ -354,7 +354,7 @@ namespace build2
     // global scope.
     //
     if (inner_proj == nullptr)
-      inner_proj = global_scope;
+      inner_proj = &ctx.global_scope;
 
     // Now find our "stem", that is, the value to which we will be appending
     // suffixes and prepending prefixes. This is either the original or the
@@ -430,7 +430,7 @@ namespace build2
     // Check the cache.
     //
     variable_override_cache& cache (
-      inner_proj == global_scope
+      inner_proj == &ctx.global_scope
       ? global_override_cache
       : inner_proj->root_extra->override_cache);
 
@@ -595,7 +595,7 @@ namespace build2
     //
     for (const scope* s (this);
          s != nullptr;
-         s = s->root () ? global_scope : s->parent_scope ())
+         s = s->root () ? &s->global_scope () : s->parent_scope ())
     {
       if (s->target_types.empty ())
         continue;
@@ -619,7 +619,9 @@ namespace build2
   {
     // Pretty much the same logic as in find_target_type() above.
     //
-    for (; s != nullptr; s = s->root () ? global_scope : s->parent_scope ())
+    for (;
+         s != nullptr;
+         s = s->root () ? &s->global_scope () : s->parent_scope ())
     {
       if (s->target_types.empty ())
         continue;
@@ -730,7 +732,7 @@ namespace build2
     // factor it back into the name (this way we won't assert when printing
     // diagnostics; see to_stream(target_key) for details).
     //
-    if (ext                             &&
+    if (ext                              &&
         tt->fixed_extension   == nullptr &&
         tt->default_extension == nullptr)
     {
@@ -743,7 +745,8 @@ namespace build2
   }
 
   static target*
-  derived_tt_factory (const target_type& t, dir_path d, dir_path o, string n)
+  derived_tt_factory (context& c,
+                      const target_type& t, dir_path d, dir_path o, string n)
   {
     // Pass our type to the base factory so that it can detect that it is
     // being called to construct a derived target. This can be used, for
@@ -756,7 +759,7 @@ namespace build2
     const target_type* bt (t.base);
     for (; bt->factory == &derived_tt_factory; bt = bt->base) ;
 
-    target* r (bt->factory (t, move (d), move (o), move (n)));
+    target* r (bt->factory (c, t, move (d), move (o), move (n)));
     r->derived_type = &t;
     return r;
   }
@@ -818,23 +821,18 @@ namespace build2
     return target_types.insert (name, move (dt));
   }
 
-  scope* scope::global_;
+  //@@ CTX ??? sounds like should be in context!
   scope::variable_override_cache scope::global_override_cache;
 
   // scope_map
   //
-  scope_map scope_map::instance;
-  const scope_map& scope_map::cinstance = scope_map::instance;
-  const scope_map& scopes = scope_map::cinstance;
-
-  const scope* global_scope;
 
   auto scope_map::
   insert (const dir_path& k, bool root) -> iterator
   {
     scope_map_base& m (*this);
 
-    auto er (m.emplace (k, scope (true))); // Global.
+    auto er (m.emplace (k, scope (ctx, true /* global */)));
     scope& s (er.first->second);
 
     // If this is a new scope, update the parent chain.
diff --git a/libbuild2/scope.hxx b/libbuild2/scope.hxx
index 0c4094b..c3816dd 100644
--- a/libbuild2/scope.hxx
+++ b/libbuild2/scope.hxx
@@ -29,6 +29,10 @@ namespace build2
   class LIBBUILD2_SYMEXPORT scope
   {
   public:
+    // Context this scope belongs to.
+    //
+    context& ctx;
+
     // Absolute and normalized.
     //
     const dir_path& out_path () const {return *out_path_;}
@@ -71,6 +75,11 @@ namespace build2
     scope*       weak_scope ();
     const scope* weak_scope () const;
 
+    // Global scope.
+    //
+    scope&       global_scope () {return const_cast<scope&> (ctx.global_scope);}
+    const scope& global_scope () const {return ctx.global_scope;}
+
     // Return true if the specified root scope is a sub-scope of this root
     // scope. Note that both scopes must be root.
     //
@@ -102,7 +111,7 @@ namespace build2
     lookup
     operator[] (const string& name) const
     {
-      const variable* var (var_pool.find (name));
+      const variable* var (ctx.var_pool.find (name));
       return var != nullptr ? operator[] (*var) : lookup ();
     }
 
@@ -159,7 +168,7 @@ namespace build2
     value&
     assign (string name)
     {
-      return assign (variable_pool::instance.insert (move (name)));
+      return assign (ctx.var_pool.rw (*this).insert (move (name)));
     }
 
     // Assign a typed non-overridable variable with normal visibility.
@@ -168,7 +177,7 @@ namespace build2
     value&
     assign (string name)
     {
-      return vars.assign (variable_pool::instance.insert<T> (move (name)));
+      return vars.assign (ctx.var_pool.rw (*this).insert<T> (move (name)));
     }
 
     // Return a value suitable for appending. If the variable does not
@@ -337,14 +346,6 @@ namespace build2
       return const_cast<scope&> (*this);
     }
 
-    // RW access to global scope (RO via global global_scope below).
-    //
-    scope&
-    global () {return *global_;}
-
-  public:
-    static scope* global_; // Normally not accessed directly.
-
   private:
     friend class parser;
     friend class scope_map;
@@ -356,8 +357,8 @@ namespace build2
     friend LIBBUILD2_SYMEXPORT scope& create_bootstrap_inner (scope&,
                                                               const dir_path&);
 
-    explicit
-    scope (bool global): vars (global), target_vars (global) {}
+    scope (context& c, bool global)
+      : ctx (c), vars (c, global), target_vars (c, global) {}
 
     scope* parent_;
     scope* root_;
@@ -405,7 +406,7 @@ namespace build2
   {
   public:
     temp_scope (scope& p)
-        : scope (false) // Not global.
+        : scope (p.ctx, false /* global */)
     {
       out_path_ = p.out_path_;
       src_path_ = p.src_path_;
@@ -469,24 +470,21 @@ namespace build2
     rw (scope&) const {return const_cast<scope_map&> (*this);}
 
   private:
-    LIBBUILD2_SYMEXPORT static scope_map instance;
+    friend class context;
+
+    explicit
+    scope_map (context& c): ctx (c) {}
 
     // Entities that can access bypassing the lock proof.
     //
     friend int main (int, char*[]);
-    friend LIBBUILD2_SYMEXPORT variable_overrides reset (const strings&);
 
     LIBBUILD2_SYMEXPORT scope&
     find (const dir_path&);
 
-  public:
-    // For var_pool initialization.
-    //
-    LIBBUILD2_SYMEXPORT static const scope_map& cinstance;
+  private:
+    context& ctx;
   };
-
-  LIBBUILD2_SYMEXPORT extern const scope_map& scopes;
-  LIBBUILD2_SYMEXPORT extern const scope* global_scope;
 }
 
 #include <libbuild2/scope.ixx>
diff --git a/libbuild2/search.cxx b/libbuild2/search.cxx
index 917d750..199bc10 100644
--- a/libbuild2/search.cxx
+++ b/libbuild2/search.cxx
@@ -16,7 +16,7 @@ using namespace butl;
 namespace build2
 {
   const target*
-  search_existing_target (const prerequisite_key& pk)
+  search_existing_target (context& ctx, const prerequisite_key& pk)
   {
     tracer trace ("search_existing_target");
 
@@ -69,7 +69,8 @@ namespace build2
         o.clear ();
     }
 
-    const target* t (targets.find (*tk.type, d, o, *tk.name, tk.ext, trace));
+    const target* t (
+      ctx.targets.find (*tk.type, d, o, *tk.name, tk.ext, trace));
 
     if (t != nullptr)
       l5 ([&]{trace << "existing target " << *t
@@ -79,7 +80,7 @@ namespace build2
   }
 
   const target*
-  search_existing_file (const prerequisite_key& cpk)
+  search_existing_file (context& ctx, const prerequisite_key& cpk)
   {
     tracer trace ("search_existing_file");
 
@@ -184,7 +185,7 @@ namespace build2
     // Find or insert. Note that we are using our updated extension.
     //
     auto r (
-      targets.insert (
+      ctx.targets.insert (
         *tk.type, move (d), move (out), *tk.name, ext, true, trace));
 
     // Has to be a file_target.
@@ -201,7 +202,7 @@ namespace build2
   }
 
   const target&
-  create_new_target (const prerequisite_key& pk)
+  create_new_target (context& ctx, const prerequisite_key& pk)
   {
     tracer trace ("create_new_target");
 
@@ -227,13 +228,13 @@ namespace build2
     //
     // @@ OUT: same story as in search_existing_target() re out.
     //
-    auto r (targets.insert (*tk.type,
-                            move (d),
-                            *tk.out,
-                            *tk.name,
-                            tk.ext,
-                            true /* implied */,
-                            trace));
+    auto r (ctx.targets.insert (*tk.type,
+                                move (d),
+                                *tk.out,
+                                *tk.name,
+                                tk.ext,
+                                true /* implied */,
+                                trace));
 
     const target& t (r.first);
     l5 ([&]{trace << (r.second ? "new" : "existing") << " target " << t
diff --git a/libbuild2/search.hxx b/libbuild2/search.hxx
index b281b12..63ea6b1 100644
--- a/libbuild2/search.hxx
+++ b/libbuild2/search.hxx
@@ -13,12 +13,14 @@
 namespace build2
 {
   class target;
+  class context;
   class prerequisite_key;
 
-  // Search for an existing target in this prerequisite's scope.
+  // Search for an existing target in this prerequisite's scope. Scope can be
+  // NULL if directories are absolute.
   //
   LIBBUILD2_SYMEXPORT const target*
-  search_existing_target (const prerequisite_key&);
+  search_existing_target (context&, const prerequisite_key&);
 
   // Search for an existing file. If the prerequisite directory is relative,
   // then look in the scope's src directory. Otherwise, if the absolute
@@ -30,12 +32,12 @@ namespace build2
   // contains the search paths. But there wasn't any need for this yet.
   //
   LIBBUILD2_SYMEXPORT const target*
-  search_existing_file (const prerequisite_key&);
+  search_existing_file (context&, const prerequisite_key&);
 
   // Create a new target in this prerequisite's scope.
   //
   LIBBUILD2_SYMEXPORT const target&
-  create_new_target (const prerequisite_key&);
+  create_new_target (context&, const prerequisite_key&);
 }
 
 #endif // LIBBUILD2_SEARCH_HXX
diff --git a/libbuild2/target-key.hxx b/libbuild2/target-key.hxx
index e23991d..4df2b1f 100644
--- a/libbuild2/target-key.hxx
+++ b/libbuild2/target-key.hxx
@@ -53,7 +53,7 @@ namespace build2
     else
     {
       // Note that for performance reasons here we use the specified extension
-      // without calling fixed_extension().
+      // without calling fixed_extension() to verify it matches.
       //
       const char* xe (x.ext
                       ? x.ext->c_str ()
diff --git a/libbuild2/target-type.hxx b/libbuild2/target-type.hxx
index 3537c90..8b308c3 100644
--- a/libbuild2/target-type.hxx
+++ b/libbuild2/target-type.hxx
@@ -16,6 +16,7 @@ namespace build2
 {
   class scope;
   class target;
+  class context;
   class target_key;
   class prerequisite_key;
 
@@ -62,10 +63,15 @@ namespace build2
     const char* name;
     const target_type* base;
 
-    target* (*factory) (const target_type&, dir_path, dir_path, string);
+    target* (*factory) (context&,
+                        const target_type&,
+                        dir_path,
+                        dir_path,
+                        string);
 
     const char*      (*fixed_extension)   (const target_key&,
                                            const scope* root);
+
     optional<string> (*default_extension) (const target_key&,
                                            const scope& base,
                                            const char*,
diff --git a/libbuild2/target.cxx b/libbuild2/target.cxx
index c823e85..9749e94 100644
--- a/libbuild2/target.cxx
+++ b/libbuild2/target.cxx
@@ -67,7 +67,7 @@ namespace build2
   const string& target::
   ext (string v)
   {
-    ulock l (targets.mutex_);
+    ulock l (ctx.targets.mutex_);
 
     // Once the extension is set, it is immutable. However, it is possible
     // that someone has already "branded" this target with a different
@@ -102,7 +102,7 @@ namespace build2
     // If this target is from the src tree, use its out directory to find
     // the scope.
     //
-    return scopes.find (out_dir ());
+    return ctx.scopes.find (out_dir ());
   }
 
   const scope& target::
@@ -292,8 +292,6 @@ namespace build2
 
   // target_set
   //
-  target_set targets;
-
   const target* target_set::
   find (const target_key& k, tracer& trace) const
   {
@@ -374,7 +372,7 @@ namespace build2
         ? string (tt.fixed_extension (tk, nullptr /* root scope */))
         : move (tk.ext));
 
-      t = tt.factory (tt, move (dir), move (out), move (name));
+      t = tt.factory (ctx, tt, move (dir), move (out), move (name));
 
       // Re-lock for exclusive access. In the meantime, someone could have
       // inserted this target so emplace() below could return false, in which
@@ -658,25 +656,25 @@ namespace build2
   //
 
   const target*
-  target_search (const target&, const prerequisite_key& pk)
+  target_search (const target& t, const prerequisite_key& pk)
   {
     // The default behavior is to look for an existing target in the
     // prerequisite's directory scope.
     //
-    return search_existing_target (pk);
+    return search_existing_target (t.ctx, pk);
   }
 
   const target*
-  file_search (const target&, const prerequisite_key& pk)
+  file_search (const target& t, const prerequisite_key& pk)
   {
     // First see if there is an existing target.
     //
-    if (const target* t = search_existing_target (pk))
-      return t;
+    if (const target* e = search_existing_target (t.ctx, pk))
+      return e;
 
     // Then look for an existing file in the src tree.
     //
-    return search_existing_file (pk);
+    return search_existing_file (t.ctx, pk);
   }
 
   void
@@ -753,17 +751,17 @@ namespace build2
   };
 
   static const target*
-  alias_search (const target&, const prerequisite_key& pk)
+  alias_search (const target& t, const prerequisite_key& pk)
   {
     // For an alias we don't want to silently create a target since it will do
     // nothing and it most likely not what the user intended.
     //
-    const target* t (search_existing_target (pk));
+    const target* e (search_existing_target (t.ctx, pk));
 
-    if (t == nullptr || t->implied)
+    if (e == nullptr || e->implied)
       fail << "no explicit target for " << pk;
 
-    return t;
+    return e;
   }
 
   const target_type alias::static_type
@@ -847,16 +845,16 @@ namespace build2
   }
 
   static const target*
-  dir_search (const target&, const prerequisite_key& pk)
+  dir_search (const target& t, const prerequisite_key& pk)
   {
     tracer trace ("dir_search");
 
     // The first step is like in search_alias(): looks for an existing target.
     //
-    const target* t (search_existing_target (pk));
+    const target* e (search_existing_target (t.ctx, pk));
 
-    if (t != nullptr && !t->implied)
-      return t;
+    if (e != nullptr && !e->implied)
+      return e;
 
     // If not found (or is implied), then try to load the corresponding
     // buildfile (which would normally define this target). Failed that, see
@@ -905,10 +903,10 @@ namespace build2
         // have loaded the buildfile. So re-test now that we are in exclusive
         // phase.
         //
-        if (t == nullptr)
-          t = search_existing_target (pk);
+        if (e == nullptr)
+          e = search_existing_target (t.ctx, pk);
 
-        if (t != nullptr && !t->implied)
+        if (e != nullptr && !e->implied)
           retest = true;
         else
         {
@@ -933,8 +931,8 @@ namespace build2
             }
             else if (exists (src_base))
             {
-              t = dir::search_implied (base, pk, trace);
-              retest = (t != nullptr);
+              e = dir::search_implied (base, pk, trace);
+              retest = (e != nullptr);
             }
           }
         }
@@ -945,11 +943,11 @@ namespace build2
       //
       if (retest)
       {
-        if (t == nullptr)
-          t = search_existing_target (pk);
+        if (e == nullptr)
+          e = search_existing_target (t.ctx, pk);
 
-        if (t != nullptr && !t->implied)
-          return t;
+        if (e != nullptr && !e->implied)
+          return e;
       }
     }
 
@@ -1100,7 +1098,10 @@ namespace build2
       // Note: we are guaranteed the scope is never NULL for prerequisites
       // (where out/dir could be relative and none of this will work).
       //
+      // @@ CTX TODO
+#if 0
       root = scopes.find (tk.out->empty () ? *tk.dir : *tk.out).root_scope ();
+#endif
 
       if (root == nullptr || root->root_extra == nullptr)
         fail << "unable to determine extension for buildfile target " << tk;
diff --git a/libbuild2/target.hxx b/libbuild2/target.hxx
index 4bd11fe..5be1aab 100644
--- a/libbuild2/target.hxx
+++ b/libbuild2/target.hxx
@@ -123,9 +123,11 @@ namespace build2
   //
   class LIBBUILD2_SYMEXPORT target
   {
-    optional<string>* ext_; // Reference to value in target_key.
-
   public:
+    // Context this scope belongs to.
+    //
+    context& ctx;
+
     // For targets that are in the src tree of a project we also keep the
     // corresponding out directory. As a result we may end up with multiple
     // targets for the same file if we are building multiple configurations of
@@ -140,9 +142,10 @@ namespace build2
     // when src == out). We also treat out of project targets as being in the
     // out tree.
     //
-    const dir_path   dir;  // Absolute and normalized.
-    const dir_path   out;  // Empty or absolute and normalized.
-    const string     name;
+    const dir_path    dir;  // Absolute and normalized.
+    const dir_path    out;  // Empty or absolute and normalized.
+    const string      name;
+    optional<string>* ext_; // Reference to value in target_key.
 
     const string* ext () const; // Return NULL if not specified.
     const string& ext (string);
@@ -392,7 +395,7 @@ namespace build2
     lookup
     operator[] (const string& name) const
     {
-      const variable* var (var_pool.find (name));
+      const variable* var (ctx.var_pool.find (name));
       return var != nullptr ? operator[] (*var) : lookup ();
     }
 
@@ -530,7 +533,7 @@ namespace build2
       lookup
       operator[] (const string& name) const
       {
-        const variable* var (var_pool.find (name));
+        const variable* var (target_->ctx.var_pool.find (name));
         return var != nullptr ? operator[] (*var) : lookup ();
       }
 
@@ -563,7 +566,8 @@ namespace build2
       assign (const variable* var) {return vars.assign (var);} // For cached.
 
     public:
-      opstate (): vars (false /* global */) {}
+      explicit
+      opstate (context& c): vars (c, false /* global */) {}
 
     private:
       friend class target_set;
@@ -756,9 +760,11 @@ namespace build2
     // Targets should be created via the targets set below.
     //
   public:
-    target (dir_path d, dir_path o, string n)
-        : dir (move (d)), out (move (o)), name (move (n)),
-          vars (false /* global */) {}
+    target (context& c, dir_path d, dir_path o, string n)
+        : ctx (c),
+          dir (move (d)), out (move (o)), name (move (n)),
+          vars (c, false /* global */),
+          state {opstate (c), opstate (c)} {}
 
     target (target&&) = delete;
     target& operator= (target&&) = delete;
@@ -1377,13 +1383,17 @@ namespace build2
 
   private:
     friend class target; // Access to mutex.
+    friend class context;
+
+    explicit
+    target_set (context& c): ctx (c) {}
+
+    context& ctx;
 
     mutable shared_mutex mutex_;
     map_type map_;
   };
 
-  LIBBUILD2_SYMEXPORT extern target_set targets;
-
   // Modification time-based target.
   //
   class LIBBUILD2_SYMEXPORT mtime_target: public target
@@ -1752,9 +1762,10 @@ namespace build2
   //
   template <typename T>
   target*
-  target_factory (const target_type&, dir_path d, dir_path o, string n)
+  target_factory (context& c,
+                  const target_type&, dir_path d, dir_path o, string n)
   {
-    return new T (move (d), move (o), move (n));
+    return new T (c, move (d), move (o), move (n));
   }
 
   // Return fixed target extension unless one was specified.
diff --git a/libbuild2/target.ixx b/libbuild2/target.ixx
index 1671c25..fea87f3 100644
--- a/libbuild2/target.ixx
+++ b/libbuild2/target.ixx
@@ -13,7 +13,7 @@ namespace build2
   inline const string* target::
   ext () const
   {
-    slock l (targets.mutex_);
+    slock l (ctx.targets.mutex_);
     return *ext_ ? &**ext_ : nullptr;
   }
 
diff --git a/libbuild2/target.txx b/libbuild2/target.txx
index b93a403..8b17383 100644
--- a/libbuild2/target.txx
+++ b/libbuild2/target.txx
@@ -95,7 +95,7 @@ namespace build2
   {
     // Include target type/pattern-specific variables.
     //
-    if (auto l = s.find (var_pool[var], tt, tn))
+    if (auto l = s.find (s.ctx.var_pool[var], tt, tn))
     {
       // Help the user here and strip leading '.' from the extension.
       //
@@ -172,13 +172,13 @@ namespace build2
     // We behave as if this target was explicitly mentioned in the (implied)
     // buildfile. Thus not implied.
     //
-    target& t (targets.insert (dir::static_type,
-                               bs.out_path (),
-                               dir_path (),
-                               string (),
-                               nullopt,
-                               false,
-                               trace).first);
+    target& t (bs.ctx.targets.insert (dir::static_type,
+                                      bs.out_path (),
+                                      dir_path (),
+                                      string (),
+                                      nullopt,
+                                      false,
+                                      trace).first);
     t.prerequisites (move (ps));
     return &t;
   }
diff --git a/libbuild2/test/init.cxx b/libbuild2/test/init.cxx
index a5afea0..3fb4df6 100644
--- a/libbuild2/test/init.cxx
+++ b/libbuild2/test/init.cxx
@@ -39,7 +39,7 @@ namespace build2
       // Enter module variables. Do it during boot in case they get assigned
       // in bootstrap.build.
       //
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       common_data d {
 
@@ -109,7 +109,7 @@ namespace build2
         value& v (rs.assign (d.test_target));
 
         if (!v || v.empty ())
-          v = cast<target_triplet> ((*global_scope)["build.host"]);
+          v = cast<target_triplet> (rs.ctx.global_scope["build.host"]);
       }
 
       mod.reset (new module (move (d)));
diff --git a/libbuild2/test/rule.cxx b/libbuild2/test/rule.cxx
index 1d11063..50eb105 100644
--- a/libbuild2/test/rule.cxx
+++ b/libbuild2/test/rule.cxx
@@ -364,7 +364,7 @@ namespace build2
         build2::test::script::script s (t, ts, wd);
 
         {
-          parser p;
+          parser p (t.ctx);
           p.pre_parse (s);
 
           default_runner r (c);
diff --git a/libbuild2/test/script/builtin.cxx b/libbuild2/test/script/builtin.cxx
index ae979da..a725e17 100644
--- a/libbuild2/test/script/builtin.cxx
+++ b/libbuild2/test/script/builtin.cxx
@@ -956,7 +956,7 @@ namespace build2
 
           auto mv = [ops, &wd, &sp, &error] (const path& from, const path& to)
           {
-            const dir_path& rwd (sp.root->wd_path);
+            const dir_path& rwd (sp.root.wd_path);
 
             if (!from.sub (rwd) && !ops.force ())
               error () << "'" << from << "' is out of working directory '"
@@ -1158,7 +1158,7 @@ namespace build2
             error () << "missing file";
 
           const dir_path& wd  (sp.wd_path);
-          const dir_path& rwd (sp.root->wd_path);
+          const dir_path& rwd (sp.root.wd_path);
 
           while (scan.more ())
           {
@@ -1259,7 +1259,7 @@ namespace build2
             error () << "missing directory";
 
           const dir_path& wd  (sp.wd_path);
-          const dir_path& rwd (sp.root->wd_path);
+          const dir_path& rwd (sp.root.wd_path);
 
           while (scan.more ())
           {
diff --git a/libbuild2/test/script/parser.cxx b/libbuild2/test/script/parser.cxx
index 260bc88..a4aeff2 100644
--- a/libbuild2/test/script/parser.cxx
+++ b/libbuild2/test/script/parser.cxx
@@ -2866,7 +2866,7 @@ namespace build2
       {
         try
         {
-          parser p;
+          parser p (scr.test_target.ctx);
           p.execute (s, scr, r);
         }
         catch (const failed&)
diff --git a/libbuild2/test/script/parser.hxx b/libbuild2/test/script/parser.hxx
index 1beee49..e4d1f3a 100644
--- a/libbuild2/test/script/parser.hxx
+++ b/libbuild2/test/script/parser.hxx
@@ -16,6 +16,8 @@
 
 namespace build2
 {
+  class context;
+
   namespace test
   {
     namespace script
@@ -28,6 +30,8 @@ namespace build2
         // Pre-parse. Issue diagnostics and throw failed in case of an error.
         //
       public:
+        parser (context& c): build2::parser (c) {}
+
         void
         pre_parse (script&);
 
diff --git a/libbuild2/test/script/parser.test.cxx b/libbuild2/test/script/parser.test.cxx
index ab1f295..e45674b 100644
--- a/libbuild2/test/script/parser.test.cxx
+++ b/libbuild2/test/script/parser.test.cxx
@@ -9,7 +9,7 @@
 #include <libbuild2/utility.hxx>
 
 #include <libbuild2/target.hxx>
-#include <libbuild2/context.hxx>   // reset()
+#include <libbuild2/context.hxx>
 #include <libbuild2/scheduler.hxx>
 
 #include <libbuild2/test/target.hxx>
@@ -156,7 +156,7 @@ namespace build2
         init_diag (1);
         init (nullptr, argv[0]);
         sched.startup (1);  // Serial execution.
-        reset (strings ()); // No command line variables.
+        context ctx (sched);
 
         bool scope (false);
         bool id (false);
@@ -195,32 +195,32 @@ namespace build2
           // really care.
           //
           file& tt (
-            targets.insert<file> (work,
-                                  dir_path (),
-                                  "driver",
-                                  string (),
-                                  trace));
+            ctx.targets.insert<file> (work,
+                                      dir_path (),
+                                      "driver",
+                                      string (),
+                                      trace));
 
           value& v (
             tt.assign (
-              var_pool.rw ().insert<target_triplet> (
+              ctx.var_pool.rw ().insert<target_triplet> (
                 "test.target", variable_visibility::project)));
 
-          v = cast<target_triplet> ((*global_scope)["build.host"]);
+          v = cast<target_triplet> (ctx.global_scope["build.host"]);
 
           testscript& st (
-            targets.insert<testscript> (work,
-                                        dir_path (),
-                                        name.leaf ().base ().string (),
-                                        name.leaf ().extension (),
-                                        trace));
+            ctx.targets.insert<testscript> (work,
+                                            dir_path (),
+                                            name.leaf ().base ().string (),
+                                            name.leaf ().extension (),
+                                            trace));
 
           tt.path (path ("driver"));
           st.path (name);
 
           // Parse and run.
           //
-          parser p;
+          parser p (ctx);
           script s (tt, st, dir_path (work) /= "test-driver");
           p.pre_parse (cin, s);
 
diff --git a/libbuild2/test/script/runner.cxx b/libbuild2/test/script/runner.cxx
index f0c089b..c27ad39 100644
--- a/libbuild2/test/script/runner.cxx
+++ b/libbuild2/test/script/runner.cxx
@@ -299,7 +299,7 @@ namespace build2
           else
           {
             eop = path (op + ".orig");
-            save (eop, transform (rd.str, false, rd.modifiers, *sp.root), ll);
+            save (eop, transform (rd.str, false, rd.modifiers, sp.root), ll);
             sp.clean_special (eop);
           }
 
@@ -312,7 +312,7 @@ namespace build2
 
           // Ignore Windows newline fluff if that's what we are running on.
           //
-          if (test_target (*sp.root).class_ == "windows")
+          if (test_target (sp.root).class_ == "windows")
             args.push_back ("--strip-trailing-cr");
 
           args.push_back (eop.string ().c_str ());
@@ -451,14 +451,14 @@ namespace build2
             if (l.regex)                  // Regex (possibly empty),
             {
               r += rl.intro;
-              r += transform (l.value, true, rd.modifiers, *sp.root);
+              r += transform (l.value, true, rd.modifiers, sp.root);
               r += rl.intro;
               r += l.flags;
             }
             else if (!l.special.empty ()) // Special literal.
               r += rl.intro;
             else                          // Textual literal.
-              r += transform (l.value, false, rd.modifiers, *sp.root);
+              r += transform (l.value, false, rd.modifiers, sp.root);
 
             r += l.special;
             return r;
@@ -534,7 +534,7 @@ namespace build2
               {
                 try
                 {
-                  string s (transform (l.value, true, rd.modifiers, *sp.root));
+                  string s (transform (l.value, true, rd.modifiers, sp.root));
 
                   c = line_char (
                     char_regex (s, gf | parse_flags (l.flags)), pool);
@@ -571,7 +571,7 @@ namespace build2
               // Append literal line char.
               //
               rls += line_char (
-                transform (l.value, false, rd.modifiers, *sp.root), pool);
+                transform (l.value, false, rd.modifiers, sp.root), pool);
             }
 
             for (char c: l.special)
@@ -693,7 +693,7 @@ namespace build2
       bool default_runner::
       test (scope& s) const
       {
-        return common_.test (s.root->test_target, s.id_path);
+        return common_.test (s.root.test_target, s.id_path);
       }
 
       void default_runner::
@@ -724,7 +724,7 @@ namespace build2
           sp.parent == nullptr
           ? mkdir_buildignore (
             sp.wd_path,
-            sp.root->target_scope.root_scope ()->root_extra->buildignore_file,
+            sp.root.target_scope.root_scope ()->root_extra->buildignore_file,
             2)
           : mkdir (sp.wd_path, 2));
 
@@ -925,7 +925,7 @@ namespace build2
                 : (wd && sp.parent == nullptr
                    ? rmdir_buildignore (
                        d,
-                       sp.root->target_scope.root_scope ()->root_extra->buildignore_file,
+                       sp.root.target_scope.root_scope ()->root_extra->buildignore_file,
                        v)
                    : rmdir (d, v)));
 
@@ -1097,8 +1097,8 @@ namespace build2
           // locking as the variable pool is an associative container
           // (underneath) and we are only adding new variables into it.
           //
-          ulock ul (sp.root->var_pool_mutex);
-          const variable& var (sp.root->var_pool.insert (move (vname)));
+          ulock ul (sp.root.var_pool_mutex);
+          const variable& var (sp.root.var_pool.insert (move (vname)));
           ul.unlock ();
 
           value& lhs (sp.assign (var));
@@ -1123,7 +1123,7 @@ namespace build2
                 dr << info (ll) << "while parsing attributes '" << *ats << "'";
               });
 
-            parser p;
+            parser p (sp.root.test_target.ctx);
             p.apply_value_attributes (&var,
                                       lhs,
                                       value (move (ns)),
@@ -1175,7 +1175,7 @@ namespace build2
           const string& ls (np.leaf ().string ());
           bool wc (ls == "*" || ls == "**" || ls == "***");
           const path& cp (wc ? np.directory () : np);
-          const dir_path& wd (sp.root->wd_path);
+          const dir_path& wd (sp.root.wd_path);
 
           if (!cp.sub (wd))
             fail (ll) << (wc
@@ -1360,7 +1360,7 @@ namespace build2
               isp = std_path ("stdin");
 
               save (
-                isp, transform (in.str, false, in.modifiers, *sp.root), ll);
+                isp, transform (in.str, false, in.modifiers, sp.root), ll);
 
               sp.clean_special (isp);
 
diff --git a/libbuild2/test/script/script.cxx b/libbuild2/test/script/script.cxx
index b879eb4..af9ba82 100644
--- a/libbuild2/test/script/script.cxx
+++ b/libbuild2/test/script/script.cxx
@@ -418,12 +418,12 @@ namespace build2
       // scope
       //
       scope::
-      scope (const string& id, scope* p, script* r)
+      scope (const string& id, scope* p, script& r)
           : parent (p),
             root (r),
-            vars (false /* global */),
-            id_path (cast<path> (assign (root->id_var) = path ())),
-            wd_path (cast<dir_path> (assign (root->wd_var) = dir_path ()))
+            vars (r.test_target.ctx, false /* global */),
+            id_path (cast<path> (assign (root.id_var) = path ())),
+            wd_path (cast<dir_path> (assign (root.wd_var) = dir_path ()))
 
       {
         // Construct the id_path as a string to ensure POSIX form. In fact,
@@ -455,7 +455,7 @@ namespace build2
         assert (!implicit || c.type == cleanup_type::always);
 
         const path& p (c.path);
-        if (!p.sub (root->wd_path))
+        if (!p.sub (root.wd_path))
         {
           if (implicit)
             return;
@@ -481,8 +481,11 @@ namespace build2
       // script_base
       //
       script_base::
-      script_base ()
-          : // Enter the test.* variables with the same variable types as in
+      script_base (const target& tt, const testscript& st)
+          : test_target (tt),
+            target_scope (tt.base_scope ()),
+            script_target (st),
+            // Enter the test.* variables with the same variable types as in
             // buildfiles except for test: while in buildfiles it can be a
             // target name, in testscripts it should be resolved to a path.
             //
@@ -515,10 +518,8 @@ namespace build2
       script (const target& tt,
               const testscript& st,
               const dir_path& rwd)
-          : group (st.name == "testscript" ? string () : st.name, this),
-            test_target (tt),
-            target_scope (tt.base_scope ()),
-            script_target (st)
+          : script_base (tt, st),
+            group (st.name == "testscript" ? string () : st.name, *this)
       {
         // Set the script working dir ($~) to $out_base/test/<id> (id_path
         // for root is just the id which is empty if st is 'testscript').
@@ -634,12 +635,11 @@ namespace build2
         // in parallel). Plus, if there is no such variable, then we cannot
         // possibly find any value.
         //
-        const variable* pvar (build2::var_pool.find (n));
+        const variable* pvar (root.test_target.ctx.var_pool.find (n));
 
         if (pvar == nullptr)
           return lookup ();
 
-        const script& s (static_cast<const script&> (*root));
         const variable& var (*pvar);
 
         // First check the target we are testing.
@@ -649,12 +649,12 @@ namespace build2
           // value. In this case, presumably the override also affects the
           // script target and we will pick it up there. A bit fuzzy.
           //
-          auto p (s.test_target.find_original (var, target_only));
+          auto p (root.test_target.find_original (var, target_only));
 
           if (p.first)
           {
             if (var.overrides != nullptr)
-              p = s.target_scope.find_override (var, move (p), true);
+              p = root.target_scope.find_override (var, move (p), true);
 
             return p.first;
           }
@@ -665,7 +665,7 @@ namespace build2
         // in different scopes which brings the question of which scopes we
         // should search.
         //
-        return s.script_target[var];
+        return root.script_target[var];
       }
 
       value& scope::
@@ -696,30 +696,30 @@ namespace build2
           s.insert (s.end (), v.begin (), v.end ());
         };
 
-        if (lookup l = find (root->test_var))
+        if (lookup l = find (root.test_var))
           s.push_back (cast<path> (l).representation ());
 
-        if (lookup l = find (root->options_var))
+        if (lookup l = find (root.options_var))
           append (cast<strings> (l));
 
-        if (lookup l = find (root->arguments_var))
+        if (lookup l = find (root.arguments_var))
           append (cast<strings> (l));
 
         // Keep redirects/cleanups out of $N.
         //
         size_t n (s.size ());
 
-        if (lookup l = find (root->redirects_var))
+        if (lookup l = find (root.redirects_var))
           append (cast<strings> (l));
 
-        if (lookup l = find (root->cleanups_var))
+        if (lookup l = find (root.cleanups_var))
           append (cast<strings> (l));
 
         // Set the $N values if present.
         //
         for (size_t i (0); i <= 9; ++i)
         {
-          value& v (assign (*root->cmdN_var[i]));
+          value& v (assign (*root.cmdN_var[i]));
 
           if (i < n)
           {
@@ -734,7 +734,7 @@ namespace build2
 
         // Set $*.
         //
-        assign (root->cmd_var) = move (s);
+        assign (root.cmd_var) = move (s);
       }
     }
   }
diff --git a/libbuild2/test/script/script.hxx b/libbuild2/test/script/script.hxx
index e3f8251..8b34be8 100644
--- a/libbuild2/test/script/script.hxx
+++ b/libbuild2/test/script/script.hxx
@@ -343,7 +343,7 @@ namespace build2
       {
       public:
         scope* const parent; // NULL for the root (script) scope.
-        script* const root;  // Self for the root (script) scope.
+        script&      root;   // Self for the root (script) scope.
 
         // The chain of if-else scope alternatives. See also if_cond_ below.
         //
@@ -424,7 +424,7 @@ namespace build2
         ~scope () = default;
 
       protected:
-        scope (const string& id, scope* parent, script* root);
+        scope (const string& id, scope* parent, script& root);
 
         // Pre-parse data.
         //
@@ -452,7 +452,7 @@ namespace build2
         group (const string& id, group& p): scope (id, &p, p.root) {}
 
       protected:
-        group (const string& id, script* r): scope (id, nullptr, r) {}
+        group (const string& id, script& r): scope (id, nullptr, r) {}
 
         // Pre-parse data.
         //
@@ -505,7 +505,13 @@ namespace build2
       class script_base // Make sure certain things are initialized early.
       {
       protected:
-        script_base ();
+        script_base (const target& test_target,
+                     const testscript& script_target);
+
+      public:
+        const target&        test_target;   // Target we are testing.
+        const build2::scope& target_scope;  // Base scope of test target.
+        const testscript&    script_target; // Target of the testscript file.
 
       public:
         variable_pool var_pool;
@@ -535,11 +541,6 @@ namespace build2
         script& operator= (script&&) = delete;
         script& operator= (const script&) = delete;
 
-      public:
-        const target&        test_target;   // Target we are testing.
-        const build2::scope& target_scope;  // Base scope of test target.
-        const testscript&    script_target; // Target of the testscript file.
-
         // Pre-parse data.
         //
       private:
diff --git a/libbuild2/variable.cxx b/libbuild2/variable.cxx
index c921bbd..84c1fb3 100644
--- a/libbuild2/variable.cxx
+++ b/libbuild2/variable.cxx
@@ -1380,12 +1380,10 @@ namespace build2
     }
   }
 
-  variable_pool variable_pool::instance (true);
-  const variable_pool& variable_pool::cinstance = variable_pool::instance;
-  const variable_pool& var_pool = variable_pool::cinstance;
-
   // variable_map
   //
+  const variable_map empty_variable_map (nullptr /* context */);
+
   auto variable_map::
   find (const variable& var, bool typed) const ->
     pair<const value_data*, const variable&>
diff --git a/libbuild2/variable.hxx b/libbuild2/variable.hxx
index 9a106b5..d153cb0 100644
--- a/libbuild2/variable.hxx
+++ b/libbuild2/variable.hxx
@@ -16,6 +16,7 @@
 #include <libbuild2/types.hxx>
 #include <libbuild2/utility.hxx>
 
+#include <libbuild2/context.hxx>
 #include <libbuild2/target-type.hxx>
 
 #include <libbuild2/export.hxx>
@@ -1018,7 +1019,7 @@ namespace build2
 
   // Variable pool.
   //
-  // The global version is protected by the phase mutex.
+  // The global (as in, context-wide) version is protected by the phase mutex.
   //
   class variable_pool
   {
@@ -1175,9 +1176,12 @@ namespace build2
     variable_pool&
     rw (scope&) const {return const_cast<variable_pool&> (*this);}
 
-  private:
-    LIBBUILD2_SYMEXPORT static variable_pool instance;
+    // Entities that can access bypassing the lock proof.
+    //
+    friend class parser;
+    friend class scope;
 
+  private:
     LIBBUILD2_SYMEXPORT variable&
     insert (string name,
             const value_type*,
@@ -1191,17 +1195,6 @@ namespace build2
             const variable_visibility* = nullptr,
             const bool* = nullptr) const;
 
-    // Entities that can access bypassing the lock proof.
-    //
-    friend class parser;
-    friend class scope;
-    friend LIBBUILD2_SYMEXPORT variable_overrides reset (const strings&);
-
-  public:
-    // For var_pool initialization.
-    //
-    LIBBUILD2_SYMEXPORT static const variable_pool& cinstance;
-
     // Variable map.
     //
   private:
@@ -1261,13 +1254,13 @@ namespace build2
     // Global pool flag.
     //
   private:
+    friend class context;
+
     explicit
     variable_pool (bool global): global_ (global) {}
 
     bool global_;
   };
-
-  LIBBUILD2_SYMEXPORT extern const variable_pool& var_pool;
 }
 
 // variable_map
@@ -1361,7 +1354,9 @@ namespace build2
     lookup
     operator[] (const string& name) const
     {
-      const variable* var (var_pool.find (name));
+      const variable* var (ctx != nullptr
+                           ? ctx->var_pool.find (name)
+                           : nullptr);
       return var != nullptr ? operator[] (*var) : lookup ();
     }
 
@@ -1402,7 +1397,7 @@ namespace build2
     // Note that the variable is expected to have already been registered.
     //
     value&
-    assign (const string& name) {return insert (var_pool[name]).first;}
+    assign (const string& name) {return insert (ctx->var_pool[name]).first;}
 
     // As above but also return an indication of whether the new value (which
     // will be NULL) was actually inserted. Similar to find(), if typed is
@@ -1436,11 +1431,18 @@ namespace build2
     // (e.g., scopes, etc).
     //
     explicit
-    variable_map (bool global = false): global_ (global) {}
+    variable_map (context& c, bool global = false)
+      : ctx (&c), global_ (global) {}
 
     void
     clear () {m_.clear ();}
 
+    // Implementation details.
+    //
+  public:
+    explicit
+    variable_map (context* c): ctx (c) {}
+
   private:
     friend class variable_type_map;
 
@@ -1448,10 +1450,13 @@ namespace build2
     typify (const value_data&, const variable&) const;
 
   private:
-    bool global_;
+    context* ctx;
     map_type m_;
+    bool global_;
   };
 
+  extern const variable_map empty_variable_map;
+
   // Value caching. Used for overrides as well as target type/pattern-specific
   // append/prepend.
   //
@@ -1528,13 +1533,13 @@ namespace build2
     using const_iterator = map_type::const_iterator;
     using const_reverse_iterator = map_type::const_reverse_iterator;
 
-    explicit
-    variable_pattern_map (bool global): global_ (global) {}
+    variable_pattern_map (context& c, bool global)
+        : ctx (c), global_ (global) {}
 
     variable_map&
     operator[] (const string& v)
     {
-      return map_.emplace (v, variable_map (global_)).first->second;
+      return map_.emplace (v, variable_map (ctx, global_)).first->second;
     }
 
     const_iterator         begin ()  const {return map_.begin ();}
@@ -1544,8 +1549,10 @@ namespace build2
     bool                   empty ()  const {return map_.empty ();}
 
   private:
-    bool global_;
+    context& ctx;
     map_type map_;
+    bool global_;
+
   };
 
   class LIBBUILD2_SYMEXPORT variable_type_map
@@ -1555,13 +1562,13 @@ namespace build2
                               variable_pattern_map>;
     using const_iterator = map_type::const_iterator;
 
-    explicit
-    variable_type_map (bool global): global_ (global) {}
+    variable_type_map (context& c, bool global): ctx (c), global_ (global) {}
 
     variable_pattern_map&
     operator[] (const target_type& t)
     {
-      return map_.emplace (t, variable_pattern_map (global_)).first->second;
+      return map_.emplace (
+        t, variable_pattern_map (ctx, global_)).first->second;
     }
 
     const_iterator begin () const {return map_.begin ();}
@@ -1585,8 +1592,10 @@ namespace build2
     cache;
 
   private:
-    bool global_;
+    context& ctx;
     map_type map_;
+    bool global_;
+
   };
 }
 
diff --git a/libbuild2/version/init.cxx b/libbuild2/version/init.cxx
index a4e41d6..faa6e38 100644
--- a/libbuild2/version/init.cxx
+++ b/libbuild2/version/init.cxx
@@ -219,7 +219,7 @@ namespace build2
 
       // Set all the version.* variables.
       //
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       auto set = [&vp, &rs] (const char* var, auto val)
       {
diff --git a/tests/libbuild2/driver.cxx b/tests/libbuild2/driver.cxx
index 706d276..8ae83d5 100644
--- a/tests/libbuild2/driver.cxx
+++ b/tests/libbuild2/driver.cxx
@@ -5,7 +5,7 @@
 #include <libbuild2/types.hxx>
 #include <libbuild2/utility.hxx>
 
-#include <libbuild2/context.hxx>   // sched, reset()
+#include <libbuild2/context.hxx>
 #include <libbuild2/scheduler.hxx>
 
 #include <libbuild2/in/init.hxx>
@@ -26,8 +26,8 @@ main (int, char* argv[])
   in::build2_in_load ();
   version::build2_version_load ();
 
-  sched.startup (1);  // Serial execution.
-  reset (strings ()); // No command line variables.
+  sched.startup (1);   // Serial execution.
+  context ctx (sched);
 
   return 0;
 }