From d27390e9935c94938af9e7068557d6f6ef9b07a9 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 12 Dec 2024 11:30:27 +0200
Subject: Increment load_generation between operations in batch

---
 build2/b.cxx          |  6 ++++++
 libbuild2/cc/init.cxx |  2 +-
 libbuild2/context.cxx |  7 +++++++
 libbuild2/context.hxx | 19 ++++++++++++++++---
 libbuild2/module.cxx  |  2 ++
 5 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/build2/b.cxx b/build2/b.cxx
index 0b4ec3a..f357722 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -831,6 +831,12 @@ main (int argc, char* argv[])
         if (!oname.empty () && lift ())
           break;
 
+        // Increment load generation for subsequent operations in a batch
+        // since they may load additional buildfiles.
+        //
+        if (mid != 0)
+          ctx.load_generation++;
+
         // Next bootstrap projects for all the target so that all the variable
         // overrides are set (if we also load/search/match in the same loop
         // then we may end up loading a project (via import) before this
diff --git a/libbuild2/cc/init.cxx b/libbuild2/cc/init.cxx
index d691bc5..64c70f8 100644
--- a/libbuild2/cc/init.cxx
+++ b/libbuild2/cc/init.cxx
@@ -764,7 +764,7 @@ namespace build2
               perform_update_id,
               context::operation_callback {&compiledb_pre, &compiledb_post});
 
-          if (ctx.load_generation > 1)
+          if (!ctx.phase_mutex.unlocked ()) // Interrupting load.
           {
             action a (ctx.current_action ());
 
diff --git a/libbuild2/context.cxx b/libbuild2/context.cxx
index 6e4fd6f..31d218b 100644
--- a/libbuild2/context.cxx
+++ b/libbuild2/context.cxx
@@ -1061,6 +1061,13 @@ namespace build2
     return r ? optional<bool> (s) : nullopt;
   }
 
+  bool run_phase_mutex::
+  unlocked () const
+  {
+    mlock l (m_);
+    return lc_ == 0 && mc_ == 0 && ec_ == 0;
+  }
+
   // C++17 deprecated uncaught_exception() so use uncaught_exceptions() if
   // available.
   //
diff --git a/libbuild2/context.hxx b/libbuild2/context.hxx
index 46dbfaa..12b11d5 100644
--- a/libbuild2/context.hxx
+++ b/libbuild2/context.hxx
@@ -49,6 +49,12 @@ namespace build2
     optional<bool>
     relock (run_phase unlock, run_phase lock);
 
+    // Return true if the mutex is unlocked, meaning we are in the initial
+    // load phase.
+    //
+    bool
+    unlocked () const;
+
     // Statistics.
     //
   public:
@@ -78,7 +84,7 @@ namespace build2
     //
     context& ctx_;
 
-    mutex m_;
+    mutable mutex m_;
 
     bool fail_;
 
@@ -209,8 +215,12 @@ namespace build2
     // hierarchy would "see" a new value from the newly inserted scope.
     //
     // The special load_generation value 0 indicates initialization before
-    // anything has been loaded. Currently, it is changed to 1 at the end
-    // of the context constructor.
+    // anything has been loaded. Currently, it is changed to 1 at the end of
+    // the context constructor. Note also that subsequent operations in a
+    // batch may trigger loading of additional buildfiles, in fact, entire new
+    // projects. As a result, load_generation is also incremented after each
+    // operation in a batch. If you need to detect the initial load in each
+    // operation, check that phase_mutex is unlocked.
     //
     // Note must come (and thus initialized) before the data_ member.
     //
@@ -817,6 +827,9 @@ namespace build2
 
     // Set current meta-operation and operation.
     //
+    // Remember to also increment load_generation for subsequent operations in
+    // a batch if additional buildfiles are loaded between them.
+    //
     // Note that the context instance is not to be re-used between different
     // meta-operations.
     //
diff --git a/libbuild2/module.cxx b/libbuild2/module.cxx
index df0da48..9a12d01 100644
--- a/libbuild2/module.cxx
+++ b/libbuild2/module.cxx
@@ -204,6 +204,8 @@ namespace build2
                         0,       /* diag (none) */
                         false    /* progress */);
 
+    ctx.module_context->load_generation++;
+
     assert (tgs.size () == 1);
     return tgs[0].as<target> ();
   }
-- 
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