From 58e495733d402bb4e97238ae6c8e8344eb4b2161 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 19 Sep 2022 14:17:10 +0200
Subject: Add target_lock::first to distinguish first lock of target

---
 libbuild2/algorithm.cxx | 16 +++++++++-------
 libbuild2/algorithm.hxx |  4 +++-
 libbuild2/algorithm.ixx |  6 +++---
 3 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/libbuild2/algorithm.cxx b/libbuild2/algorithm.cxx
index 76f7c4c..696a09d 100644
--- a/libbuild2/algorithm.cxx
+++ b/libbuild2/algorithm.cxx
@@ -256,7 +256,7 @@ namespace build2
           fail << "dependency cycle detected involving target " << ct;
 
         if (!wq)
-          return target_lock {a, nullptr, e - b};
+          return target_lock {a, nullptr, e - b, false};
 
         // We also unlock the phase for the duration of the wait. Why?
         // Consider this scenario: we are trying to match a dir{} target whose
@@ -272,7 +272,7 @@ namespace build2
       // We don't lock already applied or executed targets.
       //
       if (e >= appl)
-        return target_lock {a, nullptr, e - b};
+        return target_lock {a, nullptr, e - b, false};
     }
 
     // We now have the lock. Analyze the old value and decide what to do.
@@ -281,7 +281,8 @@ namespace build2
     target::opstate& s (t[a]);
 
     size_t offset;
-    if (e <= b)
+    bool first;
+    if ((first = (e <= b)))
     {
       // First lock for this operation.
       //
@@ -298,7 +299,7 @@ namespace build2
               offset == target::offset_matched);
     }
 
-    return target_lock {a, &t, offset};
+    return target_lock {a, &t, offset, first};
   }
 
   void
@@ -991,7 +992,7 @@ namespace build2
             *task_count,
             [a, try_match] (const diag_frame* ds,
                             const target_lock* ls,
-                            target& t, size_t offset)
+                            target& t, size_t offset, bool first)
             {
               // Switch to caller's diag and lock stacks.
               //
@@ -1002,7 +1003,7 @@ namespace build2
               {
                 phase_lock pl (t.ctx, run_phase::match); // Throws.
                 {
-                  target_lock l {a, &t, offset}; // Reassemble.
+                  target_lock l {a, &t, offset, first}; // Reassemble.
                   match_impl (l, false /* step */, try_match);
                   // Unlock within the match phase.
                 }
@@ -1012,7 +1013,8 @@ namespace build2
             diag_frame::stack (),
             target_lock::stack (),
             ref (*ld.target),
-            ld.offset))
+            ld.offset,
+            ld.first))
         return make_pair (true, target_state::postponed); // Queued.
 
       // Matched synchronously, fall through.
diff --git a/libbuild2/algorithm.hxx b/libbuild2/algorithm.hxx
index b7f6809..e558d3a 100644
--- a/libbuild2/algorithm.hxx
+++ b/libbuild2/algorithm.hxx
@@ -191,6 +191,7 @@ namespace build2
     action_type  action;
     target_type* target = nullptr;
     size_t       offset = 0;
+    bool         first;
 
     explicit operator bool () const {return target != nullptr;}
 
@@ -209,13 +210,14 @@ namespace build2
     // Implementation details.
     //
     ~target_lock ();
-    target_lock (action_type, target_type*, size_t);
+    target_lock (action_type, target_type*, size_t, bool);
 
     struct data
     {
       action_type action;
       target_type* target;
       size_t offset;
+      bool first;
     };
 
     data
diff --git a/libbuild2/algorithm.ixx b/libbuild2/algorithm.ixx
index 8fc5390..417a10e 100644
--- a/libbuild2/algorithm.ixx
+++ b/libbuild2/algorithm.ixx
@@ -220,8 +220,8 @@ namespace build2
   unlock_impl (action, target&, size_t);
 
   inline target_lock::
-  target_lock (action_type a, target_type* t, size_t o)
-      : action (a), target (t), offset (o)
+  target_lock (action_type a, target_type* t, size_t o, bool f)
+      : action (a), target (t), offset (o), first (f)
   {
     if (target != nullptr)
       prev = stack (this);
@@ -260,7 +260,7 @@ namespace build2
   inline auto target_lock::
   release () -> data
   {
-    data r {action, target, offset};
+    data r {action, target, offset, first};
 
     if (target != nullptr)
     {
-- 
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