From d1d1d444f0b4abbb628625240025bfe3cfe77459 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 6 Mar 2017 09:57:15 +0200
Subject: Tweak target locking logic

---
 build2/algorithm.cxx | 27 ++++++++++++++-------------
 build2/target.cxx    | 11 ++++-------
 2 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/build2/algorithm.cxx b/build2/algorithm.cxx
index c4342d3..4e5ec78 100644
--- a/build2/algorithm.cxx
+++ b/build2/algorithm.cxx
@@ -104,7 +104,6 @@ namespace build2
     size_t b (target::count_base ());
     size_t e (b + target::offset_touched - 1);
 
-    size_t exec (b + target::offset_executed);
     size_t lock (b + target::offset_locked);
     size_t busy (b + target::offset_busy);
 
@@ -147,18 +146,6 @@ namespace build2
         for (; e == lock; e = ct.task_count.load (memory_order_acquire))
           this_thread::yield ();
       }
-
-      // We don't lock already executed targets.
-      //
-      if (e == exec)
-      {
-        // Sanity check: we better not be overriding a recipe for an already
-        // executed target.
-        //
-        assert (ct.action == a);
-
-        return target_lock {nullptr, target::offset_executed};
-      }
     }
 
     // We now have the sping lock. Analyze the old value and decide what to
@@ -181,6 +168,20 @@ namespace build2
 
       switch (offset)
       {
+      case target::offset_executed:
+        {
+          if (a == t.action)
+          {
+            // We don't lock already executed targets.
+            //
+            t.task_count.store (e, memory_order_release);
+            return target_lock {nullptr, target::offset_executed};
+          }
+
+          // Override, fall through.
+          //
+          assert (a > t.action);
+        }
       case target::offset_touched:
       case target::offset_matched:
       case target::offset_applied:
diff --git a/build2/target.cxx b/build2/target.cxx
index dacf534..fa8378c 100644
--- a/build2/target.cxx
+++ b/build2/target.cxx
@@ -149,15 +149,12 @@ namespace build2
       if (e >= busy)
         return target_state::unchanged; // Override in progress.
 
+      // Unlike lock_impl(), we are only called after being matched for this
+      // action so if we see executed, then it means executed for this action
+      // (or noop).
+      //
       if (e == exec)
-      {
-        // Sanity check: we better not be overriding a recipe for an already
-        // executed target.
-        //
-        assert (action == a);
-
         return group_state () ? group->state_ : state_;
-      }
 
       // Try to grab the spin-lock.
       //
-- 
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