From 3875999b2642013dfddd6cb1fa7b3ee7ac14f9d7 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 25 Jun 2020 08:05:00 +0200
Subject: Eliminate phase unlock for case where we are not going to wait

---
 libbuild2/context.ixx | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

(limited to 'libbuild2/context.ixx')

diff --git a/libbuild2/context.ixx b/libbuild2/context.ixx
index 46fe4f7..73601d4 100644
--- a/libbuild2/context.ixx
+++ b/libbuild2/context.ixx
@@ -56,8 +56,12 @@ namespace build2
   inline void wait_guard::
   wait ()
   {
-    phase_unlock u (*ctx, phase);
-    ctx->sched.wait (start_count, *task_count);
+    if (task_count->load (memory_order_acquire) > start_count)
+    {
+      phase_unlock u (*ctx, phase);
+      ctx->sched.wait (start_count, *task_count);
+    }
+
     task_count = nullptr;
   }
 }
-- 
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