Avoid locking/unlocking in a tight loop

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 19ebc5e6eeeb79ef8ce12a3835372b1581edae95..9a373dec456223cfbac60cd4ce8729adbf3d7a13 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1622,13 +1622,11 @@ void Thread::idle_loop() {
 
   // Pointer 'this_sp' is not null only if we are called from split(), and not
   // at the thread creation. So it means we are the split point's master.
-  const SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
+  SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
 
   assert(!this_sp || (this_sp->masterThread == this && searching));
 
-  // If this thread is the master of a split point and all slaves have finished
-  // their work at this split point, return from the idle loop.
-  while (!this_sp || this_sp->slavesMask)
+  while (true)
   {
       // If we are not searching, wait for a condition to be signaled instead of
       // wasting CPU time polling for work.
@@ -1721,6 +1719,17 @@ void Thread::idle_loop() {
           // unsafe because if we are exiting there is a chance are already freed.
           sp->mutex.unlock();
       }
+
+      // If this thread is the master of a split point and all slaves have finished
+      // their work at this split point, return from the idle loop.
+      if (this_sp && !this_sp->slavesMask)
+      {
+          this_sp->mutex.lock();
+          bool finished = !this_sp->slavesMask; // Retest under lock protection
+          this_sp->mutex.unlock();
+          if (finished)
+              return;
+      }
   }
 }