Use acquire() and release() for spinlocks

[stockfish] / src / thread.h

diff --git a/src/thread.h b/src/thread.h
index 4d70bf2fbd038a9da98971c04c1bada7ba523743..7932ad45f6b0e967229b6557f69858a3abd94fcf 100644 (file)
--- a/src/thread.h
+++ b/src/thread.h
@@ -40,6 +40,20 @@ const size_t MAX_THREADS = 128;
 const size_t MAX_SPLITPOINTS_PER_THREAD = 8;
 const size_t MAX_SLAVES_PER_SPLITPOINT = 4;
 
+class Spinlock {
+
+  std::atomic_int lock;
+
+public:
+  Spinlock() { lock = 1; } // Init here to workaround a bug with MSVC 2013
+  void acquire() {
+      while (lock.fetch_sub(1, std::memory_order_acquire) != 1)
+          for (int cnt = 0; lock.load(std::memory_order_relaxed) <= 0; ++cnt)
+              if (cnt >= 10000) std::this_thread::yield(); // Be nice to hyperthreading
+  }
+  void release() { lock.store(1, std::memory_order_release); }
+};
+
 
 /// SplitPoint struct stores information shared by the threads searching in
 /// parallel below the same split point. It is populated at splitting time.
@@ -60,7 +74,7 @@ struct SplitPoint {
   SplitPoint* parentSplitPoint;
 
   // Shared variable data
-  Mutex mutex;
+  Spinlock spinlock;
   std::bitset<MAX_THREADS> slavesMask;
   volatile bool allSlavesSearching;
   volatile uint64_t nodes;
@@ -84,6 +98,7 @@ struct ThreadBase {
 
   std::thread nativeThread;
   Mutex mutex;
+  Spinlock spinlock;
   ConditionVariable sleepCondition;
   volatile bool exit = false;
 };