Use acquire() and release() for spinlocks

[stockfish] / src / thread.h

diff --git a/src/thread.h b/src/thread.h
index 0469dc1d70fa180cfe17ca6a38e1c7a733b1ba28..7932ad45f6b0e967229b6557f69858a3abd94fcf 100644 (file)
--- a/src/thread.h
+++ b/src/thread.h
@@ -40,16 +40,18 @@ const size_t MAX_THREADS = 128;
 const size_t MAX_SPLITPOINTS_PER_THREAD = 8;
 const size_t MAX_SLAVES_PER_SPLITPOINT = 4;
 
-
-/// Spinlock class wraps low level atomic operations to provide a spin lock
-
 class Spinlock {
 
-  Mutex m; // WARNING: Diasabled spinlocks to test on fishtest
+  std::atomic_int lock;
 
 public:
-  void acquire() { m.lock(); }
-  void release() { m.unlock(); }
+  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); }
 };
 
 
@@ -96,6 +98,7 @@ struct ThreadBase {
 
   std::thread nativeThread;
   Mutex mutex;
+  Spinlock spinlock;
   ConditionVariable sleepCondition;
   volatile bool exit = false;
 };
@@ -163,7 +166,6 @@ struct ThreadPool : public std::vector<Thread*> {
   void start_thinking(const Position&, const Search::LimitsType&, Search::StateStackPtr&);
 
   Depth minimumSplitDepth;
-  Spinlock spinlock;
   ConditionVariable sleepCondition;
   TimerThread* timer;
 };