Use spinlock instead of mutex for Threads and SplitPoint

[stockfish] / src / thread.cpp

diff --git a/src/thread.cpp b/src/thread.cpp
index c232b849babacc66ef6e262322678b18883a37e5..1217e3ab020656787c9dd1b8a5886fecdadcaa1a 100644 (file)
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -81,7 +81,8 @@ void ThreadBase::wait_for(volatile const bool& condition) {
 Thread::Thread() /* : splitPoints() */ { // Initialization of non POD broken in MSVC
 
   searching = false;
-  maxPly = splitPointsSize = 0;
+  maxPly = 0;
+  splitPointsSize = 0;
   activeSplitPoint = nullptr;
   activePosition = nullptr;
   idx = Threads.size(); // Starts from 0
@@ -115,7 +116,7 @@ bool Thread::available_to(const Thread* master) const {
 
   // Make a local copy to be sure it doesn't become zero under our feet while
   // testing next condition and so leading to an out of bounds access.
-  const int size = splitPointsSize;
+  const size_t size = splitPointsSize;
 
   // No split points means that the thread is available as a slave for any
   // other thread otherwise apply the "helpful master" concept if possible.
@@ -144,7 +145,7 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
   // Pick and init the next available split point
   SplitPoint& sp = splitPoints[splitPointsSize];
 
-  sp.masterThread = this;
+  sp.master = this;
   sp.parentSplitPoint = activeSplitPoint;
   sp.slavesMask = 0, sp.slavesMask.set(idx);
   sp.depth = depth;
@@ -164,8 +165,8 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
   // Try to allocate available threads and ask them to start searching setting
   // 'searching' flag. This must be done under lock protection to avoid concurrent
   // allocation of the same slave by another master.
-  Threads.mutex.lock();
-  sp.mutex.lock();
+  Threads.spinlock.acquire();
+  sp.spinlock.acquire();
 
   sp.allSlavesSearching = true; // Must be set under lock protection
   ++splitPointsSize;
@@ -174,7 +175,8 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
 
   Thread* slave;
 
-  while ((slave = Threads.available_slave(this)) != nullptr)
+  while (    sp.slavesMask.count() < MAX_SLAVES_PER_SPLITPOINT
+         && (slave = Threads.available_slave(this)) != nullptr)
   {
       sp.slavesMask.set(slave->idx);
       slave->activeSplitPoint = &sp;
@@ -186,8 +188,8 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
   // it will instantly launch a search, because its 'searching' flag is set.
   // The thread will return from the idle loop when all slaves have finished
   // their work at this split point.
-  sp.mutex.unlock();
-  Threads.mutex.unlock();
+  sp.spinlock.release();
+  Threads.spinlock.release();
 
   Thread::idle_loop(); // Force a call to base class idle_loop()
 
@@ -200,8 +202,8 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
   // We have returned from the idle loop, which means that all threads are
   // finished. Note that setting 'searching' and decreasing splitPointsSize must
   // be done under lock protection to avoid a race with Thread::available_to().
-  Threads.mutex.lock();
-  sp.mutex.lock();
+  Threads.spinlock.acquire();
+  sp.spinlock.acquire();
 
   searching = true;
   --splitPointsSize;
@@ -211,8 +213,8 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
   *bestMove = sp.bestMove;
   *bestValue = sp.bestValue;
 
-  sp.mutex.unlock();
-  Threads.mutex.unlock();
+  sp.spinlock.release();
+  Threads.spinlock.release();
 }
 
 
@@ -365,10 +367,10 @@ void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
       assert(!states.get());
   }
 
-  for (const ExtMove& ms : MoveList<LEGAL>(pos))
+  for (const auto& m : MoveList<LEGAL>(pos))
       if (   limits.searchmoves.empty()
-          || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), ms.move))
-          RootMoves.push_back(RootMove(ms.move));
+          || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
+          RootMoves.push_back(RootMove(m));
 
   main()->thinking = true;
   main()->notify_one(); // Starts main thread