Fix race condition where idle_loop() gets called from Split()

[stockfish] / src / thread.cpp

diff --git a/src/thread.cpp b/src/thread.cpp
index f5b8b5e275aff3313b74ae061fd8b4455d98dab8..df746a4a825d2befdc77fa5397e0b5be952b3a65 100644 (file)
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -312,6 +312,7 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
       sp.mutex.unlock();
       Threads.mutex.unlock();
 
+      // Calling idle_loop with sp.mutex locked
       Thread::idle_loop(); // Force a call to base class idle_loop()
 
       // In helpful master concept a master can help only a sub-tree of its split
@@ -322,6 +323,10 @@ 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 is
       // done under lock protection to avoid a race with Thread::is_available_to().
+      // idle_loop returns with sp.mutex locked but we must unlock it inorder to
+      // lock Threads.mutex without conflicting with check_time() (threads holding 
+      // multiple locks must always acquired them in the same order to avoid deadlocks)
+      sp.mutex.unlock(); 
       Threads.mutex.lock();
       sp.mutex.lock();
   }
@@ -357,8 +362,8 @@ void ThreadPool::wait_for_think_finished() {
 // start_thinking() wakes up the main thread sleeping in MainThread::idle_loop()
 // so to start a new search, then returns immediately.
 
-void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
-                                const std::vector<Move>& searchMoves, StateStackPtr& states) {
+void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits, const std::vector<Move>& searchMoves,
+                                StateStackPtr& setupStates, MovesVectPtr& setupMoves) {
   wait_for_think_finished();
 
   SearchTime = Time::now(); // As early as possible
@@ -368,7 +373,8 @@ void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
 
   RootPos = pos;
   Limits = limits;
-  SetupStates = states; // Ownership transfer here
+  SetupStates = setupStates; // Ownership transfer here
+  SetupMoves = setupMoves;   // Ownership transfer here
   RootMoves.clear();
 
   for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)