diff --git a/src/search.cpp b/src/search.cpp index fbe6b2c0..60d1a868 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -984,8 +984,10 @@ moves_loop: // When in check and at SpNode search starts from here // Step 19. Check for splitting the search if ( !SpNode + && Threads.size() >= 2 && depth >= Threads.minimumSplitDepth - && Threads.available_slave(thisThread) + && ( !thisThread->activeSplitPoint + || !thisThread->activeSplitPoint->allowLatejoin) && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD) { assert(bestValue > -VALUE_INFINITE && bestValue < beta); @@ -1527,9 +1529,9 @@ void Thread::idle_loop() { assert(searching); - searching = false; activePosition = NULL; sp->slavesMask.reset(idx); + sp->allowLatejoin = false; sp->nodes += pos.nodes_searched(); // Wake up the master thread so to allow it to return from the idle @@ -1547,6 +1549,10 @@ void Thread::idle_loop() { // the sp master. Also accessing other Thread objects is unsafe because // if we are exiting there is a chance that they are already freed. sp->mutex.unlock(); + + // Try to late join to another splitpoint + if (Threads.size() <= 2 || !attempt_to_latejoin()) // FIXME: attempt_to_latejoin() is theoretically unsafe when were are exiting the program... + searching = false; } // If this thread is the master of a split point and all slaves have finished @@ -1562,6 +1568,44 @@ void Thread::idle_loop() { } } +bool Thread::attempt_to_latejoin() +{ + SplitPoint *sp; + size_t i; + bool success = false; + + for (i = 0; i < Threads.size(); ++i) + { + int size = Threads[i]->splitPointsSize; // Make a local copy to prevent size from changing under our feet. + + sp = size ? &Threads[i]->splitPoints[size - 1] : NULL; + + if ( sp + && sp->allowLatejoin + && available_to(Threads[i], true)) + break; + } + + if (i == Threads.size()) + return false; // No suitable splitpoint found! + + // Recheck conditions under lock protection + Threads.mutex.lock(); + sp->mutex.lock(); + + if ( sp->allowLatejoin + && available_to(Threads[i], true)) + { + activeSplitPoint = sp; + sp->slavesMask.set(this->idx); + success = true; + } + + sp->mutex.unlock(); + Threads.mutex.unlock(); + + return success; +} /// check_time() is called by the timer thread when the timer triggers. It is /// used to print debug info and, more importantly, to detect when we are out of diff --git a/src/thread.cpp b/src/thread.cpp index 432d573d..f5aab2b1 100644 --- a/src/thread.cpp +++ b/src/thread.cpp @@ -112,9 +112,9 @@ bool Thread::cutoff_occurred() const { // which are busy searching the split point at the top of slave's split point // stack (the "helpful master concept" in YBWC terminology). -bool Thread::available_to(const Thread* master) const { +bool Thread::available_to(const Thread* master, bool latejoin) const { - if (searching) + if (searching && !latejoin) return false; // Make a local copy to be sure it doesn't become zero under our feet while @@ -239,7 +239,7 @@ void ThreadPool::read_uci_options() { Thread* ThreadPool::available_slave(const Thread* master) const { for (const_iterator it = begin(); it != end(); ++it) - if ((*it)->available_to(master)) + if ((*it)->available_to(master, false)) return *it; return NULL; @@ -292,6 +292,7 @@ void Thread::split(Position& pos, const Stack* ss, Value alpha, Value beta, Valu Threads.mutex.lock(); sp.mutex.lock(); + sp.allowLatejoin = true; // Only set this under lock protection ++splitPointsSize; activeSplitPoint = &sp; activePosition = NULL; diff --git a/src/thread.h b/src/thread.h index 44aa6883..edc4ee31 100644 --- a/src/thread.h +++ b/src/thread.h @@ -77,6 +77,7 @@ struct SplitPoint { // Shared data Mutex mutex; std::bitset slavesMask; + volatile bool allowLatejoin; volatile uint64_t nodes; volatile Value alpha; volatile Value bestValue; @@ -113,8 +114,9 @@ struct Thread : public ThreadBase { Thread(); virtual void idle_loop(); + bool attempt_to_latejoin(); bool cutoff_occurred() const; - bool available_to(const Thread* master) const; + bool available_to(const Thread* master, bool latejoin) const; template void split(Position& pos, const Search::Stack* ss, Value alpha, Value beta, Value* bestValue, Move* bestMove,