/* Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. Stockfish is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . */ #include #include #include "movegen.h" #include "search.h" #include "thread.h" #include "ucioption.h" using namespace Search; ThreadsManager Threads; // Global object namespace { extern "C" { // start_routine() is the C function which is called when a new thread // is launched. It is a wrapper to member function pointed by start_fn. long start_routine(Thread* th) { (th->*(th->start_fn))(); return 0; } } } // Thread c'tor starts a newly-created thread of execution that will call // the idle loop function pointed by start_fn going immediately to sleep. Thread::Thread(Fn fn) { is_searching = do_exit = false; maxPly = splitPointsCnt = 0; curSplitPoint = NULL; start_fn = fn; threadID = Threads.size(); do_sleep = (fn != &Thread::main_loop); // Avoid a race with start_searching() lock_init(sleepLock); cond_init(sleepCond); for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++) lock_init(splitPoints[j].lock); if (!thread_create(handle, start_routine, this)) { std::cerr << "Failed to create thread number " << threadID << std::endl; ::exit(EXIT_FAILURE); } } // Thread d'tor waits for thread termination before to return. Thread::~Thread() { assert(do_sleep); do_exit = true; // Search must be already finished wake_up(); thread_join(handle); // Wait for thread termination lock_destroy(sleepLock); cond_destroy(sleepCond); for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++) lock_destroy(splitPoints[j].lock); } // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and // then calls check_time(). If maxPly is 0 thread sleeps until is woken up. extern void check_time(); void Thread::timer_loop() { while (!do_exit) { lock_grab(sleepLock); timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX); lock_release(sleepLock); check_time(); } } // Thread::main_loop() is where the main thread is parked waiting to be started // when there is a new search. Main thread will launch all the slave threads. void Thread::main_loop() { while (true) { lock_grab(sleepLock); do_sleep = true; // Always return to sleep after a search is_searching = false; while (do_sleep && !do_exit) { cond_signal(Threads.sleepCond); // Wake up UI thread if needed cond_wait(sleepCond, sleepLock); } lock_release(sleepLock); if (do_exit) return; is_searching = true; Search::think(); } } // Thread::wake_up() wakes up the thread, normally at the beginning of the search // or, if "sleeping threads" is used at split time. void Thread::wake_up() { lock_grab(sleepLock); cond_signal(sleepCond); lock_release(sleepLock); } // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is // reached while the program is pondering. The point is to work around a wrinkle // in the UCI protocol: When pondering, the engine is not allowed to give a // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply // wait here until one of these commands (that raise StopRequest) is sent and // then return, after which the bestmove and pondermove will be printed. void Thread::wait_for_stop_or_ponderhit() { Signals.stopOnPonderhit = true; lock_grab(sleepLock); while (!Signals.stop) cond_wait(sleepCond, sleepLock); lock_release(sleepLock); } // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the // current active split point, or in some ancestor of the split point. bool Thread::cutoff_occurred() const { for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent) if (sp->cutoff) return true; return false; } // Thread::is_available_to() checks whether the thread is available to help the // thread with threadID "master" at a split point. An obvious requirement is that // thread must be idle. With more than two threads, this is not sufficient: If // the thread is the master of some active split point, it is only available as a // slave to the threads 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::is_available_to(int master) const { if (is_searching) return false; // Make a local copy to be sure doesn't become zero under our feet while // testing next condition and so leading to an out of bound access. int spCnt = splitPointsCnt; // No active split points means that the thread is available as a slave for any // other thread otherwise apply the "helpful master" concept if possible. return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master)); } // init() is called at startup. Initializes lock and condition variable and // launches requested threads sending them immediately to sleep. We cannot use // a c'tor becuase Threads is a static object and we need a fully initialized // engine at this point due to allocation of endgames in Thread c'tor. void ThreadsManager::init() { cond_init(sleepCond); lock_init(splitLock); timer = new Thread(&Thread::timer_loop); threads.push_back(new Thread(&Thread::main_loop)); read_uci_options(); } // d'tor cleanly terminates the threads when the program exits. ThreadsManager::~ThreadsManager() { for (int i = 0; i < size(); i++) delete threads[i]; delete timer; lock_destroy(splitLock); cond_destroy(sleepCond); } // read_uci_options() updates internal threads parameters from the corresponding // UCI options and creates/destroys threads to match the requested number. Thread // objects are dynamically allocated to avoid creating in advance all possible // threads, with included pawns and material tables, if only few are used. void ThreadsManager::read_uci_options() { maxThreadsPerSplitPoint = Options["Max Threads per Split Point"]; minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY; useSleepingThreads = Options["Use Sleeping Threads"]; int requested = Options["Threads"]; assert(requested > 0); while (size() < requested) threads.push_back(new Thread(&Thread::idle_loop)); while (size() > requested) { delete threads.back(); threads.pop_back(); } } // wake_up() is called before a new search to start the threads that are waiting // on the sleep condition and to reset maxPly. When useSleepingThreads is set // threads will be woken up at split time. void ThreadsManager::wake_up() const { for (int i = 0; i < size(); i++) { threads[i]->maxPly = 0; threads[i]->do_sleep = false; if (!useSleepingThreads) threads[i]->wake_up(); } } // sleep() is called after the search finishes to ask all the threads but the // main one to go waiting on a sleep condition. void ThreadsManager::sleep() const { for (int i = 1; i < size(); i++) // Main thread will go to sleep by itself threads[i]->do_sleep = true; // to avoid a race with start_searching() } // available_slave_exists() tries to find an idle thread which is available as // a slave for the thread with threadID 'master'. bool ThreadsManager::available_slave_exists(int master) const { assert(master >= 0 && master < size()); for (int i = 0; i < size(); i++) if (threads[i]->is_available_to(master)) return true; return false; } // split() does the actual work of distributing the work at a node between // several available threads. If it does not succeed in splitting the node // (because no idle threads are available, or because we have no unused split // point objects), the function immediately returns. If splitting is possible, a // SplitPoint object is initialized with all the data that must be copied to the // helper threads and then helper threads are told that they have been assigned // work. This will cause them to instantly leave their idle loops and call // search(). When all threads have returned from search() then split() returns. template Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta, Value bestValue, Move* bestMove, Depth depth, Move threatMove, int moveCount, MovePicker* mp, int nodeType) { assert(pos.pos_is_ok()); assert(bestValue > -VALUE_INFINITE); assert(bestValue <= alpha); assert(alpha < beta); assert(beta <= VALUE_INFINITE); assert(depth > DEPTH_ZERO); int master = pos.thread(); Thread& masterThread = *threads[master]; if (masterThread.splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD) return bestValue; // Pick the next available split point from the split point stack SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt++]; sp->parent = masterThread.curSplitPoint; sp->master = master; sp->cutoff = false; sp->slavesMask = 1ULL << master; sp->depth = depth; sp->bestMove = *bestMove; sp->threatMove = threatMove; sp->alpha = alpha; sp->beta = beta; sp->nodeType = nodeType; sp->bestValue = bestValue; sp->mp = mp; sp->moveCount = moveCount; sp->pos = &pos; sp->nodes = 0; sp->ss = ss; assert(masterThread.is_searching); masterThread.curSplitPoint = sp; int slavesCnt = 0; // Try to allocate available threads and ask them to start searching setting // is_searching flag. This must be done under lock protection to avoid concurrent // allocation of the same slave by another master. lock_grab(sp->lock); lock_grab(splitLock); for (int i = 0; i < size() && !Fake; ++i) if (threads[i]->is_available_to(master)) { sp->slavesMask |= 1ULL << i; threads[i]->curSplitPoint = sp; threads[i]->is_searching = true; // Slave leaves idle_loop() if (useSleepingThreads) threads[i]->wake_up(); if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included break; } lock_release(splitLock); lock_release(sp->lock); // Everything is set up. The master thread enters the idle loop, from which // it will instantly launch a search, because its is_searching flag is set. // We pass the split point as a parameter to the idle loop, which means that // the thread will return from the idle loop when all slaves have finished // their work at this split point. if (slavesCnt || Fake) { masterThread.idle_loop(sp); // In helpful master concept a master can help only a sub-tree of its split // point, and because here is all finished is not possible master is booked. assert(!masterThread.is_searching); } // We have returned from the idle loop, which means that all threads are // finished. Note that setting is_searching and decreasing splitPointsCnt is // done under lock protection to avoid a race with Thread::is_available_to(). lock_grab(sp->lock); // To protect sp->nodes lock_grab(splitLock); masterThread.is_searching = true; masterThread.splitPointsCnt--; masterThread.curSplitPoint = sp->parent; pos.set_nodes_searched(pos.nodes_searched() + sp->nodes); *bestMove = sp->bestMove; lock_release(splitLock); lock_release(sp->lock); return sp->bestValue; } // Explicit template instantiations template Value ThreadsManager::split(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int); template Value ThreadsManager::split(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int); // ThreadsManager::set_timer() is used to set the timer to trigger after msec // milliseconds. If msec is 0 then timer is stopped. void ThreadsManager::set_timer(int msec) { lock_grab(timer->sleepLock); timer->maxPly = msec; cond_signal(timer->sleepCond); // Wake up and restart the timer lock_release(timer->sleepLock); } // ThreadsManager::wait_for_search_finished() waits for main thread to go to // sleep, this means search is finished. Then returns. void ThreadsManager::wait_for_search_finished() { Thread* main = threads[0]; lock_grab(main->sleepLock); cond_signal(main->sleepCond); // In case is waiting for stop or ponderhit while (!main->do_sleep) cond_wait(sleepCond, main->sleepLock); lock_release(main->sleepLock); } // ThreadsManager::start_searching() wakes up the main thread sleeping in // main_loop() so to start a new search, then returns immediately. void ThreadsManager::start_searching(const Position& pos, const LimitsType& limits, const std::vector& searchMoves) { wait_for_search_finished(); SearchTime.restart(); // As early as possible Signals.stopOnPonderhit = Signals.firstRootMove = false; Signals.stop = Signals.failedLowAtRoot = false; RootPosition.copy(pos, 0); Limits = limits; RootMoves.clear(); for (MoveList ml(pos); !ml.end(); ++ml) if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move())) RootMoves.push_back(RootMove(ml.move())); threads[0]->do_sleep = false; threads[0]->wake_up(); }