2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
26 #include "ucioption.h"
28 using namespace Search;
30 ThreadsManager Threads; // Global object
32 namespace { extern "C" {
34 // start_routine() is the C function which is called when a new thread
35 // is launched. It is a wrapper to member function pointed by start_fn
37 long start_routine(Thread* th) { (th->*(th->start_fn))(); return 0; }
42 // Thread c'tor starts a newly-created thread of execution that will call
43 // the idle loop function pointed by start_fn going immediately to sleep.
45 Thread::Thread(Fn fn) {
47 is_searching = do_exit = false;
48 maxPly = splitPointsCnt = 0;
51 threadID = Threads.size();
52 do_sleep = (threadID != 0); // Avoid a race with start_thinking()
57 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
58 lock_init(splitPoints[j].lock);
60 if (!thread_create(handle, start_routine, this))
62 std::cerr << "Failed to create thread number " << threadID << std::endl;
68 // Thread d'tor will wait for thread termination before to return.
74 do_exit = true; // Search must be already finished
77 thread_join(handle); // Wait for thread termination
79 lock_destroy(sleepLock);
80 cond_destroy(sleepCond);
82 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
83 lock_destroy(splitPoints[j].lock);
87 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
88 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
89 extern void check_time();
91 void Thread::timer_loop() {
96 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
97 lock_release(sleepLock);
103 // Thread::main_loop() is where the main thread is parked waiting to be started
104 // when there is a new search. Main thread will launch all the slave threads.
106 void Thread::main_loop() {
110 lock_grab(sleepLock);
112 do_sleep = true; // Always return to sleep after a search
113 is_searching = false;
115 while (do_sleep && !do_exit)
117 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
118 cond_wait(sleepCond, sleepLock);
121 lock_release(sleepLock);
133 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
134 // or, if "sleeping threads" is used, when there is some work to do.
136 void Thread::wake_up() {
138 lock_grab(sleepLock);
139 cond_signal(sleepCond);
140 lock_release(sleepLock);
144 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
145 // reached while the program is pondering. The point is to work around a wrinkle
146 // in the UCI protocol: When pondering, the engine is not allowed to give a
147 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
148 // wait here until one of these commands (that raise StopRequest) is sent and
149 // then return, after which the bestmove and pondermove will be printed.
151 void Thread::wait_for_stop_or_ponderhit() {
153 Signals.stopOnPonderhit = true;
155 lock_grab(sleepLock);
157 while (!Signals.stop)
158 cond_wait(sleepCond, sleepLock);
160 lock_release(sleepLock);
164 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
165 // active split point, or in some ancestor of the split point.
167 bool Thread::cutoff_occurred() const {
169 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
177 // is_available_to() checks whether the thread is available to help the thread with
178 // threadID "master" at a split point. An obvious requirement is that thread must be
179 // idle. With more than two threads, this is not by itself sufficient: If the thread
180 // is the master of some active split point, it is only available as a slave to the
181 // threads which are busy searching the split point at the top of "slave"'s split
182 // point stack (the "helpful master concept" in YBWC terminology).
184 bool Thread::is_available_to(int master) const {
189 // Make a local copy to be sure doesn't become zero under our feet while
190 // testing next condition and so leading to an out of bound access.
191 int spCnt = splitPointsCnt;
193 // No active split points means that the thread is available as a slave for any
194 // other thread otherwise apply the "helpful master" concept if possible.
195 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master));
199 // read_uci_options() updates internal threads parameters from the corresponding
200 // UCI options and creates/destroys threads to match the requested number. Thread
201 // objects are dynamically allocated to avoid creating in advance all possible
202 // threads, with included pawns and material tables, if only few are used.
204 void ThreadsManager::read_uci_options() {
206 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
207 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
208 useSleepingThreads = Options["Use Sleeping Threads"];
209 int requested = Options["Threads"];
211 assert(requested > 0);
213 while (size() < requested)
214 threads.push_back(new Thread(&Thread::idle_loop));
216 while (size() > requested)
218 delete threads.back();
224 // wake_up() is called before a new search to start the threads that are waiting
225 // on the sleep condition. If useSleepingThreads is set threads will be woken up
228 void ThreadsManager::wake_up() {
230 for (int i = 0; i < size(); i++)
232 threads[i]->do_sleep = false;
234 if (!useSleepingThreads)
235 threads[i]->wake_up();
240 // sleep() is called after the search to ask threads to wait on sleep condition
242 void ThreadsManager::sleep() {
244 for (int i = 0; i < size(); i++)
245 threads[i]->do_sleep = true;
249 // init() is called during startup. Initializes locks and condition variables
250 // and launches all threads sending them immediately to sleep.
252 void ThreadsManager::init() {
254 cond_init(sleepCond);
255 lock_init(splitLock);
256 timer = new Thread(&Thread::timer_loop);
257 threads.push_back(new Thread(&Thread::main_loop));
262 // exit() is called to cleanly terminate the threads before the program finishes
264 void ThreadsManager::exit() {
266 for (int i = 0; i < size(); i++)
270 lock_destroy(splitLock);
271 cond_destroy(sleepCond);
275 // available_slave_exists() tries to find an idle thread which is available as
276 // a slave for the thread with threadID 'master'.
278 bool ThreadsManager::available_slave_exists(int master) const {
280 assert(master >= 0 && master < size());
282 for (int i = 0; i < size(); i++)
283 if (threads[i]->is_available_to(master))
290 // split() does the actual work of distributing the work at a node between
291 // several available threads. If it does not succeed in splitting the node
292 // (because no idle threads are available, or because we have no unused split
293 // point objects), the function immediately returns. If splitting is possible, a
294 // SplitPoint object is initialized with all the data that must be copied to the
295 // helper threads and then helper threads are told that they have been assigned
296 // work. This will cause them to instantly leave their idle loops and call
297 // search(). When all threads have returned from search() then split() returns.
300 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
301 Value bestValue, Move* bestMove, Depth depth,
302 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
303 assert(pos.pos_is_ok());
304 assert(bestValue > -VALUE_INFINITE);
305 assert(bestValue <= alpha);
306 assert(alpha < beta);
307 assert(beta <= VALUE_INFINITE);
308 assert(depth > DEPTH_ZERO);
310 int master = pos.thread();
311 Thread& masterThread = *threads[master];
313 if (masterThread.splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
316 // Pick the next available split point from the split point stack
317 SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt++];
319 sp->parent = masterThread.curSplitPoint;
322 sp->slavesMask = 1ULL << master;
324 sp->bestMove = *bestMove;
325 sp->threatMove = threatMove;
328 sp->nodeType = nodeType;
329 sp->bestValue = bestValue;
331 sp->moveCount = moveCount;
336 assert(masterThread.is_searching);
338 masterThread.curSplitPoint = sp;
341 // Try to allocate available threads and ask them to start searching setting
342 // is_searching flag. This must be done under lock protection to avoid concurrent
343 // allocation of the same slave by another master.
345 lock_grab(splitLock);
347 for (int i = 0; i < size() && !Fake; ++i)
348 if (threads[i]->is_available_to(master))
350 sp->slavesMask |= 1ULL << i;
351 threads[i]->curSplitPoint = sp;
352 threads[i]->is_searching = true; // Slave leaves idle_loop()
354 if (useSleepingThreads)
355 threads[i]->wake_up();
357 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
361 lock_release(splitLock);
362 lock_release(sp->lock);
364 // Everything is set up. The master thread enters the idle loop, from which
365 // it will instantly launch a search, because its is_searching flag is set.
366 // We pass the split point as a parameter to the idle loop, which means that
367 // the thread will return from the idle loop when all slaves have finished
368 // their work at this split point.
369 if (slavesCnt || Fake)
371 masterThread.idle_loop(sp);
373 // In helpful master concept a master can help only a sub-tree of its split
374 // point, and because here is all finished is not possible master is booked.
375 assert(!masterThread.is_searching);
378 // We have returned from the idle loop, which means that all threads are
379 // finished. Note that setting is_searching and decreasing splitPointsCnt is
380 // done under lock protection to avoid a race with Thread::is_available_to().
381 lock_grab(sp->lock); // To protect sp->nodes
382 lock_grab(splitLock);
384 masterThread.is_searching = true;
385 masterThread.splitPointsCnt--;
386 masterThread.curSplitPoint = sp->parent;
387 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
388 *bestMove = sp->bestMove;
390 lock_release(splitLock);
391 lock_release(sp->lock);
393 return sp->bestValue;
396 // Explicit template instantiations
397 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
398 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
401 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
402 // milliseconds. If msec is 0 then timer is stopped.
404 void ThreadsManager::set_timer(int msec) {
406 lock_grab(timer->sleepLock);
407 timer->maxPly = msec;
408 cond_signal(timer->sleepCond); // Wake up and restart the timer
409 lock_release(timer->sleepLock);
413 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
414 // thread parked in main_loop() and starting a new search. If asyncMode is true
415 // then function returns immediately, otherwise caller is blocked waiting for
416 // the search to finish.
418 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
419 const std::set<Move>& searchMoves, bool async) {
420 Thread& main = *threads.front();
422 lock_grab(main.sleepLock);
424 // Wait main thread has finished before to launch a new search
425 while (!main.do_sleep)
426 cond_wait(sleepCond, main.sleepLock);
428 // Copy input arguments to initialize the search
429 RootPosition.copy(pos, 0);
433 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
434 // set is given, with the subset of legal moves to search.
435 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
436 if (searchMoves.empty() || searchMoves.count(ml.move()))
437 RootMoves.push_back(RootMove(ml.move()));
439 // Reset signals before to start the new search
440 Signals.stopOnPonderhit = Signals.firstRootMove = false;
441 Signals.stop = Signals.failedLowAtRoot = false;
443 main.do_sleep = false;
444 cond_signal(main.sleepCond); // Wake up main thread and start searching
447 while (!main.do_sleep)
448 cond_wait(sleepCond, main.sleepLock);
450 lock_release(main.sleepLock);
454 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
455 // and to wait for the main thread finishing the search. Needed to wait exiting
456 // and terminate the threads after a 'quit' command.
458 void ThreadsManager::stop_thinking() {
460 Thread& main = *threads.front();
462 Search::Signals.stop = true;
464 lock_grab(main.sleepLock);
466 cond_signal(main.sleepCond); // In case is waiting for stop or ponderhit
468 while (!main.do_sleep)
469 cond_wait(sleepCond, main.sleepLock);
471 lock_release(main.sleepLock);