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;
233 threads[i]->maxPly = 0;
235 if (!useSleepingThreads)
236 threads[i]->wake_up();
241 // sleep() is called after the search to ask all the threads but the main to go
242 // waiting on a sleep condition.
244 void ThreadsManager::sleep() {
246 for (int i = 1; i < size(); i++) // Main thread will go to sleep by itself
247 threads[i]->do_sleep = true; // to avoid a race with start_thinking()
251 // init() is called during startup. Initializes locks and condition variables
252 // and launches all threads sending them immediately to sleep.
254 void ThreadsManager::init() {
256 cond_init(sleepCond);
257 lock_init(splitLock);
258 timer = new Thread(&Thread::timer_loop);
259 threads.push_back(new Thread(&Thread::main_loop));
264 // exit() is called to cleanly terminate the threads before the program finishes
266 void ThreadsManager::exit() {
268 for (int i = 0; i < size(); i++)
272 lock_destroy(splitLock);
273 cond_destroy(sleepCond);
277 // available_slave_exists() tries to find an idle thread which is available as
278 // a slave for the thread with threadID 'master'.
280 bool ThreadsManager::available_slave_exists(int master) const {
282 assert(master >= 0 && master < size());
284 for (int i = 0; i < size(); i++)
285 if (threads[i]->is_available_to(master))
292 // split() does the actual work of distributing the work at a node between
293 // several available threads. If it does not succeed in splitting the node
294 // (because no idle threads are available, or because we have no unused split
295 // point objects), the function immediately returns. If splitting is possible, a
296 // SplitPoint object is initialized with all the data that must be copied to the
297 // helper threads and then helper threads are told that they have been assigned
298 // work. This will cause them to instantly leave their idle loops and call
299 // search(). When all threads have returned from search() then split() returns.
302 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
303 Value bestValue, Move* bestMove, Depth depth,
304 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
305 assert(pos.pos_is_ok());
306 assert(bestValue > -VALUE_INFINITE);
307 assert(bestValue <= alpha);
308 assert(alpha < beta);
309 assert(beta <= VALUE_INFINITE);
310 assert(depth > DEPTH_ZERO);
312 int master = pos.thread();
313 Thread& masterThread = *threads[master];
315 if (masterThread.splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
318 // Pick the next available split point from the split point stack
319 SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt++];
321 sp->parent = masterThread.curSplitPoint;
324 sp->slavesMask = 1ULL << master;
326 sp->bestMove = *bestMove;
327 sp->threatMove = threatMove;
330 sp->nodeType = nodeType;
331 sp->bestValue = bestValue;
333 sp->moveCount = moveCount;
338 assert(masterThread.is_searching);
340 masterThread.curSplitPoint = sp;
343 // Try to allocate available threads and ask them to start searching setting
344 // is_searching flag. This must be done under lock protection to avoid concurrent
345 // allocation of the same slave by another master.
347 lock_grab(splitLock);
349 for (int i = 0; i < size() && !Fake; ++i)
350 if (threads[i]->is_available_to(master))
352 sp->slavesMask |= 1ULL << i;
353 threads[i]->curSplitPoint = sp;
354 threads[i]->is_searching = true; // Slave leaves idle_loop()
356 if (useSleepingThreads)
357 threads[i]->wake_up();
359 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
363 lock_release(splitLock);
364 lock_release(sp->lock);
366 // Everything is set up. The master thread enters the idle loop, from which
367 // it will instantly launch a search, because its is_searching flag is set.
368 // We pass the split point as a parameter to the idle loop, which means that
369 // the thread will return from the idle loop when all slaves have finished
370 // their work at this split point.
371 if (slavesCnt || Fake)
373 masterThread.idle_loop(sp);
375 // In helpful master concept a master can help only a sub-tree of its split
376 // point, and because here is all finished is not possible master is booked.
377 assert(!masterThread.is_searching);
380 // We have returned from the idle loop, which means that all threads are
381 // finished. Note that setting is_searching and decreasing splitPointsCnt is
382 // done under lock protection to avoid a race with Thread::is_available_to().
383 lock_grab(sp->lock); // To protect sp->nodes
384 lock_grab(splitLock);
386 masterThread.is_searching = true;
387 masterThread.splitPointsCnt--;
388 masterThread.curSplitPoint = sp->parent;
389 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
390 *bestMove = sp->bestMove;
392 lock_release(splitLock);
393 lock_release(sp->lock);
395 return sp->bestValue;
398 // Explicit template instantiations
399 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
400 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
403 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
404 // milliseconds. If msec is 0 then timer is stopped.
406 void ThreadsManager::set_timer(int msec) {
408 lock_grab(timer->sleepLock);
409 timer->maxPly = msec;
410 cond_signal(timer->sleepCond); // Wake up and restart the timer
411 lock_release(timer->sleepLock);
415 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
416 // thread parked in main_loop() and starting a new search. If asyncMode is true
417 // then function returns immediately, otherwise caller is blocked waiting for
418 // the search to finish.
420 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
421 const std::set<Move>& searchMoves, bool async) {
422 Thread& main = *threads.front();
424 lock_grab(main.sleepLock);
426 // Wait main thread has finished before to launch a new search
427 while (!main.do_sleep)
428 cond_wait(sleepCond, main.sleepLock);
430 // Copy input arguments to initialize the search
431 RootPosition.copy(pos, 0);
435 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
436 // set is given, with the subset of legal moves to search.
437 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
438 if (searchMoves.empty() || searchMoves.count(ml.move()))
439 RootMoves.push_back(RootMove(ml.move()));
441 // Reset signals before to start the new search
442 Signals.stopOnPonderhit = Signals.firstRootMove = false;
443 Signals.stop = Signals.failedLowAtRoot = false;
445 main.do_sleep = false;
446 cond_signal(main.sleepCond); // Wake up main thread and start searching
449 while (!main.do_sleep)
450 cond_wait(sleepCond, main.sleepLock);
452 lock_release(main.sleepLock);
456 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
457 // and to wait for the main thread finishing the search. Needed to wait exiting
458 // and terminate the threads after a 'quit' command.
460 void ThreadsManager::stop_thinking() {
462 Thread& main = *threads.front();
464 Search::Signals.stop = true;
466 lock_grab(main.sleepLock);
468 cond_signal(main.sleepCond); // In case is waiting for stop or ponderhit
470 while (!main.do_sleep)
471 cond_wait(sleepCond, main.sleepLock);
473 lock_release(main.sleepLock);