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();
53 do_sleep = (fn != &Thread::main_loop); // Avoid a race with start_thinking()
58 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
59 lock_init(splitPoints[j].lock);
61 if (!thread_create(handle, start_routine, this))
63 std::cerr << "Failed to create thread number " << threadID << std::endl;
69 // Thread d'tor waits for thread termination before to return.
75 do_exit = true; // Search must be already finished
78 thread_join(handle); // Wait for thread termination
80 lock_destroy(sleepLock);
81 cond_destroy(sleepCond);
83 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
84 lock_destroy(splitPoints[j].lock);
88 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
89 // then calls check_time(). If maxPly is 0 thread sleeps until is woken up.
90 extern void check_time();
92 void Thread::timer_loop() {
97 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
98 lock_release(sleepLock);
104 // Thread::main_loop() is where the main thread is parked waiting to be started
105 // when there is a new search. Main thread will launch all the slave threads.
107 void Thread::main_loop() {
111 lock_grab(sleepLock);
113 do_sleep = true; // Always return to sleep after a search
114 is_searching = false;
116 while (do_sleep && !do_exit)
118 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
119 cond_wait(sleepCond, sleepLock);
122 lock_release(sleepLock);
134 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
135 // or, if "sleeping threads" is used at split time.
137 void Thread::wake_up() {
139 lock_grab(sleepLock);
140 cond_signal(sleepCond);
141 lock_release(sleepLock);
145 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
146 // reached while the program is pondering. The point is to work around a wrinkle
147 // in the UCI protocol: When pondering, the engine is not allowed to give a
148 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
149 // wait here until one of these commands (that raise StopRequest) is sent and
150 // then return, after which the bestmove and pondermove will be printed.
152 void Thread::wait_for_stop_or_ponderhit() {
154 Signals.stopOnPonderhit = true;
156 lock_grab(sleepLock);
158 while (!Signals.stop)
159 cond_wait(sleepCond, sleepLock);
161 lock_release(sleepLock);
165 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
166 // current active split point, or in some ancestor of the split point.
168 bool Thread::cutoff_occurred() const {
170 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
178 // Thread::is_available_to() checks whether the thread is available to help the
179 // thread with threadID "master" at a split point. An obvious requirement is that
180 // thread must be idle. With more than two threads, this is not sufficient: If
181 // the thread is the master of some active split point, it is only available as a
182 // slave to the threads which are busy searching the split point at the top of
183 // "slave"'s split point stack (the "helpful master concept" in YBWC terminology).
185 bool Thread::is_available_to(int master) const {
190 // Make a local copy to be sure doesn't become zero under our feet while
191 // testing next condition and so leading to an out of bound access.
192 int spCnt = splitPointsCnt;
194 // No active split points means that the thread is available as a slave for any
195 // other thread otherwise apply the "helpful master" concept if possible.
196 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master));
200 // init() is called at startup. Initializes lock and condition variable and
201 // launches requested threads sending them immediately to sleep. We cannot use
202 // a c'tor becuase Threads is a static object and we need a fully initialized
203 // engine at this point due to allocation of endgames in Thread c'tor.
205 void ThreadsManager::init() {
207 cond_init(sleepCond);
208 lock_init(splitLock);
209 timer = new Thread(&Thread::timer_loop);
210 threads.push_back(new Thread(&Thread::main_loop));
215 // d'tor cleanly terminates the threads when the program exits.
217 ThreadsManager::~ThreadsManager() {
219 for (int i = 0; i < size(); i++)
223 lock_destroy(splitLock);
224 cond_destroy(sleepCond);
228 // read_uci_options() updates internal threads parameters from the corresponding
229 // UCI options and creates/destroys threads to match the requested number. Thread
230 // objects are dynamically allocated to avoid creating in advance all possible
231 // threads, with included pawns and material tables, if only few are used.
233 void ThreadsManager::read_uci_options() {
235 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
236 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
237 useSleepingThreads = Options["Use Sleeping Threads"];
238 int requested = Options["Threads"];
240 assert(requested > 0);
242 while (size() < requested)
243 threads.push_back(new Thread(&Thread::idle_loop));
245 while (size() > requested)
247 delete threads.back();
253 // wake_up() is called before a new search to start the threads that are waiting
254 // on the sleep condition and to reset maxPly. When useSleepingThreads is set
255 // threads will be woken up at split time.
257 void ThreadsManager::wake_up() const {
259 for (int i = 0; i < size(); i++)
261 threads[i]->do_sleep = false;
262 threads[i]->maxPly = 0;
264 if (!useSleepingThreads)
265 threads[i]->wake_up();
270 // sleep() is called after the search finishes to ask all the threads but the
271 // main one to go waiting on a sleep condition.
273 void ThreadsManager::sleep() const {
275 for (int i = 1; i < size(); i++) // Main thread will go to sleep by itself
276 threads[i]->do_sleep = true; // to avoid a race with start_thinking()
280 // available_slave_exists() tries to find an idle thread which is available as
281 // a slave for the thread with threadID 'master'.
283 bool ThreadsManager::available_slave_exists(int master) const {
285 assert(master >= 0 && master < size());
287 for (int i = 0; i < size(); i++)
288 if (threads[i]->is_available_to(master))
295 // split() does the actual work of distributing the work at a node between
296 // several available threads. If it does not succeed in splitting the node
297 // (because no idle threads are available, or because we have no unused split
298 // point objects), the function immediately returns. If splitting is possible, a
299 // SplitPoint object is initialized with all the data that must be copied to the
300 // helper threads and then helper threads are told that they have been assigned
301 // work. This will cause them to instantly leave their idle loops and call
302 // search(). When all threads have returned from search() then split() returns.
305 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
306 Value bestValue, Move* bestMove, Depth depth,
307 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
308 assert(pos.pos_is_ok());
309 assert(bestValue > -VALUE_INFINITE);
310 assert(bestValue <= alpha);
311 assert(alpha < beta);
312 assert(beta <= VALUE_INFINITE);
313 assert(depth > DEPTH_ZERO);
315 int master = pos.thread();
316 Thread& masterThread = *threads[master];
318 if (masterThread.splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
321 // Pick the next available split point from the split point stack
322 SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt++];
324 sp->parent = masterThread.curSplitPoint;
327 sp->slavesMask = 1ULL << master;
329 sp->bestMove = *bestMove;
330 sp->threatMove = threatMove;
333 sp->nodeType = nodeType;
334 sp->bestValue = bestValue;
336 sp->moveCount = moveCount;
341 assert(masterThread.is_searching);
343 masterThread.curSplitPoint = sp;
346 // Try to allocate available threads and ask them to start searching setting
347 // is_searching flag. This must be done under lock protection to avoid concurrent
348 // allocation of the same slave by another master.
350 lock_grab(splitLock);
352 for (int i = 0; i < size() && !Fake; ++i)
353 if (threads[i]->is_available_to(master))
355 sp->slavesMask |= 1ULL << i;
356 threads[i]->curSplitPoint = sp;
357 threads[i]->is_searching = true; // Slave leaves idle_loop()
359 if (useSleepingThreads)
360 threads[i]->wake_up();
362 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
366 lock_release(splitLock);
367 lock_release(sp->lock);
369 // Everything is set up. The master thread enters the idle loop, from which
370 // it will instantly launch a search, because its is_searching flag is set.
371 // We pass the split point as a parameter to the idle loop, which means that
372 // the thread will return from the idle loop when all slaves have finished
373 // their work at this split point.
374 if (slavesCnt || Fake)
376 masterThread.idle_loop(sp);
378 // In helpful master concept a master can help only a sub-tree of its split
379 // point, and because here is all finished is not possible master is booked.
380 assert(!masterThread.is_searching);
383 // We have returned from the idle loop, which means that all threads are
384 // finished. Note that setting is_searching and decreasing splitPointsCnt is
385 // done under lock protection to avoid a race with Thread::is_available_to().
386 lock_grab(sp->lock); // To protect sp->nodes
387 lock_grab(splitLock);
389 masterThread.is_searching = true;
390 masterThread.splitPointsCnt--;
391 masterThread.curSplitPoint = sp->parent;
392 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
393 *bestMove = sp->bestMove;
395 lock_release(splitLock);
396 lock_release(sp->lock);
398 return sp->bestValue;
401 // Explicit template instantiations
402 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
403 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
406 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
407 // milliseconds. If msec is 0 then timer is stopped.
409 void ThreadsManager::set_timer(int msec) {
411 lock_grab(timer->sleepLock);
412 timer->maxPly = msec;
413 cond_signal(timer->sleepCond); // Wake up and restart the timer
414 lock_release(timer->sleepLock);
418 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
419 // thread parked in main_loop() and starting a new search. If async is true
420 // then function returns immediately, otherwise caller is blocked waiting for
421 // the search to finish.
423 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
424 const std::set<Move>& searchMoves, bool async) {
425 Thread& main = *threads.front();
427 lock_grab(main.sleepLock);
429 while (!main.do_sleep)
430 cond_wait(sleepCond, main.sleepLock); // Wait main thread has finished
432 Signals.stopOnPonderhit = Signals.firstRootMove = false;
433 Signals.stop = Signals.failedLowAtRoot = false;
435 RootPosition.copy(pos, 0);
439 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
440 if (searchMoves.empty() || searchMoves.count(ml.move()))
441 RootMoves.push_back(RootMove(ml.move()));
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. We cannot return before
456 // main has finished to avoid a crash in case of 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);