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 simply calls idle_loop() of the supplied thread. The first
36 // and last thread are special. First one is the main search thread while the
37 // last one mimics a timer, they run in main_loop() and timer_loop().
39 long start_routine(Thread* th) {
41 if (th->threadID == 0)
44 else if (th->threadID == MAX_THREADS)
56 Thread::Thread(int id) {
59 do_sleep = (id != 0); // Avoid a race with start_thinking()
60 is_searching = do_exit = false;
61 maxPly = splitPointsCnt = 0;
67 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
68 lock_init(splitPoints[j].lock);
70 if (!thread_create(handle, start_routine, this))
72 std::cerr << "Failed to create thread number " << id << std::endl;
82 do_exit = true; // Search must be already finished
85 thread_join(handle); // Wait for thread termination
87 lock_destroy(sleepLock);
88 cond_destroy(sleepCond);
90 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
91 lock_destroy(splitPoints[j].lock);
95 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
96 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
97 extern void check_time();
99 void Thread::timer_loop() {
103 lock_grab(sleepLock);
104 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
105 lock_release(sleepLock);
111 // Thread::main_loop() is where the main thread is parked waiting to be started
112 // when there is a new search. Main thread will launch all the slave threads.
114 void Thread::main_loop() {
118 lock_grab(sleepLock);
120 do_sleep = true; // Always return to sleep after a search
121 is_searching = false;
123 while (do_sleep && !do_exit)
125 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
126 cond_wait(sleepCond, sleepLock);
129 lock_release(sleepLock);
141 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
142 // or, if "sleeping threads" is used, when there is some work to do.
144 void Thread::wake_up() {
146 lock_grab(sleepLock);
147 cond_signal(sleepCond);
148 lock_release(sleepLock);
152 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
153 // reached while the program is pondering. The point is to work around a wrinkle
154 // in the UCI protocol: When pondering, the engine is not allowed to give a
155 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
156 // wait here until one of these commands (that raise StopRequest) is sent and
157 // then return, after which the bestmove and pondermove will be printed.
159 void Thread::wait_for_stop_or_ponderhit() {
161 Signals.stopOnPonderhit = true;
163 lock_grab(sleepLock);
165 while (!Signals.stop)
166 cond_wait(sleepCond, sleepLock);
168 lock_release(sleepLock);
172 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
173 // active split point, or in some ancestor of the split point.
175 bool Thread::cutoff_occurred() const {
177 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
185 // is_available_to() checks whether the thread is available to help the thread with
186 // threadID "master" at a split point. An obvious requirement is that thread must be
187 // idle. With more than two threads, this is not by itself sufficient: If the thread
188 // is the master of some active split point, it is only available as a slave to the
189 // threads which are busy searching the split point at the top of "slave"'s split
190 // point stack (the "helpful master concept" in YBWC terminology).
192 bool Thread::is_available_to(int master) const {
197 // Make a local copy to be sure doesn't become zero under our feet while
198 // testing next condition and so leading to an out of bound access.
199 int spCnt = splitPointsCnt;
201 // No active split points means that the thread is available as a slave for any
202 // other thread otherwise apply the "helpful master" concept if possible.
203 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master));
207 // read_uci_options() updates internal threads parameters from the corresponding
208 // UCI options. It is called before to start a new search.
210 void ThreadsManager::read_uci_options() {
212 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
213 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
214 useSleepingThreads = Options["Use Sleeping Threads"];
215 activeThreads = Options["Threads"];
217 // Dynamically allocate Thread object according to the number of
218 // active threads. This avoids preallocating memory for all possible
219 // threads if only few are used.
220 for (int i = 0; i < MAX_THREADS; i++)
221 if (i < activeThreads && !threads[i])
222 threads[i] = new Thread(i);
223 else if (i >= activeThreads && threads[i])
231 void ThreadsManager::wake_up() {
233 for (int i = 0; i < activeThreads; i++)
235 threads[i]->do_sleep = false;
236 threads[i]->wake_up();
241 void ThreadsManager::sleep() {
243 for (int i = 0; i < activeThreads; i++)
244 threads[i]->do_sleep = true;
248 // init() is called during startup. Initializes locks and condition variables
249 // and launches all threads sending them immediately to sleep.
251 void ThreadsManager::init() {
253 cond_init(sleepCond);
254 lock_init(splitLock);
255 timer = new Thread(MAX_THREADS);
256 read_uci_options(); // Creates at least main thread
260 // exit() is called to cleanly terminate the threads when the program finishes
262 void ThreadsManager::exit() {
264 for (int i = 0; i < MAX_THREADS; i++)
269 lock_destroy(splitLock);
270 cond_destroy(sleepCond);
274 // available_slave_exists() tries to find an idle thread which is available as
275 // a slave for the thread with threadID 'master'.
277 bool ThreadsManager::available_slave_exists(int master) const {
279 assert(master >= 0 && master < activeThreads);
281 for (int i = 0; i < activeThreads; i++)
282 if (threads[i]->is_available_to(master))
289 // split() does the actual work of distributing the work at a node between
290 // several available threads. If it does not succeed in splitting the node
291 // (because no idle threads are available, or because we have no unused split
292 // point objects), the function immediately returns. If splitting is possible, a
293 // SplitPoint object is initialized with all the data that must be copied to the
294 // helper threads and then helper threads are told that they have been assigned
295 // work. This will cause them to instantly leave their idle loops and call
296 // search(). When all threads have returned from search() then split() returns.
299 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
300 Value bestValue, Move* bestMove, Depth depth,
301 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
302 assert(pos.pos_is_ok());
303 assert(bestValue > -VALUE_INFINITE);
304 assert(bestValue <= alpha);
305 assert(alpha < beta);
306 assert(beta <= VALUE_INFINITE);
307 assert(depth > DEPTH_ZERO);
308 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
309 assert(activeThreads > 1);
311 int master = pos.thread();
312 Thread& masterThread = *threads[master];
314 if (masterThread.splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
317 // Pick the next available split point from the split point stack
318 SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt++];
320 sp->parent = masterThread.curSplitPoint;
323 sp->slavesMask = 1ULL << master;
325 sp->bestMove = *bestMove;
326 sp->threatMove = threatMove;
329 sp->nodeType = nodeType;
330 sp->bestValue = bestValue;
332 sp->moveCount = moveCount;
337 assert(masterThread.is_searching);
339 masterThread.curSplitPoint = sp;
342 // Try to allocate available threads and ask them to start searching setting
343 // is_searching flag. This must be done under lock protection to avoid concurrent
344 // allocation of the same slave by another master.
346 lock_grab(splitLock);
348 for (int i = 0; i < activeThreads && !Fake; i++)
349 if (threads[i]->is_available_to(master))
351 sp->slavesMask |= 1ULL << i;
352 threads[i]->curSplitPoint = sp;
353 threads[i]->is_searching = true; // Slave leaves idle_loop()
355 if (useSleepingThreads)
356 threads[i]->wake_up();
358 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
362 lock_release(splitLock);
363 lock_release(sp->lock);
365 // Everything is set up. The master thread enters the idle loop, from which
366 // it will instantly launch a search, because its is_searching flag is set.
367 // We pass the split point as a parameter to the idle loop, which means that
368 // the thread will return from the idle loop when all slaves have finished
369 // their work at this split point.
370 if (slavesCnt || Fake)
372 masterThread.idle_loop(sp);
374 // In helpful master concept a master can help only a sub-tree of its split
375 // point, and because here is all finished is not possible master is booked.
376 assert(!masterThread.is_searching);
379 // We have returned from the idle loop, which means that all threads are
380 // finished. Note that setting is_searching and decreasing splitPointsCnt is
381 // done under lock protection to avoid a race with Thread::is_available_to().
382 lock_grab(sp->lock); // To protect sp->nodes
383 lock_grab(splitLock);
385 masterThread.is_searching = true;
386 masterThread.splitPointsCnt--;
387 masterThread.curSplitPoint = sp->parent;
388 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
389 *bestMove = sp->bestMove;
391 lock_release(splitLock);
392 lock_release(sp->lock);
394 return sp->bestValue;
397 // Explicit template instantiations
398 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
399 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
402 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
403 // milliseconds. If msec is 0 then timer is stopped.
405 void ThreadsManager::set_timer(int msec) {
407 lock_grab(timer->sleepLock);
408 timer->maxPly = msec;
409 cond_signal(timer->sleepCond); // Wake up and restart the timer
410 lock_release(timer->sleepLock);
414 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
415 // thread parked in main_loop() and starting a new search. If asyncMode is true
416 // then function returns immediately, otherwise caller is blocked waiting for
417 // the search to finish.
419 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
420 const std::set<Move>& searchMoves, bool async) {
421 Thread& main = *threads[0];
423 lock_grab(main.sleepLock);
425 // Wait main thread has finished before to launch a new search
426 while (!main.do_sleep)
427 cond_wait(sleepCond, main.sleepLock);
429 // Copy input arguments to initialize the search
430 RootPosition.copy(pos, 0);
434 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
435 // set is given, with the subset of legal moves to search.
436 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
437 if (searchMoves.empty() || searchMoves.count(ml.move()))
438 RootMoves.push_back(RootMove(ml.move()));
440 // Reset signals before to start the new search
441 Signals.stopOnPonderhit = Signals.firstRootMove = false;
442 Signals.stop = Signals.failedLowAtRoot = false;
444 main.do_sleep = false;
445 cond_signal(main.sleepCond); // Wake up main thread and start searching
448 while (!main.do_sleep)
449 cond_wait(sleepCond, main.sleepLock);
451 lock_release(main.sleepLock);
455 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
456 // and to wait for the main thread finishing the search. Needed to wait exiting
457 // and terminate the threads after a 'quit' command.
459 void ThreadsManager::stop_thinking() {
461 Thread& main = *threads[0];
463 Search::Signals.stop = true;
465 lock_grab(main.sleepLock);
467 cond_signal(main.sleepCond); // In case is waiting for stop or ponderhit
469 while (!main.do_sleep)
470 cond_wait(sleepCond, main.sleepLock);
472 lock_release(main.sleepLock);