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 c'tor creates and launches the OS thread, that will go immediately to
59 Thread::Thread(int id) {
61 is_searching = do_exit = false;
62 maxPly = splitPointsCnt = 0;
65 do_sleep = (id != 0); // Avoid a race with start_thinking()
70 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
71 lock_init(splitPoints[j].lock);
73 if (!thread_create(handle, start_routine, this))
75 std::cerr << "Failed to create thread number " << id << std::endl;
81 // Thread d'tor will wait for thread termination before to return.
87 do_exit = true; // Search must be already finished
90 thread_join(handle); // Wait for thread termination
92 lock_destroy(sleepLock);
93 cond_destroy(sleepCond);
95 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
96 lock_destroy(splitPoints[j].lock);
100 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
101 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
102 extern void check_time();
104 void Thread::timer_loop() {
108 lock_grab(sleepLock);
109 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
110 lock_release(sleepLock);
116 // Thread::main_loop() is where the main thread is parked waiting to be started
117 // when there is a new search. Main thread will launch all the slave threads.
119 void Thread::main_loop() {
123 lock_grab(sleepLock);
125 do_sleep = true; // Always return to sleep after a search
126 is_searching = false;
128 while (do_sleep && !do_exit)
130 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
131 cond_wait(sleepCond, sleepLock);
134 lock_release(sleepLock);
146 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
147 // or, if "sleeping threads" is used, when there is some work to do.
149 void Thread::wake_up() {
151 lock_grab(sleepLock);
152 cond_signal(sleepCond);
153 lock_release(sleepLock);
157 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
158 // reached while the program is pondering. The point is to work around a wrinkle
159 // in the UCI protocol: When pondering, the engine is not allowed to give a
160 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
161 // wait here until one of these commands (that raise StopRequest) is sent and
162 // then return, after which the bestmove and pondermove will be printed.
164 void Thread::wait_for_stop_or_ponderhit() {
166 Signals.stopOnPonderhit = true;
168 lock_grab(sleepLock);
170 while (!Signals.stop)
171 cond_wait(sleepCond, sleepLock);
173 lock_release(sleepLock);
177 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
178 // active split point, or in some ancestor of the split point.
180 bool Thread::cutoff_occurred() const {
182 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
190 // is_available_to() checks whether the thread is available to help the thread with
191 // threadID "master" at a split point. An obvious requirement is that thread must be
192 // idle. With more than two threads, this is not by itself sufficient: If the thread
193 // is the master of some active split point, it is only available as a slave to the
194 // threads which are busy searching the split point at the top of "slave"'s split
195 // point stack (the "helpful master concept" in YBWC terminology).
197 bool Thread::is_available_to(int master) const {
202 // Make a local copy to be sure doesn't become zero under our feet while
203 // testing next condition and so leading to an out of bound access.
204 int spCnt = splitPointsCnt;
206 // No active split points means that the thread is available as a slave for any
207 // other thread otherwise apply the "helpful master" concept if possible.
208 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master));
212 // read_uci_options() updates internal threads parameters from the corresponding
213 // UCI options and creates/destroys threads to match the requested number. Thread
214 // objects are dynamically allocated to avoid creating in advance all possible
215 // threads, with included pawns and material tables, if only few are used.
217 void ThreadsManager::read_uci_options() {
219 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
220 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
221 useSleepingThreads = Options["Use Sleeping Threads"];
222 int requested = Options["Threads"];
224 while (size() < requested)
225 threads.push_back(new Thread(size()));
227 while (size() > requested)
229 delete threads.back();
235 // wake_up() is called before a new search to start the threads that are waiting
236 // on the sleep condition. If useSleepingThreads is set threads will be woken up
239 void ThreadsManager::wake_up() {
241 for (int i = 0; i < size(); i++)
243 threads[i]->do_sleep = false;
245 if (!useSleepingThreads)
246 threads[i]->wake_up();
251 // sleep() is called after the search to ask threads to wait on sleep condition
253 void ThreadsManager::sleep() {
255 for (int i = 0; i < size(); i++)
256 threads[i]->do_sleep = true;
260 // init() is called during startup. Initializes locks and condition variables
261 // and launches all threads sending them immediately to sleep.
263 void ThreadsManager::init() {
265 cond_init(sleepCond);
266 lock_init(splitLock);
267 timer = new Thread(MAX_THREADS);
268 read_uci_options(); // Creates at least the main thread
272 // exit() is called to cleanly terminate the threads before the program finishes
274 void ThreadsManager::exit() {
276 for (int i = 0; i < size(); i++)
280 lock_destroy(splitLock);
281 cond_destroy(sleepCond);
285 // available_slave_exists() tries to find an idle thread which is available as
286 // a slave for the thread with threadID 'master'.
288 bool ThreadsManager::available_slave_exists(int master) const {
290 assert(master >= 0 && master < size());
292 for (int i = 0; i < size(); i++)
293 if (threads[i]->is_available_to(master))
300 // split() does the actual work of distributing the work at a node between
301 // several available threads. If it does not succeed in splitting the node
302 // (because no idle threads are available, or because we have no unused split
303 // point objects), the function immediately returns. If splitting is possible, a
304 // SplitPoint object is initialized with all the data that must be copied to the
305 // helper threads and then helper threads are told that they have been assigned
306 // work. This will cause them to instantly leave their idle loops and call
307 // search(). When all threads have returned from search() then split() returns.
310 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
311 Value bestValue, Move* bestMove, Depth depth,
312 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
313 assert(pos.pos_is_ok());
314 assert(bestValue > -VALUE_INFINITE);
315 assert(bestValue <= alpha);
316 assert(alpha < beta);
317 assert(beta <= VALUE_INFINITE);
318 assert(depth > DEPTH_ZERO);
320 int master = pos.thread();
321 Thread& masterThread = *threads[master];
323 if (masterThread.splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
326 // Pick the next available split point from the split point stack
327 SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt++];
329 sp->parent = masterThread.curSplitPoint;
332 sp->slavesMask = 1ULL << master;
334 sp->bestMove = *bestMove;
335 sp->threatMove = threatMove;
338 sp->nodeType = nodeType;
339 sp->bestValue = bestValue;
341 sp->moveCount = moveCount;
346 assert(masterThread.is_searching);
348 masterThread.curSplitPoint = sp;
351 // Try to allocate available threads and ask them to start searching setting
352 // is_searching flag. This must be done under lock protection to avoid concurrent
353 // allocation of the same slave by another master.
355 lock_grab(splitLock);
357 for (int i = 0; i < size() && !Fake; ++i)
358 if (threads[i]->is_available_to(master))
360 sp->slavesMask |= 1ULL << i;
361 threads[i]->curSplitPoint = sp;
362 threads[i]->is_searching = true; // Slave leaves idle_loop()
364 if (useSleepingThreads)
365 threads[i]->wake_up();
367 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
371 lock_release(splitLock);
372 lock_release(sp->lock);
374 // Everything is set up. The master thread enters the idle loop, from which
375 // it will instantly launch a search, because its is_searching flag is set.
376 // We pass the split point as a parameter to the idle loop, which means that
377 // the thread will return from the idle loop when all slaves have finished
378 // their work at this split point.
379 if (slavesCnt || Fake)
381 masterThread.idle_loop(sp);
383 // In helpful master concept a master can help only a sub-tree of its split
384 // point, and because here is all finished is not possible master is booked.
385 assert(!masterThread.is_searching);
388 // We have returned from the idle loop, which means that all threads are
389 // finished. Note that setting is_searching and decreasing splitPointsCnt is
390 // done under lock protection to avoid a race with Thread::is_available_to().
391 lock_grab(sp->lock); // To protect sp->nodes
392 lock_grab(splitLock);
394 masterThread.is_searching = true;
395 masterThread.splitPointsCnt--;
396 masterThread.curSplitPoint = sp->parent;
397 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
398 *bestMove = sp->bestMove;
400 lock_release(splitLock);
401 lock_release(sp->lock);
403 return sp->bestValue;
406 // Explicit template instantiations
407 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
408 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
411 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
412 // milliseconds. If msec is 0 then timer is stopped.
414 void ThreadsManager::set_timer(int msec) {
416 lock_grab(timer->sleepLock);
417 timer->maxPly = msec;
418 cond_signal(timer->sleepCond); // Wake up and restart the timer
419 lock_release(timer->sleepLock);
423 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
424 // thread parked in main_loop() and starting a new search. If asyncMode is true
425 // then function returns immediately, otherwise caller is blocked waiting for
426 // the search to finish.
428 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
429 const std::set<Move>& searchMoves, bool async) {
430 Thread& main = *threads.front();
432 lock_grab(main.sleepLock);
434 // Wait main thread has finished before to launch a new search
435 while (!main.do_sleep)
436 cond_wait(sleepCond, main.sleepLock);
438 // Copy input arguments to initialize the search
439 RootPosition.copy(pos, 0);
443 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
444 // set is given, with the subset of legal moves to search.
445 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
446 if (searchMoves.empty() || searchMoves.count(ml.move()))
447 RootMoves.push_back(RootMove(ml.move()));
449 // Reset signals before to start the new search
450 Signals.stopOnPonderhit = Signals.firstRootMove = false;
451 Signals.stop = Signals.failedLowAtRoot = false;
453 main.do_sleep = false;
454 cond_signal(main.sleepCond); // Wake up main thread and start searching
457 while (!main.do_sleep)
458 cond_wait(sleepCond, main.sleepLock);
460 lock_release(main.sleepLock);
464 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
465 // and to wait for the main thread finishing the search. Needed to wait exiting
466 // and terminate the threads after a 'quit' command.
468 void ThreadsManager::stop_thinking() {
470 Thread& main = *threads.front();
472 Search::Signals.stop = true;
474 lock_grab(main.sleepLock);
476 cond_signal(main.sleepCond); // In case is waiting for stop or ponderhit
478 while (!main.do_sleep)
479 cond_wait(sleepCond, main.sleepLock);
481 lock_release(main.sleepLock);