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::timer_loop() is where the timer thread waits maxPly milliseconds and
57 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
58 extern void check_time();
60 void Thread::timer_loop() {
65 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
66 lock_release(sleepLock);
72 // Thread::main_loop() is where the main thread is parked waiting to be started
73 // when there is a new search. Main thread will launch all the slave threads.
75 void Thread::main_loop() {
81 do_sleep = true; // Always return to sleep after a search
84 while (do_sleep && !do_exit)
86 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
87 cond_wait(sleepCond, sleepLock);
90 lock_release(sleepLock);
102 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
103 // or, if "sleeping threads" is used, when there is some work to do.
105 void Thread::wake_up() {
107 lock_grab(sleepLock);
108 cond_signal(sleepCond);
109 lock_release(sleepLock);
113 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
114 // reached while the program is pondering. The point is to work around a wrinkle
115 // in the UCI protocol: When pondering, the engine is not allowed to give a
116 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
117 // wait here until one of these commands (that raise StopRequest) is sent and
118 // then return, after which the bestmove and pondermove will be printed.
120 void Thread::wait_for_stop_or_ponderhit() {
122 Signals.stopOnPonderhit = true;
124 lock_grab(sleepLock);
126 while (!Signals.stop)
127 cond_wait(sleepCond, sleepLock);
129 lock_release(sleepLock);
133 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
134 // active split point, or in some ancestor of the split point.
136 bool Thread::cutoff_occurred() const {
138 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
146 // is_available_to() checks whether the thread is available to help the thread with
147 // threadID "master" at a split point. An obvious requirement is that thread must be
148 // idle. With more than two threads, this is not by itself sufficient: If the thread
149 // is the master of some active split point, it is only available as a slave to the
150 // threads which are busy searching the split point at the top of "slave"'s split
151 // point stack (the "helpful master concept" in YBWC terminology).
153 bool Thread::is_available_to(int master) const {
158 // Make a local copy to be sure doesn't become zero under our feet while
159 // testing next condition and so leading to an out of bound access.
160 int spCnt = splitPointsCnt;
162 // No active split points means that the thread is available as a slave for any
163 // other thread otherwise apply the "helpful master" concept if possible.
164 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master));
168 // read_uci_options() updates internal threads parameters from the corresponding
169 // UCI options. It is called before to start a new search.
171 void ThreadsManager::read_uci_options() {
173 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
174 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
175 useSleepingThreads = Options["Use Sleeping Threads"];
176 activeThreads = Options["Threads"];
178 // Dynamically allocate pawn and material hash tables according to the
179 // number of active threads. This avoids preallocating memory for all
180 // possible threads if only few are used.
181 for (int i = 0; i < MAX_THREADS; i++)
182 if (i < activeThreads)
184 threads[i].pawnTable.init();
185 threads[i].materialTable.init();
186 threads[i].maxPly = 0;
191 void ThreadsManager::wake_up() {
193 for (int i = 0; i < activeThreads; i++)
195 threads[i].do_sleep = false;
196 threads[i].wake_up();
201 void ThreadsManager::sleep() {
203 for (int i = 0; i < activeThreads; i++)
204 threads[i].do_sleep = true;
208 // init() is called during startup. Initializes locks and condition variables
209 // and launches all threads sending them immediately to sleep.
211 void ThreadsManager::init() {
215 cond_init(sleepCond);
216 lock_init(splitLock);
218 // Allocate main thread tables to call evaluate() also when not searching
219 threads[0].pawnTable.init();
220 threads[0].materialTable.init();
222 // Create and launch all the threads, threads will go immediately to sleep
223 for (int i = 0; i <= MAX_THREADS; i++)
225 threads[i].is_searching = false;
226 threads[i].do_sleep = (i != 0); // Avoid a race with start_thinking()
227 threads[i].threadID = i;
229 lock_init(threads[i].sleepLock);
230 cond_init(threads[i].sleepCond);
232 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
233 lock_init(threads[i].splitPoints[j].lock);
235 if (!thread_create(threads[i].handle, start_routine, threads[i]))
237 std::cerr << "Failed to create thread number " << i << std::endl;
238 ::exit(EXIT_FAILURE);
244 // exit() is called to cleanly terminate the threads when the program finishes
246 void ThreadsManager::exit() {
248 for (int i = 0; i <= MAX_THREADS; i++)
250 assert(threads[i].do_sleep);
252 threads[i].do_exit = true; // Search must be already finished
253 threads[i].wake_up();
255 thread_join(threads[i].handle); // Wait for thread termination
257 lock_destroy(threads[i].sleepLock);
258 cond_destroy(threads[i].sleepCond);
260 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
261 lock_destroy(threads[i].splitPoints[j].lock);
264 lock_destroy(splitLock);
265 cond_destroy(sleepCond);
269 // available_slave_exists() tries to find an idle thread which is available as
270 // a slave for the thread with threadID 'master'.
272 bool ThreadsManager::available_slave_exists(int master) const {
274 assert(master >= 0 && master < activeThreads);
276 for (int i = 0; i < activeThreads; i++)
277 if (threads[i].is_available_to(master))
284 // split() does the actual work of distributing the work at a node between
285 // several available threads. If it does not succeed in splitting the node
286 // (because no idle threads are available, or because we have no unused split
287 // point objects), the function immediately returns. If splitting is possible, a
288 // SplitPoint object is initialized with all the data that must be copied to the
289 // helper threads and then helper threads are told that they have been assigned
290 // work. This will cause them to instantly leave their idle loops and call
291 // search(). When all threads have returned from search() then split() returns.
294 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
295 Value bestValue, Move* bestMove, Depth depth,
296 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
297 assert(pos.pos_is_ok());
298 assert(bestValue > -VALUE_INFINITE);
299 assert(bestValue <= alpha);
300 assert(alpha < beta);
301 assert(beta <= VALUE_INFINITE);
302 assert(depth > DEPTH_ZERO);
303 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
304 assert(activeThreads > 1);
306 int master = pos.thread();
307 Thread& masterThread = threads[master];
309 if (masterThread.splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
312 // Pick the next available split point from the split point stack
313 SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt++];
315 sp->parent = masterThread.curSplitPoint;
318 sp->slavesMask = 1ULL << master;
320 sp->bestMove = *bestMove;
321 sp->threatMove = threatMove;
324 sp->nodeType = nodeType;
325 sp->bestValue = bestValue;
327 sp->moveCount = moveCount;
332 assert(masterThread.is_searching);
334 masterThread.curSplitPoint = sp;
337 // Try to allocate available threads and ask them to start searching setting
338 // is_searching flag. This must be done under lock protection to avoid concurrent
339 // allocation of the same slave by another master.
341 lock_grab(splitLock);
343 for (int i = 0; i < activeThreads && !Fake; i++)
344 if (threads[i].is_available_to(master))
346 sp->slavesMask |= 1ULL << i;
347 threads[i].curSplitPoint = sp;
348 threads[i].is_searching = true; // Slave leaves idle_loop()
350 if (useSleepingThreads)
351 threads[i].wake_up();
353 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
357 lock_release(splitLock);
358 lock_release(sp->lock);
360 // Everything is set up. The master thread enters the idle loop, from which
361 // it will instantly launch a search, because its is_searching flag is set.
362 // We pass the split point as a parameter to the idle loop, which means that
363 // the thread will return from the idle loop when all slaves have finished
364 // their work at this split point.
365 if (slavesCnt || Fake)
367 masterThread.idle_loop(sp);
369 // In helpful master concept a master can help only a sub-tree of its split
370 // point, and because here is all finished is not possible master is booked.
371 assert(!masterThread.is_searching);
374 // We have returned from the idle loop, which means that all threads are
375 // finished. Note that setting is_searching and decreasing splitPointsCnt is
376 // done under lock protection to avoid a race with Thread::is_available_to().
377 lock_grab(sp->lock); // To protect sp->nodes
378 lock_grab(splitLock);
380 masterThread.is_searching = true;
381 masterThread.splitPointsCnt--;
382 masterThread.curSplitPoint = sp->parent;
383 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
384 *bestMove = sp->bestMove;
386 lock_release(splitLock);
387 lock_release(sp->lock);
389 return sp->bestValue;
392 // Explicit template instantiations
393 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
394 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
397 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
398 // milliseconds. If msec is 0 then timer is stopped.
400 void ThreadsManager::set_timer(int msec) {
402 Thread& timer = threads[MAX_THREADS];
404 lock_grab(timer.sleepLock);
406 cond_signal(timer.sleepCond); // Wake up and restart the timer
407 lock_release(timer.sleepLock);
411 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
412 // thread parked in main_loop() and starting a new search. If asyncMode is true
413 // then function returns immediately, otherwise caller is blocked waiting for
414 // the search to finish.
416 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
417 const std::set<Move>& searchMoves, bool async) {
418 Thread& main = threads[0];
420 lock_grab(main.sleepLock);
422 // Wait main thread has finished before to launch a new search
423 while (!main.do_sleep)
424 cond_wait(sleepCond, main.sleepLock);
426 // Copy input arguments to initialize the search
427 RootPosition.copy(pos, 0);
431 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
432 // set is given, with the subset of legal moves to search.
433 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
434 if (searchMoves.empty() || searchMoves.count(ml.move()))
435 RootMoves.push_back(RootMove(ml.move()));
437 // Reset signals before to start the new search
438 Signals.stopOnPonderhit = Signals.firstRootMove = false;
439 Signals.stop = Signals.failedLowAtRoot = false;
441 main.do_sleep = false;
442 cond_signal(main.sleepCond); // Wake up main thread and start searching
445 while (!main.do_sleep)
446 cond_wait(sleepCond, main.sleepLock);
448 lock_release(main.sleepLock);
452 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
453 // and to wait for the main thread finishing the search. Needed to wait exiting
454 // and terminate the threads after a 'quit' command.
456 void ThreadsManager::stop_thinking() {
458 Thread& main = threads[0];
460 Search::Signals.stop = true;
462 lock_grab(main.sleepLock);
464 cond_signal(main.sleepCond); // In case is waiting for stop or ponderhit
466 while (!main.do_sleep)
467 cond_wait(sleepCond, main.sleepLock);
469 lock_release(main.sleepLock);