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().
40 DWORD WINAPI start_routine(LPVOID thread) {
42 void* start_routine(void* thread) {
45 Thread* th = (Thread*)thread;
47 if (th->threadID == 0)
50 else if (th->threadID == MAX_THREADS)
62 // wake_up() wakes up the thread, normally at the beginning of the search or,
63 // if "sleeping threads" is used, when there is some work to do.
65 void Thread::wake_up() {
67 lock_grab(&sleepLock);
68 cond_signal(&sleepCond);
69 lock_release(&sleepLock);
73 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
74 // active split point, or in some ancestor of the split point.
76 bool Thread::cutoff_occurred() const {
78 for (SplitPoint* sp = splitPoint; sp; sp = sp->parent)
79 if (sp->is_betaCutoff)
86 // is_available_to() checks whether the thread is available to help the thread with
87 // threadID "master" at a split point. An obvious requirement is that thread must be
88 // idle. With more than two threads, this is not by itself sufficient: If the thread
89 // is the master of some active split point, it is only available as a slave to the
90 // threads which are busy searching the split point at the top of "slave"'s split
91 // point stack (the "helpful master concept" in YBWC terminology).
93 bool Thread::is_available_to(int master) const {
98 // Make a local copy to be sure doesn't become zero under our feet while
99 // testing next condition and so leading to an out of bound access.
100 int localActiveSplitPoints = activeSplitPoints;
102 // No active split points means that the thread is available as a slave for any
103 // other thread otherwise apply the "helpful master" concept if possible.
104 if ( !localActiveSplitPoints
105 || splitPoints[localActiveSplitPoints - 1].is_slave[master])
112 // read_uci_options() updates number of active threads and other parameters
113 // according to the UCI options values. It is called before to start a new search.
115 void ThreadsManager::read_uci_options() {
117 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
118 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
119 useSleepingThreads = Options["Use Sleeping Threads"];
121 set_size(Options["Threads"]);
125 // set_size() changes the number of active threads and raises do_sleep flag for
126 // all the unused threads that will go immediately to sleep.
128 void ThreadsManager::set_size(int cnt) {
130 assert(cnt > 0 && cnt <= MAX_THREADS);
134 for (int i = 1; i < MAX_THREADS; i++) // Ignore main thread
135 if (i < activeThreads)
137 // Dynamically allocate pawn and material hash tables according to the
138 // number of active threads. This avoids preallocating memory for all
139 // possible threads if only few are used.
140 threads[i].pawnTable.init();
141 threads[i].materialTable.init();
143 threads[i].do_sleep = false;
146 threads[i].do_sleep = true;
150 // init() is called during startup. Initializes locks and condition variables
151 // and launches all threads sending them immediately to sleep.
153 void ThreadsManager::init() {
155 // Initialize sleep condition and lock used by thread manager
156 cond_init(&sleepCond);
157 lock_init(&threadsLock);
159 // Initialize thread's sleep conditions and split point locks
160 for (int i = 0; i <= MAX_THREADS; i++)
162 lock_init(&threads[i].sleepLock);
163 cond_init(&threads[i].sleepCond);
165 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
166 lock_init(&(threads[i].splitPoints[j].lock));
169 // Allocate main thread tables to call evaluate() also when not searching
170 threads[0].pawnTable.init();
171 threads[0].materialTable.init();
173 // Create and launch all the threads, threads will go immediately to sleep
174 for (int i = 0; i <= MAX_THREADS; i++)
176 threads[i].is_searching = false;
177 threads[i].do_sleep = (i != 0); // Avoid a race with start_thinking()
178 threads[i].threadID = i;
180 #if defined(_MSC_VER)
181 threads[i].handle = CreateThread(NULL, 0, start_routine, &threads[i], 0, NULL);
182 bool ok = (threads[i].handle != NULL);
184 bool ok = !pthread_create(&threads[i].handle, NULL, start_routine, &threads[i]);
189 std::cerr << "Failed to create thread number " << i << std::endl;
190 ::exit(EXIT_FAILURE);
196 // exit() is called to cleanly terminate the threads when the program finishes
198 void ThreadsManager::exit() {
200 for (int i = 0; i <= MAX_THREADS; i++)
202 threads[i].do_terminate = true; // Search must be already finished
203 threads[i].wake_up();
205 // Wait for thread termination
206 #if defined(_MSC_VER)
207 WaitForSingleObject(threads[i].handle, INFINITE);
208 CloseHandle(threads[i].handle);
210 pthread_join(threads[i].handle, NULL);
213 // Now we can safely destroy associated locks and wait conditions
214 lock_destroy(&threads[i].sleepLock);
215 cond_destroy(&threads[i].sleepCond);
217 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
218 lock_destroy(&(threads[i].splitPoints[j].lock));
221 lock_destroy(&threadsLock);
222 cond_destroy(&sleepCond);
226 // available_slave_exists() tries to find an idle thread which is available as
227 // a slave for the thread with threadID 'master'.
229 bool ThreadsManager::available_slave_exists(int master) const {
231 assert(master >= 0 && master < activeThreads);
233 for (int i = 0; i < activeThreads; i++)
234 if (threads[i].is_available_to(master))
241 // split_point_finished() checks if all the slave threads of a given split
242 // point have finished searching.
244 bool ThreadsManager::split_point_finished(SplitPoint* sp) const {
246 for (int i = 0; i < activeThreads; i++)
254 // split() does the actual work of distributing the work at a node between
255 // several available threads. If it does not succeed in splitting the node
256 // (because no idle threads are available, or because we have no unused split
257 // point objects), the function immediately returns. If splitting is possible, a
258 // SplitPoint object is initialized with all the data that must be copied to the
259 // helper threads and then helper threads are told that they have been assigned
260 // work. This will cause them to instantly leave their idle loops and call
261 // search(). When all threads have returned from search() then split() returns.
264 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
265 Value bestValue, Depth depth, Move threatMove,
266 int moveCount, MovePicker* mp, int nodeType) {
267 assert(pos.pos_is_ok());
268 assert(bestValue > -VALUE_INFINITE);
269 assert(bestValue <= alpha);
270 assert(alpha < beta);
271 assert(beta <= VALUE_INFINITE);
272 assert(depth > DEPTH_ZERO);
273 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
274 assert(activeThreads > 1);
276 int i, master = pos.thread();
277 Thread& masterThread = threads[master];
279 // If we already have too many active split points, don't split
280 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
283 // Pick the next available split point from the split point stack
284 SplitPoint* sp = &masterThread.splitPoints[masterThread.activeSplitPoints];
286 // Initialize the split point
287 sp->parent = masterThread.splitPoint;
289 sp->is_betaCutoff = false;
291 sp->threatMove = threatMove;
294 sp->nodeType = nodeType;
295 sp->bestValue = bestValue;
297 sp->moveCount = moveCount;
302 for (i = 0; i < activeThreads; i++)
303 sp->is_slave[i] = false;
305 // If we are here it means we are not available
306 assert(masterThread.is_searching);
308 int workersCnt = 1; // At least the master is included
310 // Try to allocate available threads and ask them to start searching setting
311 // is_searching flag. This must be done under lock protection to avoid concurrent
312 // allocation of the same slave by another master.
313 lock_grab(&threadsLock);
315 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
316 if (threads[i].is_available_to(master))
319 sp->is_slave[i] = true;
320 threads[i].splitPoint = sp;
322 // This makes the slave to exit from idle_loop()
323 threads[i].is_searching = true;
325 if (useSleepingThreads)
326 threads[i].wake_up();
329 lock_release(&threadsLock);
331 // We failed to allocate even one slave, return
332 if (!Fake && workersCnt == 1)
335 masterThread.splitPoint = sp;
336 masterThread.activeSplitPoints++;
338 // Everything is set up. The master thread enters the idle loop, from which
339 // it will instantly launch a search, because its is_searching flag is set.
340 // We pass the split point as a parameter to the idle loop, which means that
341 // the thread will return from the idle loop when all slaves have finished
342 // their work at this split point.
343 masterThread.idle_loop(sp);
345 // In helpful master concept a master can help only a sub-tree of its split
346 // point, and because here is all finished is not possible master is booked.
347 assert(!masterThread.is_searching);
349 // We have returned from the idle loop, which means that all threads are
350 // finished. Note that changing state and decreasing activeSplitPoints is done
351 // under lock protection to avoid a race with Thread::is_available_to().
352 lock_grab(&threadsLock);
354 masterThread.is_searching = true;
355 masterThread.activeSplitPoints--;
357 lock_release(&threadsLock);
359 masterThread.splitPoint = sp->parent;
360 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
362 return sp->bestValue;
365 // Explicit template instantiations
366 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
367 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
370 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
371 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
372 extern void check_time();
374 void Thread::timer_loop() {
376 while (!do_terminate)
378 lock_grab(&sleepLock);
379 timed_wait(&sleepCond, &sleepLock, maxPly ? maxPly : INT_MAX);
380 lock_release(&sleepLock);
386 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
387 // milliseconds. If msec is 0 then timer is stopped.
389 void ThreadsManager::set_timer(int msec) {
391 Thread& timer = threads[MAX_THREADS];
393 lock_grab(&timer.sleepLock);
395 cond_signal(&timer.sleepCond); // Wake up and restart the timer
396 lock_release(&timer.sleepLock);
400 // Thread::main_loop() is where the main thread is parked waiting to be started
401 // when there is a new search. Main thread will launch all the slave threads.
403 void Thread::main_loop() {
407 lock_grab(&sleepLock);
409 do_sleep = true; // Always return to sleep after a search
410 is_searching = false;
412 while (do_sleep && !do_terminate)
414 cond_signal(&Threads.sleepCond); // Wake up UI thread if needed
415 cond_wait(&sleepCond, &sleepLock);
420 lock_release(&sleepLock);
430 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
431 // thread parked in main_loop() and starting a new search. If asyncMode is true
432 // then function returns immediately, otherwise caller is blocked waiting for
433 // the search to finish.
435 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
436 const std::set<Move>& searchMoves, bool async) {
437 Thread& main = threads[0];
439 lock_grab(&main.sleepLock);
441 // Wait main thread has finished before to launch a new search
442 while (!main.do_sleep)
443 cond_wait(&sleepCond, &main.sleepLock);
445 // Copy input arguments to initialize the search
446 RootPosition.copy(pos, 0);
450 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
451 // set is given, with the subset of legal moves to search.
452 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
453 if (searchMoves.empty() || searchMoves.count(ml.move()))
454 RootMoves.push_back(RootMove(ml.move()));
456 // Reset signals before to start the new search
457 Signals.stopOnPonderhit = Signals.firstRootMove = false;
458 Signals.stop = Signals.failedLowAtRoot = false;
460 main.do_sleep = false;
461 cond_signal(&main.sleepCond); // Wake up main thread and start searching
464 while (!main.do_sleep)
465 cond_wait(&sleepCond, &main.sleepLock);
467 lock_release(&main.sleepLock);
471 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
472 // and to wait for the main thread finishing the search. Needed to wait exiting
473 // and terminate the threads after a 'quit' command.
475 void ThreadsManager::stop_thinking() {
477 Thread& main = threads[0];
479 Search::Signals.stop = true;
481 lock_grab(&main.sleepLock);
483 cond_signal(&main.sleepCond); // In case is waiting for stop or ponderhit
485 while (!main.do_sleep)
486 cond_wait(&sleepCond, &main.sleepLock);
488 lock_release(&main.sleepLock);
492 // ThreadsManager::wait_for_stop_or_ponderhit() is called when the maximum depth
493 // is reached while the program is pondering. The point is to work around a wrinkle
494 // in the UCI protocol: When pondering, the engine is not allowed to give a
495 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
496 // wait here until one of these commands (that raise StopRequest) is sent and
497 // then return, after which the bestmove and pondermove will be printed.
499 void ThreadsManager::wait_for_stop_or_ponderhit() {
501 Signals.stopOnPonderhit = true;
503 Thread& main = threads[0];
505 lock_grab(&main.sleepLock);
507 while (!Signals.stop)
508 cond_wait(&main.sleepCond, &main.sleepLock);
510 lock_release(&main.sleepLock);