2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
24 #include "ucioption.h"
26 ThreadsManager Threads; // Global object
28 namespace { extern "C" {
30 // start_routine() is the C function which is called when a new thread
31 // is launched. It simply calls idle_loop() of the supplied thread. The first
32 // and last thread are special. First one is the main search thread while the
33 // last one mimics a timer, they run in main_loop() and timer_loop().
36 DWORD WINAPI start_routine(LPVOID thread) {
38 void* start_routine(void* thread) {
41 Thread* th = (Thread*)thread;
43 if (th->threadID == 0)
46 else if (th->threadID == MAX_THREADS)
58 // wake_up() wakes up the thread, normally at the beginning of the search or,
59 // if "sleeping threads" is used, when there is some work to do.
61 void Thread::wake_up() {
63 lock_grab(&sleepLock);
64 cond_signal(&sleepCond);
65 lock_release(&sleepLock);
69 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
70 // active split point, or in some ancestor of the split point.
72 bool Thread::cutoff_occurred() const {
74 for (SplitPoint* sp = splitPoint; sp; sp = sp->parent)
75 if (sp->is_betaCutoff)
82 // is_available_to() checks whether the thread is available to help the thread with
83 // threadID "master" at a split point. An obvious requirement is that thread must be
84 // idle. With more than two threads, this is not by itself sufficient: If the thread
85 // is the master of some active split point, it is only available as a slave to the
86 // threads which are busy searching the split point at the top of "slave"'s split
87 // point stack (the "helpful master concept" in YBWC terminology).
89 bool Thread::is_available_to(int master) const {
94 // Make a local copy to be sure doesn't become zero under our feet while
95 // testing next condition and so leading to an out of bound access.
96 int localActiveSplitPoints = activeSplitPoints;
98 // No active split points means that the thread is available as a slave for any
99 // other thread otherwise apply the "helpful master" concept if possible.
100 if ( !localActiveSplitPoints
101 || splitPoints[localActiveSplitPoints - 1].is_slave[master])
108 // read_uci_options() updates number of active threads and other parameters
109 // according to the UCI options values. It is called before to start a new search.
111 void ThreadsManager::read_uci_options() {
113 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
114 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
115 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
117 set_size(Options["Threads"].value<int>());
121 // set_size() changes the number of active threads and raises do_sleep flag for
122 // all the unused threads that will go immediately to sleep.
124 void ThreadsManager::set_size(int cnt) {
126 assert(cnt > 0 && cnt <= MAX_THREADS);
130 for (int i = 1; i < MAX_THREADS; i++) // Ignore main thread
131 if (i < activeThreads)
133 // Dynamically allocate pawn and material hash tables according to the
134 // number of active threads. This avoids preallocating memory for all
135 // possible threads if only few are used.
136 threads[i].pawnTable.init();
137 threads[i].materialTable.init();
139 threads[i].do_sleep = false;
142 threads[i].do_sleep = true;
146 // init() is called during startup. Initializes locks and condition variables
147 // and launches all threads sending them immediately to sleep.
149 void ThreadsManager::init() {
151 // Initialize sleep condition and lock used by thread manager
152 cond_init(&sleepCond);
153 lock_init(&threadsLock);
155 // Initialize thread's sleep conditions and split point locks
156 for (int i = 0; i <= MAX_THREADS; i++)
158 lock_init(&threads[i].sleepLock);
159 cond_init(&threads[i].sleepCond);
161 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
162 lock_init(&(threads[i].splitPoints[j].lock));
165 // Allocate main thread tables to call evaluate() also when not searching
166 threads[0].pawnTable.init();
167 threads[0].materialTable.init();
169 // Create and launch all the threads, threads will go immediately to sleep
170 for (int i = 0; i <= MAX_THREADS; i++)
172 threads[i].is_searching = false;
173 threads[i].do_sleep = true;
174 threads[i].threadID = i;
176 #if defined(_MSC_VER)
177 threads[i].handle = CreateThread(NULL, 0, start_routine, (LPVOID)&threads[i], 0, NULL);
178 bool ok = (threads[i].handle != NULL);
180 bool ok = !pthread_create(&threads[i].handle, NULL, start_routine, (void*)&threads[i]);
185 std::cerr << "Failed to create thread number " << i << std::endl;
186 ::exit(EXIT_FAILURE);
192 // exit() is called to cleanly terminate the threads when the program finishes
194 void ThreadsManager::exit() {
196 for (int i = 0; i <= MAX_THREADS; i++)
198 threads[i].do_terminate = true;
199 threads[i].wake_up();
201 // Wait for thread termination
202 #if defined(_MSC_VER)
203 WaitForSingleObject(threads[i].handle, 0);
204 CloseHandle(threads[i].handle);
206 pthread_join(threads[i].handle, NULL);
209 // Now we can safely destroy associated locks and wait conditions
210 lock_destroy(&threads[i].sleepLock);
211 cond_destroy(&threads[i].sleepCond);
213 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
214 lock_destroy(&(threads[i].splitPoints[j].lock));
217 lock_destroy(&threadsLock);
218 cond_destroy(&sleepCond);
222 // available_slave_exists() tries to find an idle thread which is available as
223 // a slave for the thread with threadID 'master'.
225 bool ThreadsManager::available_slave_exists(int master) const {
227 assert(master >= 0 && master < activeThreads);
229 for (int i = 0; i < activeThreads; i++)
230 if (threads[i].is_available_to(master))
237 // split_point_finished() checks if all the slave threads of a given split
238 // point have finished searching.
240 bool ThreadsManager::split_point_finished(SplitPoint* sp) const {
242 for (int i = 0; i < activeThreads; i++)
250 // split() does the actual work of distributing the work at a node between
251 // several available threads. If it does not succeed in splitting the node
252 // (because no idle threads are available, or because we have no unused split
253 // point objects), the function immediately returns. If splitting is possible, a
254 // SplitPoint object is initialized with all the data that must be copied to the
255 // helper threads and then helper threads are told that they have been assigned
256 // work. This will cause them to instantly leave their idle loops and call
257 // search(). When all threads have returned from search() then split() returns.
260 Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value beta,
261 Value bestValue, Depth depth, Move threatMove,
262 int moveCount, MovePicker* mp, int nodeType) {
263 assert(pos.pos_is_ok());
264 assert(bestValue >= -VALUE_INFINITE);
265 assert(bestValue <= alpha);
266 assert(alpha < beta);
267 assert(beta <= VALUE_INFINITE);
268 assert(depth > DEPTH_ZERO);
269 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
270 assert(activeThreads > 1);
272 int i, master = pos.thread();
273 Thread& masterThread = threads[master];
275 // If we already have too many active split points, don't split
276 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
279 // Pick the next available split point from the split point stack
280 SplitPoint* sp = &masterThread.splitPoints[masterThread.activeSplitPoints];
282 // Initialize the split point
283 sp->parent = masterThread.splitPoint;
285 sp->is_betaCutoff = false;
287 sp->threatMove = threatMove;
290 sp->nodeType = nodeType;
291 sp->bestValue = bestValue;
293 sp->moveCount = moveCount;
298 for (i = 0; i < activeThreads; i++)
299 sp->is_slave[i] = false;
301 // If we are here it means we are not available
302 assert(masterThread.is_searching);
304 int workersCnt = 1; // At least the master is included
306 // Try to allocate available threads and ask them to start searching setting
307 // is_searching flag. This must be done under lock protection to avoid concurrent
308 // allocation of the same slave by another master.
309 lock_grab(&threadsLock);
311 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
312 if (threads[i].is_available_to(master))
315 sp->is_slave[i] = true;
316 threads[i].splitPoint = sp;
318 // This makes the slave to exit from idle_loop()
319 threads[i].is_searching = true;
321 if (useSleepingThreads)
322 threads[i].wake_up();
325 lock_release(&threadsLock);
327 // We failed to allocate even one slave, return
328 if (!Fake && workersCnt == 1)
331 masterThread.splitPoint = sp;
332 masterThread.activeSplitPoints++;
334 // Everything is set up. The master thread enters the idle loop, from which
335 // it will instantly launch a search, because its is_searching flag is set.
336 // We pass the split point as a parameter to the idle loop, which means that
337 // the thread will return from the idle loop when all slaves have finished
338 // their work at this split point.
339 masterThread.idle_loop(sp);
341 // In helpful master concept a master can help only a sub-tree of its split
342 // point, and because here is all finished is not possible master is booked.
343 assert(!masterThread.is_searching);
345 // We have returned from the idle loop, which means that all threads are
346 // finished. Note that changing state and decreasing activeSplitPoints is done
347 // under lock protection to avoid a race with Thread::is_available_to().
348 lock_grab(&threadsLock);
350 masterThread.is_searching = true;
351 masterThread.activeSplitPoints--;
353 lock_release(&threadsLock);
355 masterThread.splitPoint = sp->parent;
356 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
358 return sp->bestValue;
361 // Explicit template instantiations
362 template Value ThreadsManager::split<false>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
363 template Value ThreadsManager::split<true>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
366 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
367 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
369 void Thread::timer_loop() {
371 while (!do_terminate)
373 lock_grab(&sleepLock);
374 timed_wait(&sleepCond, &sleepLock, maxPly ? maxPly : INT_MAX);
375 lock_release(&sleepLock);
381 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
382 // milliseconds. If msec is 0 then timer is stopped.
384 void ThreadsManager::set_timer(int msec) {
386 Thread& timer = threads[MAX_THREADS];
388 lock_grab(&timer.sleepLock);
390 cond_signal(&timer.sleepCond); // Wake up and restart the timer
391 lock_release(&timer.sleepLock);
395 // Thread::main_loop() is where the main thread is parked waiting to be started
396 // when there is a new search. Main thread will launch all the slave threads.
398 void Thread::main_loop() {
402 lock_grab(&sleepLock);
404 do_sleep = true; // Always return to sleep after a search
405 is_searching = false;
407 while (do_sleep && !do_terminate)
409 cond_signal(&Threads.sleepCond); // Wake up UI thread if needed
410 cond_wait(&sleepCond, &sleepLock);
415 lock_release(&sleepLock);
420 Search::think(); // This is the search entry point
425 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
426 // thread parked in main_loop() and starting a new search. If asyncMode is true
427 // then function returns immediately, otherwise caller is blocked waiting for
428 // the search to finish.
430 void ThreadsManager::start_thinking(const Position& pos, const Search::LimitsType& limits,
431 const std::vector<Move>& searchMoves, bool asyncMode) {
432 Thread& main = threads[0];
434 lock_grab(&main.sleepLock);
436 // Wait main thread has finished before to launch a new search
437 while (!main.do_sleep)
438 cond_wait(&sleepCond, &main.sleepLock);
440 // Copy input arguments to initialize the search
441 Search::RootPosition.copy(pos, 0);
442 Search::Limits = limits;
443 Search::RootMoves = searchMoves;
445 // Reset signals before to start the new search
446 memset((void*)&Search::Signals, 0, sizeof(Search::Signals));
448 main.do_sleep = false;
449 cond_signal(&main.sleepCond); // Wake up main thread and start searching
452 cond_wait(&sleepCond, &main.sleepLock);
454 lock_release(&main.sleepLock);
458 // ThreadsManager::wait_for_stop_or_ponderhit() is called when the maximum depth
459 // is reached while the program is pondering. The point is to work around a wrinkle
460 // in the UCI protocol: When pondering, the engine is not allowed to give a
461 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
462 // wait here until one of these commands (that raise StopRequest) is sent and
463 // then return, after which the bestmove and pondermove will be printed.
465 void ThreadsManager::wait_for_stop_or_ponderhit() {
467 Search::Signals.stopOnPonderhit = true;
469 Thread& main = threads[0];
471 lock_grab(&main.sleepLock);
473 while (!Search::Signals.stop)
474 cond_wait(&main.sleepCond, &main.sleepLock);
476 lock_release(&main.sleepLock);