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 definition
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
32 // last two threads are dedicated to read input from GUI and to mimic a
33 // timer, so they run in listener_loop() and timer_loop() respectively.
36 DWORD WINAPI start_routine(LPVOID thread) {
38 void* start_routine(void* thread) {
41 if (((Thread*)thread)->threadID == 0)
42 ((Thread*)thread)->main_loop();
44 else if (((Thread*)thread)->threadID == MAX_THREADS)
45 ((Thread*)thread)->timer_loop();
47 ((Thread*)thread)->idle_loop(NULL);
55 // wake_up() wakes up the thread, normally at the beginning of the search or,
56 // if "sleeping threads" is used, when there is some work to do.
58 void Thread::wake_up() {
60 lock_grab(&sleepLock);
61 cond_signal(&sleepCond);
62 lock_release(&sleepLock);
66 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
67 // active split point, or in some ancestor of the split point.
69 bool Thread::cutoff_occurred() const {
71 for (SplitPoint* sp = splitPoint; sp; sp = sp->parent)
72 if (sp->is_betaCutoff)
78 // is_available_to() checks whether the thread is available to help the thread with
79 // threadID "master" at a split point. An obvious requirement is that thread must be
80 // idle. With more than two threads, this is not by itself sufficient: If the thread
81 // is the master of some active split point, it is only available as a slave to the
82 // threads which are busy searching the split point at the top of "slave"'s split
83 // point stack (the "helpful master concept" in YBWC terminology).
85 bool Thread::is_available_to(int master) const {
90 // Make a local copy to be sure doesn't become zero under our feet while
91 // testing next condition and so leading to an out of bound access.
92 int localActiveSplitPoints = activeSplitPoints;
94 // No active split points means that the thread is available as a slave for any
95 // other thread otherwise apply the "helpful master" concept if possible.
96 if ( !localActiveSplitPoints
97 || splitPoints[localActiveSplitPoints - 1].is_slave[master])
104 // read_uci_options() updates number of active threads and other internal
105 // parameters according to the UCI options values. It is called before
106 // to start a new search.
108 void ThreadsManager::read_uci_options() {
110 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
111 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
112 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
114 set_size(Options["Threads"].value<int>());
118 // set_size() changes the number of active threads and raises do_sleep flag for
119 // all the unused threads that will go immediately to sleep.
121 void ThreadsManager::set_size(int cnt) {
123 assert(cnt > 0 && cnt <= MAX_THREADS);
127 for (int i = 1; i < MAX_THREADS; i++) // Ignore main thread
128 if (i < activeThreads)
130 // Dynamically allocate pawn and material hash tables according to the
131 // number of active threads. This avoids preallocating memory for all
132 // possible threads if only few are used as, for instance, on mobile
133 // devices where memory is scarce and allocating for MAX_THREADS could
134 // even result in a crash.
135 threads[i].pawnTable.init();
136 threads[i].materialTable.init();
138 threads[i].do_sleep = false;
141 threads[i].do_sleep = true;
145 // init() is called during startup. Initializes locks and condition variables
146 // and launches all threads sending them immediately to sleep.
148 void ThreadsManager::init() {
150 // Initialize sleep condition used to block waiting for end of searching
151 cond_init(&sleepCond);
153 // Initialize threads lock, used when allocating slaves during splitting
154 lock_init(&threadsLock);
156 // Initialize sleep and split point locks
157 for (int i = 0; i <= MAX_THREADS; i++)
159 lock_init(&threads[i].sleepLock);
160 cond_init(&threads[i].sleepCond);
162 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
163 lock_init(&(threads[i].splitPoints[j].lock));
166 // Initialize main thread's associated data
167 threads[0].pawnTable.init();
168 threads[0].materialTable.init();
170 // Create and launch all the threads, threads will go immediately to sleep
171 for (int i = 0; i <= MAX_THREADS; i++)
173 threads[i].is_searching = false;
174 threads[i].do_sleep = true;
175 threads[i].threadID = i;
177 #if defined(_MSC_VER)
178 threads[i].handle = CreateThread(NULL, 0, start_routine, (LPVOID)&threads[i], 0, NULL);
179 bool ok = (threads[i].handle != NULL);
181 bool ok = (pthread_create(&threads[i].handle, NULL, start_routine, (void*)&threads[i]) == 0);
186 std::cerr << "Failed to create thread number " << i << std::endl;
187 ::exit(EXIT_FAILURE);
193 // exit() is called to cleanly terminate the threads when the program finishes
195 void ThreadsManager::exit() {
197 for (int i = 0; i <= MAX_THREADS; i++)
199 threads[i].do_terminate = true;
200 threads[i].wake_up();
202 // Wait for slave termination
203 #if defined(_MSC_VER)
204 WaitForSingleObject(threads[i].handle, 0);
205 CloseHandle(threads[i].handle);
207 pthread_join(threads[i].handle, NULL);
210 // Now we can safely destroy locks and wait conditions
211 lock_destroy(&threads[i].sleepLock);
212 cond_destroy(&threads[i].sleepCond);
214 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
215 lock_destroy(&(threads[i].splitPoints[j].lock));
218 lock_destroy(&threadsLock);
219 cond_destroy(&sleepCond);
223 // available_slave_exists() tries to find an idle thread which is available as
224 // a slave for the thread with threadID "master".
226 bool ThreadsManager::available_slave_exists(int master) const {
228 assert(master >= 0 && master < activeThreads);
230 for (int i = 0; i < activeThreads; i++)
231 if (i != master && threads[i].is_available_to(master))
238 // split_point_finished() checks if all the slave threads of a given split
239 // point have finished searching.
241 bool ThreadsManager::split_point_finished(SplitPoint* sp) const {
243 for (int i = 0; i < activeThreads; i++)
251 // split() does the actual work of distributing the work at a node between
252 // several available threads. If it does not succeed in splitting the
253 // node (because no idle threads are available, or because we have no unused
254 // split point objects), the function immediately returns. If splitting is
255 // possible, a SplitPoint object is initialized with all the data that must be
256 // copied to the helper threads and we tell our helper threads that they have
257 // been assigned work. This will cause them to instantly leave their idle loops and
258 // call search().When all threads have returned from search() then split() returns.
261 Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value beta,
262 Value bestValue, Depth depth, Move threatMove,
263 int moveCount, MovePicker* mp, int nodeType) {
264 assert(pos.pos_is_ok());
265 assert(bestValue >= -VALUE_INFINITE);
266 assert(bestValue <= alpha);
267 assert(alpha < beta);
268 assert(beta <= VALUE_INFINITE);
269 assert(depth > DEPTH_ZERO);
270 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
271 assert(activeThreads > 1);
273 int i, master = pos.thread();
274 Thread& masterThread = threads[master];
276 // If we already have too many active split points, don't split
277 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
280 // Pick the next available split point object from the split point stack
281 SplitPoint* sp = masterThread.splitPoints + masterThread.activeSplitPoints;
283 // Initialize the split point object
284 sp->parent = masterThread.splitPoint;
286 sp->is_betaCutoff = false;
288 sp->threatMove = threatMove;
291 sp->nodeType = nodeType;
292 sp->bestValue = bestValue;
294 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 // the state to Thread::WORKISWAITING, this must be done under lock protection
308 // to avoid concurrent allocation of the same slave by another master.
309 lock_grab(&threadsLock);
311 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
312 if (i != master && 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, and
342 // 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
367 // and then calls do_timer_event().
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
406 is_searching = false;
408 while (do_sleep && !do_terminate)
410 cond_signal(&Threads.sleepCond); // Wake up UI thread if needed
411 cond_wait(&sleepCond, &sleepLock);
416 lock_release(&sleepLock);
426 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
427 // thread parked in main_loop() and starting a new search. If asyncMode is true
428 // then function returns immediately, otherwise caller is blocked waiting for
429 // the search to finish.
431 void ThreadsManager::start_thinking(bool asyncMode) {
433 Thread& main = threads[0];
435 lock_grab(&main.sleepLock);
437 // Wait main thread has finished before to launch a new search
438 while (!main.do_sleep)
439 cond_wait(&sleepCond, &main.sleepLock);
441 // Reset signals before to start the search
442 memset((void*)&Search::Signals, 0, sizeof(Search::Signals));
444 main.do_sleep = false;
445 cond_signal(&main.sleepCond); // Wake up main thread
448 cond_wait(&sleepCond, &main.sleepLock);
450 lock_release(&main.sleepLock);
454 // ThreadsManager::wait_for_stop_or_ponderhit() is called when the maximum depth
455 // is reached while the program is pondering. The point is to work around a wrinkle
456 // in the UCI protocol: When pondering, the engine is not allowed to give a
457 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
458 // We simply wait here until one of these commands (that raise StopRequest) is
459 // sent, and return, after which the bestmove and pondermove will be printed.
461 void ThreadsManager::wait_for_stop_or_ponderhit() {
463 Search::Signals.stopOnPonderhit = true;
465 Thread& main = threads[0];
467 lock_grab(&main.sleepLock);
469 while (!Search::Signals.stop)
470 cond_wait(&main.sleepCond, &main.sleepLock);
472 lock_release(&main.sleepLock);