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/>.
24 #include "ucioption.h"
26 using namespace Search;
28 ThreadsManager Threads; // Global object
30 namespace { extern "C" {
32 // start_routine() is the C function which is called when a new thread
33 // is launched. It simply calls idle_loop() of the supplied thread. The first
34 // and last thread are special. First one is the main search thread while the
35 // last one mimics a timer, they run in main_loop() and timer_loop().
38 DWORD WINAPI start_routine(LPVOID thread) {
40 void* start_routine(void* thread) {
43 Thread* th = (Thread*)thread;
45 if (th->threadID == 0)
48 else if (th->threadID == MAX_THREADS)
60 // wake_up() wakes up the thread, normally at the beginning of the search or,
61 // if "sleeping threads" is used, when there is some work to do.
63 void Thread::wake_up() {
65 lock_grab(&sleepLock);
66 cond_signal(&sleepCond);
67 lock_release(&sleepLock);
71 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
72 // active split point, or in some ancestor of the split point.
74 bool Thread::cutoff_occurred() const {
76 for (SplitPoint* sp = splitPoint; sp; sp = sp->parent)
77 if (sp->is_betaCutoff)
84 // is_available_to() checks whether the thread is available to help the thread with
85 // threadID "master" at a split point. An obvious requirement is that thread must be
86 // idle. With more than two threads, this is not by itself sufficient: If the thread
87 // is the master of some active split point, it is only available as a slave to the
88 // threads which are busy searching the split point at the top of "slave"'s split
89 // point stack (the "helpful master concept" in YBWC terminology).
91 bool Thread::is_available_to(int master) const {
96 // Make a local copy to be sure doesn't become zero under our feet while
97 // testing next condition and so leading to an out of bound access.
98 int localActiveSplitPoints = activeSplitPoints;
100 // No active split points means that the thread is available as a slave for any
101 // other thread otherwise apply the "helpful master" concept if possible.
102 if ( !localActiveSplitPoints
103 || splitPoints[localActiveSplitPoints - 1].is_slave[master])
110 // read_uci_options() updates number of active threads and other parameters
111 // according to the UCI options values. It is called before to start a new search.
113 void ThreadsManager::read_uci_options() {
115 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
116 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
117 useSleepingThreads = Options["Use Sleeping Threads"];
119 set_size(Options["Threads"]);
123 // set_size() changes the number of active threads and raises do_sleep flag for
124 // all the unused threads that will go immediately to sleep.
126 void ThreadsManager::set_size(int cnt) {
128 assert(cnt > 0 && cnt <= MAX_THREADS);
132 for (int i = 1; i < MAX_THREADS; i++) // Ignore main thread
133 if (i < activeThreads)
135 // Dynamically allocate pawn and material hash tables according to the
136 // number of active threads. This avoids preallocating memory for all
137 // possible threads if only few are used.
138 threads[i].pawnTable.init();
139 threads[i].materialTable.init();
141 threads[i].do_sleep = false;
144 threads[i].do_sleep = true;
148 // init() is called during startup. Initializes locks and condition variables
149 // and launches all threads sending them immediately to sleep.
151 void ThreadsManager::init() {
153 // Initialize sleep condition and lock used by thread manager
154 cond_init(&sleepCond);
155 lock_init(&threadsLock);
157 // Initialize thread's sleep conditions and split point locks
158 for (int i = 0; i <= MAX_THREADS; i++)
160 lock_init(&threads[i].sleepLock);
161 cond_init(&threads[i].sleepCond);
163 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
164 lock_init(&(threads[i].splitPoints[j].lock));
167 // Allocate main thread tables to call evaluate() also when not searching
168 threads[0].pawnTable.init();
169 threads[0].materialTable.init();
171 // Create and launch all the threads, threads will go immediately to sleep
172 for (int i = 0; i <= MAX_THREADS; i++)
174 threads[i].is_searching = false;
175 threads[i].do_sleep = (i != 0); // Avoid a race with start_thinking()
176 threads[i].threadID = i;
178 #if defined(_MSC_VER)
179 threads[i].handle = CreateThread(NULL, 0, start_routine, &threads[i], 0, NULL);
180 bool ok = (threads[i].handle != NULL);
182 bool ok = !pthread_create(&threads[i].handle, NULL, start_routine, &threads[i]);
187 std::cerr << "Failed to create thread number " << i << std::endl;
188 ::exit(EXIT_FAILURE);
194 // exit() is called to cleanly terminate the threads when the program finishes
196 void ThreadsManager::exit() {
198 for (int i = 0; i <= MAX_THREADS; i++)
200 threads[i].do_terminate = true; // Search must be already finished
201 threads[i].wake_up();
203 // Wait for thread termination
204 #if defined(_MSC_VER)
205 WaitForSingleObject(threads[i].handle, INFINITE);
206 CloseHandle(threads[i].handle);
208 pthread_join(threads[i].handle, NULL);
211 // Now we can safely destroy associated locks and wait conditions
212 lock_destroy(&threads[i].sleepLock);
213 cond_destroy(&threads[i].sleepCond);
215 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
216 lock_destroy(&(threads[i].splitPoints[j].lock));
219 lock_destroy(&threadsLock);
220 cond_destroy(&sleepCond);
224 // available_slave_exists() tries to find an idle thread which is available as
225 // a slave for the thread with threadID 'master'.
227 bool ThreadsManager::available_slave_exists(int master) const {
229 assert(master >= 0 && master < activeThreads);
231 for (int i = 0; i < activeThreads; i++)
232 if (threads[i].is_available_to(master))
239 // split_point_finished() checks if all the slave threads of a given split
240 // point have finished searching.
242 bool ThreadsManager::split_point_finished(SplitPoint* sp) const {
244 for (int i = 0; i < activeThreads; i++)
252 // split() does the actual work of distributing the work at a node between
253 // several available threads. If it does not succeed in splitting the node
254 // (because no idle threads are available, or because we have no unused split
255 // point objects), the function immediately returns. If splitting is possible, a
256 // SplitPoint object is initialized with all the data that must be copied to the
257 // helper threads and then helper threads are told that they have been assigned
258 // work. This will cause them to instantly leave their idle loops and call
259 // search(). When all threads have returned from search() then split() returns.
262 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
263 Value bestValue, Depth depth, Move threatMove,
264 int moveCount, MovePicker* mp, int nodeType) {
265 assert(pos.pos_is_ok());
266 assert(bestValue > -VALUE_INFINITE);
267 assert(bestValue <= alpha);
268 assert(alpha < beta);
269 assert(beta <= VALUE_INFINITE);
270 assert(depth > DEPTH_ZERO);
271 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
272 assert(activeThreads > 1);
274 int i, master = pos.thread();
275 Thread& masterThread = threads[master];
277 // If we already have too many active split points, don't split
278 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
281 // Pick the next available split point from the split point stack
282 SplitPoint* sp = &masterThread.splitPoints[masterThread.activeSplitPoints];
284 // Initialize the split point
285 sp->parent = masterThread.splitPoint;
287 sp->is_betaCutoff = false;
289 sp->threatMove = threatMove;
292 sp->nodeType = nodeType;
293 sp->bestValue = bestValue;
295 sp->moveCount = moveCount;
300 for (i = 0; i < activeThreads; i++)
301 sp->is_slave[i] = false;
303 // If we are here it means we are not available
304 assert(masterThread.is_searching);
306 int workersCnt = 1; // At least the master is included
308 // Try to allocate available threads and ask them to start searching setting
309 // is_searching flag. This must be done under lock protection to avoid concurrent
310 // allocation of the same slave by another master.
311 lock_grab(&threadsLock);
313 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
314 if (threads[i].is_available_to(master))
317 sp->is_slave[i] = true;
318 threads[i].splitPoint = sp;
320 // This makes the slave to exit from idle_loop()
321 threads[i].is_searching = true;
323 if (useSleepingThreads)
324 threads[i].wake_up();
327 lock_release(&threadsLock);
329 // We failed to allocate even one slave, return
330 if (!Fake && workersCnt == 1)
333 masterThread.splitPoint = sp;
334 masterThread.activeSplitPoints++;
336 // Everything is set up. The master thread enters the idle loop, from which
337 // it will instantly launch a search, because its is_searching flag is set.
338 // We pass the split point as a parameter to the idle loop, which means that
339 // the thread will return from the idle loop when all slaves have finished
340 // their work at this split point.
341 masterThread.idle_loop(sp);
343 // In helpful master concept a master can help only a sub-tree of its split
344 // point, and because here is all finished is not possible master is booked.
345 assert(!masterThread.is_searching);
347 // We have returned from the idle loop, which means that all threads are
348 // finished. Note that changing state and decreasing activeSplitPoints is done
349 // under lock protection to avoid a race with Thread::is_available_to().
350 lock_grab(&threadsLock);
352 masterThread.is_searching = true;
353 masterThread.activeSplitPoints--;
355 lock_release(&threadsLock);
357 masterThread.splitPoint = sp->parent;
358 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
360 return sp->bestValue;
363 // Explicit template instantiations
364 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
365 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
368 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
369 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
370 extern void do_timer_event();
372 void Thread::timer_loop() {
374 while (!do_terminate)
376 lock_grab(&sleepLock);
377 timed_wait(&sleepCond, &sleepLock, maxPly ? maxPly : INT_MAX);
378 lock_release(&sleepLock);
384 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
385 // milliseconds. If msec is 0 then timer is stopped.
387 void ThreadsManager::set_timer(int msec) {
389 Thread& timer = threads[MAX_THREADS];
391 lock_grab(&timer.sleepLock);
393 cond_signal(&timer.sleepCond); // Wake up and restart the timer
394 lock_release(&timer.sleepLock);
398 // Thread::main_loop() is where the main thread is parked waiting to be started
399 // when there is a new search. Main thread will launch all the slave threads.
401 void Thread::main_loop() {
405 lock_grab(&sleepLock);
407 do_sleep = true; // Always return to sleep after a search
408 is_searching = false;
410 while (do_sleep && !do_terminate)
412 cond_signal(&Threads.sleepCond); // Wake up UI thread if needed
413 cond_wait(&sleepCond, &sleepLock);
418 lock_release(&sleepLock);
423 think(); // This is the search entry point
428 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
429 // thread parked in main_loop() and starting a new search. If asyncMode is true
430 // then function returns immediately, otherwise caller is blocked waiting for
431 // the search to finish.
433 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
434 const std::vector<Move>& searchMoves, bool asyncMode) {
435 Thread& main = threads[0];
437 lock_grab(&main.sleepLock);
439 // Wait main thread has finished before to launch a new search
440 while (!main.do_sleep)
441 cond_wait(&sleepCond, &main.sleepLock);
443 // Copy input arguments to initialize the search
444 RootPosition.copy(pos, 0);
446 SearchMoves = searchMoves;
448 // Reset signals before to start the new search
449 memset((void*)&Signals, 0, sizeof(Signals));
451 main.do_sleep = false;
452 cond_signal(&main.sleepCond); // Wake up main thread and start searching
455 while (!main.do_sleep)
456 cond_wait(&sleepCond, &main.sleepLock);
458 lock_release(&main.sleepLock);
462 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
463 // and to wait for the main thread finishing the search. Needed to wait exiting
464 // and terminate the threads after a 'quit' command.
466 void ThreadsManager::stop_thinking() {
468 Thread& main = threads[0];
470 Search::Signals.stop = true;
472 lock_grab(&main.sleepLock);
474 cond_signal(&main.sleepCond); // In case is waiting for stop or ponderhit
476 while (!main.do_sleep)
477 cond_wait(&sleepCond, &main.sleepLock);
479 lock_release(&main.sleepLock);
483 // ThreadsManager::wait_for_stop_or_ponderhit() is called when the maximum depth
484 // is reached while the program is pondering. The point is to work around a wrinkle
485 // in the UCI protocol: When pondering, the engine is not allowed to give a
486 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
487 // wait here until one of these commands (that raise StopRequest) is sent and
488 // then return, after which the bestmove and pondermove will be printed.
490 void ThreadsManager::wait_for_stop_or_ponderhit() {
492 Signals.stopOnPonderhit = true;
494 Thread& main = threads[0];
496 lock_grab(&main.sleepLock);
498 while (!Signals.stop)
499 cond_wait(&main.sleepCond, &main.sleepLock);
501 lock_release(&main.sleepLock);