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 #if defined(_WIN32) || defined(_WIN64)
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() {
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 sp_count = 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 return !sp_count || (splitPoints[sp_count - 1].slavesMask & (1ULL << 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["Max Threads per Split Point"];
114 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
115 useSleepingThreads = Options["Use Sleeping Threads"];
117 set_size(Options["Threads"]);
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 cond_init(sleepCond);
152 lock_init(splitLock);
154 for (int i = 0; i <= MAX_THREADS; i++)
156 lock_init(threads[i].sleepLock);
157 cond_init(threads[i].sleepCond);
159 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
160 lock_init(threads[i].splitPoints[j].lock);
163 // Allocate main thread tables to call evaluate() also when not searching
164 threads[0].pawnTable.init();
165 threads[0].materialTable.init();
167 // Create and launch all the threads, threads will go immediately to sleep
168 for (int i = 0; i <= MAX_THREADS; i++)
170 threads[i].is_searching = false;
171 threads[i].do_sleep = (i != 0); // Avoid a race with start_thinking()
172 threads[i].threadID = i;
174 if (!thread_create(threads[i].handle, start_routine, threads[i]))
176 std::cerr << "Failed to create thread number " << i << std::endl;
177 ::exit(EXIT_FAILURE);
183 // exit() is called to cleanly terminate the threads when the program finishes
185 void ThreadsManager::exit() {
187 assert(threads[0].is_searching == false);
189 for (int i = 0; i <= MAX_THREADS; i++)
191 threads[i].do_exit = true; // Search must be already finished
192 threads[i].wake_up();
194 thread_join(threads[i].handle); // Wait for thread termination
196 lock_destroy(threads[i].sleepLock);
197 cond_destroy(threads[i].sleepCond);
199 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
200 lock_destroy(threads[i].splitPoints[j].lock);
203 lock_destroy(splitLock);
204 cond_destroy(sleepCond);
208 // available_slave_exists() tries to find an idle thread which is available as
209 // a slave for the thread with threadID 'master'.
211 bool ThreadsManager::available_slave_exists(int master) const {
213 assert(master >= 0 && master < activeThreads);
215 for (int i = 0; i < activeThreads; i++)
216 if (threads[i].is_available_to(master))
223 // split() does the actual work of distributing the work at a node between
224 // several available threads. If it does not succeed in splitting the node
225 // (because no idle threads are available, or because we have no unused split
226 // point objects), the function immediately returns. If splitting is possible, a
227 // SplitPoint object is initialized with all the data that must be copied to the
228 // helper threads and then helper threads are told that they have been assigned
229 // work. This will cause them to instantly leave their idle loops and call
230 // search(). When all threads have returned from search() then split() returns.
233 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
234 Value bestValue, Depth depth, Move threatMove,
235 int moveCount, MovePicker* mp, int nodeType) {
236 assert(pos.pos_is_ok());
237 assert(bestValue > -VALUE_INFINITE);
238 assert(bestValue <= alpha);
239 assert(alpha < beta);
240 assert(beta <= VALUE_INFINITE);
241 assert(depth > DEPTH_ZERO);
242 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
243 assert(activeThreads > 1);
245 int master = pos.thread();
246 Thread& masterThread = threads[master];
248 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
251 // Pick the next available split point from the split point stack
252 SplitPoint* sp = &masterThread.splitPoints[masterThread.activeSplitPoints];
254 sp->parent = masterThread.splitPoint;
256 sp->is_betaCutoff = false;
257 sp->slavesMask = 1ULL << master;
259 sp->threatMove = threatMove;
262 sp->nodeType = nodeType;
263 sp->bestValue = bestValue;
265 sp->moveCount = moveCount;
270 assert(masterThread.is_searching);
274 // Try to allocate available threads and ask them to start searching setting
275 // is_searching flag. This must be done under lock protection to avoid concurrent
276 // allocation of the same slave by another master.
278 lock_grab(splitLock);
280 for (int i = 0; i < activeThreads && !Fake; i++)
281 if (threads[i].is_available_to(master))
283 sp->slavesMask |= 1ULL << i;
284 threads[i].splitPoint = sp;
285 threads[i].is_searching = true; // Slave leaves idle_loop()
287 if (useSleepingThreads)
288 threads[i].wake_up();
290 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
294 masterThread.splitPoint = sp;
295 masterThread.activeSplitPoints++;
297 lock_release(splitLock);
298 lock_release(sp->lock);
300 // Everything is set up. The master thread enters the idle loop, from which
301 // it will instantly launch a search, because its is_searching flag is set.
302 // We pass the split point as a parameter to the idle loop, which means that
303 // the thread will return from the idle loop when all slaves have finished
304 // their work at this split point.
305 if (slavesCnt || Fake)
306 masterThread.idle_loop(sp);
308 // We have returned from the idle loop, which means that all threads are
309 // finished. Note that setting is_searching and decreasing activeSplitPoints is
310 // done under lock protection to avoid a race with Thread::is_available_to().
311 lock_grab(sp->lock); // To protect sp->nodes
312 lock_grab(splitLock);
314 masterThread.is_searching = true;
315 masterThread.activeSplitPoints--;
316 masterThread.splitPoint = sp->parent;
317 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
319 lock_release(splitLock);
320 lock_release(sp->lock);
322 return sp->bestValue;
325 // Explicit template instantiations
326 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
327 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
330 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
331 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
332 extern void check_time();
334 void Thread::timer_loop() {
338 lock_grab(sleepLock);
339 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
340 lock_release(sleepLock);
346 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
347 // milliseconds. If msec is 0 then timer is stopped.
349 void ThreadsManager::set_timer(int msec) {
351 Thread& timer = threads[MAX_THREADS];
353 lock_grab(timer.sleepLock);
355 cond_signal(timer.sleepCond); // Wake up and restart the timer
356 lock_release(timer.sleepLock);
360 // Thread::main_loop() is where the main thread is parked waiting to be started
361 // when there is a new search. Main thread will launch all the slave threads.
363 void Thread::main_loop() {
367 lock_grab(sleepLock);
369 do_sleep = true; // Always return to sleep after a search
370 is_searching = false;
372 while (do_sleep && !do_exit)
374 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
375 cond_wait(sleepCond, sleepLock);
380 lock_release(sleepLock);
390 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
391 // thread parked in main_loop() and starting a new search. If asyncMode is true
392 // then function returns immediately, otherwise caller is blocked waiting for
393 // the search to finish.
395 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
396 const std::set<Move>& searchMoves, bool async) {
397 Thread& main = threads[0];
399 lock_grab(main.sleepLock);
401 // Wait main thread has finished before to launch a new search
402 while (!main.do_sleep)
403 cond_wait(sleepCond, main.sleepLock);
405 // Copy input arguments to initialize the search
406 RootPosition.copy(pos, 0);
410 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
411 // set is given, with the subset of legal moves to search.
412 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
413 if (searchMoves.empty() || searchMoves.count(ml.move()))
414 RootMoves.push_back(RootMove(ml.move()));
416 // Reset signals before to start the new search
417 Signals.stopOnPonderhit = Signals.firstRootMove = false;
418 Signals.stop = Signals.failedLowAtRoot = false;
420 main.do_sleep = false;
421 cond_signal(main.sleepCond); // Wake up main thread and start searching
424 while (!main.do_sleep)
425 cond_wait(sleepCond, main.sleepLock);
427 lock_release(main.sleepLock);
431 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
432 // and to wait for the main thread finishing the search. Needed to wait exiting
433 // and terminate the threads after a 'quit' command.
435 void ThreadsManager::stop_thinking() {
437 Thread& main = threads[0];
439 Search::Signals.stop = true;
441 lock_grab(main.sleepLock);
443 cond_signal(main.sleepCond); // In case is waiting for stop or ponderhit
445 while (!main.do_sleep)
446 cond_wait(sleepCond, main.sleepLock);
448 lock_release(main.sleepLock);
452 // ThreadsManager::wait_for_stop_or_ponderhit() is called when the maximum depth
453 // is reached while the program is pondering. The point is to work around a wrinkle
454 // in the UCI protocol: When pondering, the engine is not allowed to give a
455 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
456 // wait here until one of these commands (that raise StopRequest) is sent and
457 // then return, after which the bestmove and pondermove will be printed.
459 void ThreadsManager::wait_for_stop_or_ponderhit() {
461 Signals.stopOnPonderhit = true;
463 Thread& main = threads[0];
465 lock_grab(main.sleepLock);
467 while (!Signals.stop)
468 cond_wait(main.sleepCond, main.sleepLock);
470 lock_release(main.sleepLock);