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 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
63 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
64 extern void check_time();
66 void Thread::timer_loop() {
71 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
72 lock_release(sleepLock);
78 // Thread::main_loop() is where the main thread is parked waiting to be started
79 // when there is a new search. Main thread will launch all the slave threads.
81 void Thread::main_loop() {
87 do_sleep = true; // Always return to sleep after a search
90 while (do_sleep && !do_exit)
92 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
93 cond_wait(sleepCond, sleepLock);
96 lock_release(sleepLock);
108 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
109 // or, if "sleeping threads" is used, when there is some work to do.
111 void Thread::wake_up() {
113 lock_grab(sleepLock);
114 cond_signal(sleepCond);
115 lock_release(sleepLock);
119 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
120 // reached while the program is pondering. The point is to work around a wrinkle
121 // in the UCI protocol: When pondering, the engine is not allowed to give a
122 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
123 // wait here until one of these commands (that raise StopRequest) is sent and
124 // then return, after which the bestmove and pondermove will be printed.
126 void Thread::wait_for_stop_or_ponderhit() {
128 Signals.stopOnPonderhit = true;
130 lock_grab(sleepLock);
132 while (!Signals.stop)
133 cond_wait(sleepCond, sleepLock);
135 lock_release(sleepLock);
139 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
140 // active split point, or in some ancestor of the split point.
142 bool Thread::cutoff_occurred() const {
144 for (SplitPoint* sp = splitPoint; sp; sp = sp->parent)
152 // is_available_to() checks whether the thread is available to help the thread with
153 // threadID "master" at a split point. An obvious requirement is that thread must be
154 // idle. With more than two threads, this is not by itself sufficient: If the thread
155 // is the master of some active split point, it is only available as a slave to the
156 // threads which are busy searching the split point at the top of "slave"'s split
157 // point stack (the "helpful master concept" in YBWC terminology).
159 bool Thread::is_available_to(int master) const {
164 // Make a local copy to be sure doesn't become zero under our feet while
165 // testing next condition and so leading to an out of bound access.
166 int sp_count = activeSplitPoints;
168 // No active split points means that the thread is available as a slave for any
169 // other thread otherwise apply the "helpful master" concept if possible.
170 return !sp_count || (splitPoints[sp_count - 1].slavesMask & (1ULL << master));
174 // read_uci_options() updates number of active threads and other parameters
175 // according to the UCI options values. It is called before to start a new search.
177 void ThreadsManager::read_uci_options() {
179 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
180 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
181 useSleepingThreads = Options["Use Sleeping Threads"];
183 set_size(Options["Threads"]);
187 // set_size() changes the number of active threads and raises do_sleep flag for
188 // all the unused threads that will go immediately to sleep.
190 void ThreadsManager::set_size(int cnt) {
192 assert(cnt > 0 && cnt <= MAX_THREADS);
196 for (int i = 1; i < MAX_THREADS; i++) // Ignore main thread
197 if (i < activeThreads)
199 // Dynamically allocate pawn and material hash tables according to the
200 // number of active threads. This avoids preallocating memory for all
201 // possible threads if only few are used.
202 threads[i].pawnTable.init();
203 threads[i].materialTable.init();
205 threads[i].do_sleep = false;
208 threads[i].do_sleep = true;
212 // init() is called during startup. Initializes locks and condition variables
213 // and launches all threads sending them immediately to sleep.
215 void ThreadsManager::init() {
217 cond_init(sleepCond);
218 lock_init(splitLock);
220 for (int i = 0; i <= MAX_THREADS; i++)
222 lock_init(threads[i].sleepLock);
223 cond_init(threads[i].sleepCond);
225 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
226 lock_init(threads[i].splitPoints[j].lock);
229 // Allocate main thread tables to call evaluate() also when not searching
230 threads[0].pawnTable.init();
231 threads[0].materialTable.init();
233 // Create and launch all the threads, threads will go immediately to sleep
234 for (int i = 0; i <= MAX_THREADS; i++)
236 threads[i].is_searching = false;
237 threads[i].do_sleep = (i != 0); // Avoid a race with start_thinking()
238 threads[i].threadID = i;
240 if (!thread_create(threads[i].handle, start_routine, threads[i]))
242 std::cerr << "Failed to create thread number " << i << std::endl;
243 ::exit(EXIT_FAILURE);
249 // exit() is called to cleanly terminate the threads when the program finishes
251 void ThreadsManager::exit() {
253 for (int i = 0; i <= MAX_THREADS; i++)
255 assert(threads[i].do_sleep);
257 threads[i].do_exit = true; // Search must be already finished
258 threads[i].wake_up();
260 thread_join(threads[i].handle); // Wait for thread termination
262 lock_destroy(threads[i].sleepLock);
263 cond_destroy(threads[i].sleepCond);
265 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
266 lock_destroy(threads[i].splitPoints[j].lock);
269 lock_destroy(splitLock);
270 cond_destroy(sleepCond);
274 // available_slave_exists() tries to find an idle thread which is available as
275 // a slave for the thread with threadID 'master'.
277 bool ThreadsManager::available_slave_exists(int master) const {
279 assert(master >= 0 && master < activeThreads);
281 for (int i = 0; i < activeThreads; i++)
282 if (threads[i].is_available_to(master))
289 // split() does the actual work of distributing the work at a node between
290 // several available threads. If it does not succeed in splitting the node
291 // (because no idle threads are available, or because we have no unused split
292 // point objects), the function immediately returns. If splitting is possible, a
293 // SplitPoint object is initialized with all the data that must be copied to the
294 // helper threads and then helper threads are told that they have been assigned
295 // work. This will cause them to instantly leave their idle loops and call
296 // search(). When all threads have returned from search() then split() returns.
299 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
300 Value bestValue, Depth depth, Move threatMove,
301 int moveCount, MovePicker* mp, int nodeType) {
302 assert(pos.pos_is_ok());
303 assert(bestValue > -VALUE_INFINITE);
304 assert(bestValue <= alpha);
305 assert(alpha < beta);
306 assert(beta <= VALUE_INFINITE);
307 assert(depth > DEPTH_ZERO);
308 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
309 assert(activeThreads > 1);
311 int master = pos.thread();
312 Thread& masterThread = threads[master];
314 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
317 // Pick the next available split point from the split point stack
318 SplitPoint* sp = &masterThread.splitPoints[masterThread.activeSplitPoints];
320 sp->parent = masterThread.splitPoint;
323 sp->slavesMask = 1ULL << master;
325 sp->threatMove = threatMove;
328 sp->nodeType = nodeType;
329 sp->bestValue = bestValue;
331 sp->moveCount = moveCount;
336 assert(masterThread.is_searching);
340 // Try to allocate available threads and ask them to start searching setting
341 // is_searching flag. This must be done under lock protection to avoid concurrent
342 // allocation of the same slave by another master.
344 lock_grab(splitLock);
346 for (int i = 0; i < activeThreads && !Fake; i++)
347 if (threads[i].is_available_to(master))
349 sp->slavesMask |= 1ULL << i;
350 threads[i].splitPoint = sp;
351 threads[i].is_searching = true; // Slave leaves idle_loop()
353 if (useSleepingThreads)
354 threads[i].wake_up();
356 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
360 masterThread.splitPoint = sp;
361 masterThread.activeSplitPoints++;
363 lock_release(splitLock);
364 lock_release(sp->lock);
366 // Everything is set up. The master thread enters the idle loop, from which
367 // it will instantly launch a search, because its is_searching flag is set.
368 // We pass the split point as a parameter to the idle loop, which means that
369 // the thread will return from the idle loop when all slaves have finished
370 // their work at this split point.
371 if (slavesCnt || Fake)
372 masterThread.idle_loop(sp);
374 // We have returned from the idle loop, which means that all threads are
375 // finished. Note that setting is_searching and decreasing activeSplitPoints is
376 // done under lock protection to avoid a race with Thread::is_available_to().
377 lock_grab(sp->lock); // To protect sp->nodes
378 lock_grab(splitLock);
380 masterThread.is_searching = true;
381 masterThread.activeSplitPoints--;
382 masterThread.splitPoint = sp->parent;
383 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
385 lock_release(splitLock);
386 lock_release(sp->lock);
388 return sp->bestValue;
391 // Explicit template instantiations
392 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
393 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
396 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
397 // milliseconds. If msec is 0 then timer is stopped.
399 void ThreadsManager::set_timer(int msec) {
401 Thread& timer = threads[MAX_THREADS];
403 lock_grab(timer.sleepLock);
405 cond_signal(timer.sleepCond); // Wake up and restart the timer
406 lock_release(timer.sleepLock);
410 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
411 // thread parked in main_loop() and starting a new search. If asyncMode is true
412 // then function returns immediately, otherwise caller is blocked waiting for
413 // the search to finish.
415 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
416 const std::set<Move>& searchMoves, bool async) {
417 Thread& main = threads[0];
419 lock_grab(main.sleepLock);
421 // Wait main thread has finished before to launch a new search
422 while (!main.do_sleep)
423 cond_wait(sleepCond, main.sleepLock);
425 // Copy input arguments to initialize the search
426 RootPosition.copy(pos, 0);
430 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
431 // set is given, with the subset of legal moves to search.
432 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
433 if (searchMoves.empty() || searchMoves.count(ml.move()))
434 RootMoves.push_back(RootMove(ml.move()));
436 // Reset signals before to start the new search
437 Signals.stopOnPonderhit = Signals.firstRootMove = false;
438 Signals.stop = Signals.failedLowAtRoot = false;
440 main.do_sleep = false;
441 cond_signal(main.sleepCond); // Wake up main thread and start searching
444 while (!main.do_sleep)
445 cond_wait(sleepCond, main.sleepLock);
447 lock_release(main.sleepLock);
451 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
452 // and to wait for the main thread finishing the search. Needed to wait exiting
453 // and terminate the threads after a 'quit' command.
455 void ThreadsManager::stop_thinking() {
457 Thread& main = threads[0];
459 Search::Signals.stop = true;
461 lock_grab(main.sleepLock);
463 cond_signal(main.sleepCond); // In case is waiting for stop or ponderhit
465 while (!main.do_sleep)
466 cond_wait(sleepCond, main.sleepLock);
468 lock_release(main.sleepLock);