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
31 THREAD_LOCAL Thread* this_thread; // Thread local variable
33 namespace { extern "C" {
35 // start_routine() is the C function which is called when a new thread
36 // is launched. It is a wrapper to member function pointed by start_fn.
38 long start_routine(Thread* th) {
40 this_thread = th; // Save pointer into thread local storage
41 (th->*(th->start_fn))();
47 // Thread c'tor starts a newly-created thread of execution that will call
48 // the idle loop function pointed by start_fn going immediately to sleep.
50 Thread::Thread(Fn fn) {
52 is_searching = do_exit = false;
53 maxPly = splitPointsCnt = 0;
58 do_sleep = (fn != &Thread::main_loop); // Avoid a race with start_searching()
63 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
64 lock_init(splitPoints[j].lock);
66 if (!thread_create(handle, start_routine, this))
68 std::cerr << "Failed to create thread number " << idx << std::endl;
74 // Thread d'tor waits for thread termination before to return.
80 do_exit = true; // Search must be already finished
83 thread_join(handle); // Wait for thread termination
85 lock_destroy(sleepLock);
86 cond_destroy(sleepCond);
88 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
89 lock_destroy(splitPoints[j].lock);
93 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
94 // then calls check_time(). If maxPly is 0 thread sleeps until is woken up.
95 extern void check_time();
97 void Thread::timer_loop() {
101 lock_grab(sleepLock);
102 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
103 lock_release(sleepLock);
109 // Thread::main_loop() is where the main thread is parked waiting to be started
110 // when there is a new search. Main thread will launch all the slave threads.
112 void Thread::main_loop() {
116 lock_grab(sleepLock);
118 do_sleep = true; // Always return to sleep after a search
119 is_searching = false;
121 while (do_sleep && !do_exit)
123 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
124 cond_wait(sleepCond, sleepLock);
127 lock_release(sleepLock);
139 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
140 // or, if "sleeping threads" is used at split time.
142 void Thread::wake_up() {
144 lock_grab(sleepLock);
145 cond_signal(sleepCond);
146 lock_release(sleepLock);
150 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
151 // reached while the program is pondering. The point is to work around a wrinkle
152 // in the UCI protocol: When pondering, the engine is not allowed to give a
153 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
154 // wait here until one of these commands (that raise StopRequest) is sent and
155 // then return, after which the bestmove and pondermove will be printed.
157 void Thread::wait_for_stop_or_ponderhit() {
159 Signals.stopOnPonderhit = true;
161 lock_grab(sleepLock);
162 while (!Signals.stop) cond_wait(sleepCond, sleepLock);
163 lock_release(sleepLock);
167 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
168 // current active split point, or in some ancestor of the split point.
170 bool Thread::cutoff_occurred() const {
172 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
180 // Thread::is_available_to() checks whether the thread is available to help the
181 // thread 'master' at a split point. An obvious requirement is that thread must
182 // be idle. With more than two threads, this is not sufficient: If the thread is
183 // the master of some active split point, it is only available as a slave to the
184 // slaves which are busy searching the split point at the top of slaves split
185 // point stack (the "helpful master concept" in YBWC terminology).
187 bool Thread::is_available_to(Thread* master) const {
192 // Make a local copy to be sure doesn't become zero under our feet while
193 // testing next condition and so leading to an out of bound access.
194 int spCnt = splitPointsCnt;
196 // No active split points means that the thread is available as a slave for any
197 // other thread otherwise apply the "helpful master" concept if possible.
198 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master->idx));
202 // init() is called at startup. Initializes lock and condition variable and
203 // launches requested threads sending them immediately to sleep. We cannot use
204 // a c'tor becuase Threads is a static object and we need a fully initialized
205 // engine at this point due to allocation of endgames in Thread c'tor.
207 void ThreadsManager::init() {
209 cond_init(sleepCond);
210 lock_init(splitLock);
211 timer = new Thread(&Thread::timer_loop);
212 threads.push_back(new Thread(&Thread::main_loop));
213 this_thread = main_thread(); // Use main thread's resources
218 // d'tor cleanly terminates the threads when the program exits.
220 ThreadsManager::~ThreadsManager() {
222 for (int i = 0; i < size(); i++)
226 lock_destroy(splitLock);
227 cond_destroy(sleepCond);
231 // read_uci_options() updates internal threads parameters from the corresponding
232 // UCI options and creates/destroys threads to match the requested number. Thread
233 // objects are dynamically allocated to avoid creating in advance all possible
234 // threads, with included pawns and material tables, if only few are used.
236 void ThreadsManager::read_uci_options() {
238 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
239 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
240 useSleepingThreads = Options["Use Sleeping Threads"];
241 int requested = Options["Threads"];
243 assert(requested > 0);
245 while (size() < requested)
246 threads.push_back(new Thread(&Thread::idle_loop));
248 while (size() > requested)
250 delete threads.back();
256 // wake_up() is called before a new search to start the threads that are waiting
257 // on the sleep condition and to reset maxPly. When useSleepingThreads is set
258 // threads will be woken up at split time.
260 void ThreadsManager::wake_up() const {
262 for (int i = 0; i < size(); i++)
264 threads[i]->maxPly = 0;
265 threads[i]->do_sleep = false;
267 if (!useSleepingThreads)
268 threads[i]->wake_up();
273 // sleep() is called after the search finishes to ask all the threads but the
274 // main one to go waiting on a sleep condition.
276 void ThreadsManager::sleep() const {
278 for (int i = 1; i < size(); i++) // Main thread will go to sleep by itself
279 threads[i]->do_sleep = true; // to avoid a race with start_searching()
283 // available_slave_exists() tries to find an idle thread which is available as
284 // a slave for the thread 'master'.
286 bool ThreadsManager::available_slave_exists(Thread* master) const {
288 for (int i = 0; i < size(); i++)
289 if (threads[i]->is_available_to(master))
296 // split() does the actual work of distributing the work at a node between
297 // several available threads. If it does not succeed in splitting the node
298 // (because no idle threads are available, or because we have no unused split
299 // point objects), the function immediately returns. If splitting is possible, a
300 // SplitPoint object is initialized with all the data that must be copied to the
301 // helper threads and then helper threads are told that they have been assigned
302 // work. This will cause them to instantly leave their idle loops and call
303 // search(). When all threads have returned from search() then split() returns.
306 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
307 Value bestValue, Move* bestMove, Depth depth,
308 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
309 assert(pos.pos_is_ok());
310 assert(bestValue > -VALUE_INFINITE);
311 assert(bestValue <= alpha);
312 assert(alpha < beta);
313 assert(beta <= VALUE_INFINITE);
314 assert(depth > DEPTH_ZERO);
316 Thread* master = this_thread;
318 if (master->splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
321 // Pick the next available split point from the split point stack
322 SplitPoint* sp = &master->splitPoints[master->splitPointsCnt++];
324 sp->parent = master->curSplitPoint;
327 sp->slavesMask = 1ULL << master->idx;
329 sp->bestMove = *bestMove;
330 sp->threatMove = threatMove;
333 sp->nodeType = nodeType;
334 sp->bestValue = bestValue;
336 sp->moveCount = moveCount;
341 assert(master->is_searching);
343 master->curSplitPoint = sp;
346 // Try to allocate available threads and ask them to start searching setting
347 // is_searching flag. This must be done under lock protection to avoid concurrent
348 // allocation of the same slave by another master.
350 lock_grab(splitLock);
352 for (int i = 0; i < size() && !Fake; ++i)
353 if (threads[i]->is_available_to(master))
355 sp->slavesMask |= 1ULL << i;
356 threads[i]->curSplitPoint = sp;
357 threads[i]->is_searching = true; // Slave leaves idle_loop()
359 if (useSleepingThreads)
360 threads[i]->wake_up();
362 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
366 lock_release(splitLock);
367 lock_release(sp->lock);
369 // Everything is set up. The master thread enters the idle loop, from which
370 // it will instantly launch a search, because its is_searching flag is set.
371 // We pass the split point as a parameter to the idle loop, which means that
372 // the thread will return from the idle loop when all slaves have finished
373 // their work at this split point.
374 if (slavesCnt || Fake)
376 master->idle_loop(sp);
378 // In helpful master concept a master can help only a sub-tree of its split
379 // point, and because here is all finished is not possible master is booked.
380 assert(!master->is_searching);
383 // We have returned from the idle loop, which means that all threads are
384 // finished. Note that setting is_searching and decreasing splitPointsCnt is
385 // done under lock protection to avoid a race with Thread::is_available_to().
386 lock_grab(sp->lock); // To protect sp->nodes
387 lock_grab(splitLock);
389 master->is_searching = true;
390 master->splitPointsCnt--;
391 master->curSplitPoint = sp->parent;
392 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
393 *bestMove = sp->bestMove;
395 lock_release(splitLock);
396 lock_release(sp->lock);
398 return sp->bestValue;
401 // Explicit template instantiations
402 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
403 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
406 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
407 // milliseconds. If msec is 0 then timer is stopped.
409 void ThreadsManager::set_timer(int msec) {
411 lock_grab(timer->sleepLock);
412 timer->maxPly = msec;
413 cond_signal(timer->sleepCond); // Wake up and restart the timer
414 lock_release(timer->sleepLock);
418 // ThreadsManager::wait_for_search_finished() waits for main thread to go to
419 // sleep, this means search is finished. Then returns.
421 void ThreadsManager::wait_for_search_finished() {
423 Thread* t = main_thread();
424 lock_grab(t->sleepLock);
425 cond_signal(t->sleepCond); // In case is waiting for stop or ponderhit
426 while (!t->do_sleep) cond_wait(sleepCond, t->sleepLock);
427 lock_release(t->sleepLock);
431 // ThreadsManager::start_searching() wakes up the main thread sleeping in
432 // main_loop() so to start a new search, then returns immediately.
434 void ThreadsManager::start_searching(const Position& pos, const LimitsType& limits,
435 const std::vector<Move>& searchMoves) {
436 wait_for_search_finished();
438 SearchTime.restart(); // As early as possible
440 Signals.stopOnPonderhit = Signals.firstRootMove = false;
441 Signals.stop = Signals.failedLowAtRoot = false;
447 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
448 if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
449 RootMoves.push_back(RootMove(ml.move()));
451 main_thread()->do_sleep = false;
452 main_thread()->wake_up();