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 is a wrapper to member function pointed by start_fn.
37 long start_routine(Thread* th) { (th->*(th->start_fn))(); return 0; }
42 // Thread c'tor starts a newly-created thread of execution that will call
43 // the idle loop function pointed by start_fn going immediately to sleep.
45 Thread::Thread(Fn fn) {
47 is_searching = do_exit = false;
48 maxPly = splitPointsCnt = 0;
53 do_sleep = (fn != &Thread::main_loop); // Avoid a race with start_searching()
58 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
59 lock_init(splitPoints[j].lock);
61 if (!thread_create(handle, start_routine, this))
63 std::cerr << "Failed to create thread number " << idx << std::endl;
69 // Thread d'tor waits for thread termination before to return.
75 do_exit = true; // Search must be already finished
78 thread_join(handle); // Wait for thread termination
80 lock_destroy(sleepLock);
81 cond_destroy(sleepCond);
83 for (int j = 0; j < MAX_SPLITPOINTS_PER_THREAD; j++)
84 lock_destroy(splitPoints[j].lock);
88 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
89 // then calls check_time(). If maxPly is 0 thread sleeps until is woken up.
90 extern void check_time();
92 void Thread::timer_loop() {
97 timed_wait(sleepCond, sleepLock, maxPly ? maxPly : INT_MAX);
98 lock_release(sleepLock);
104 // Thread::main_loop() is where the main thread is parked waiting to be started
105 // when there is a new search. Main thread will launch all the slave threads.
107 void Thread::main_loop() {
111 lock_grab(sleepLock);
113 do_sleep = true; // Always return to sleep after a search
114 is_searching = false;
116 while (do_sleep && !do_exit)
118 cond_signal(Threads.sleepCond); // Wake up UI thread if needed
119 cond_wait(sleepCond, sleepLock);
122 lock_release(sleepLock);
134 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
135 // or, if "sleeping threads" is used at split time.
137 void Thread::wake_up() {
139 lock_grab(sleepLock);
140 cond_signal(sleepCond);
141 lock_release(sleepLock);
145 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
146 // reached while the program is pondering. The point is to work around a wrinkle
147 // in the UCI protocol: When pondering, the engine is not allowed to give a
148 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
149 // wait here until one of these commands (that raise StopRequest) is sent and
150 // then return, after which the bestmove and pondermove will be printed.
152 void Thread::wait_for_stop_or_ponderhit() {
154 Signals.stopOnPonderhit = true;
156 lock_grab(sleepLock);
157 while (!Signals.stop) cond_wait(sleepCond, sleepLock);
158 lock_release(sleepLock);
162 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
163 // current active split point, or in some ancestor of the split point.
165 bool Thread::cutoff_occurred() const {
167 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
175 // Thread::is_available_to() checks whether the thread is available to help the
176 // thread 'master' at a split point. An obvious requirement is that thread must
177 // be idle. With more than two threads, this is not sufficient: If the thread is
178 // the master of some active split point, it is only available as a slave to the
179 // slaves which are busy searching the split point at the top of slaves split
180 // point stack (the "helpful master concept" in YBWC terminology).
182 bool Thread::is_available_to(Thread* master) const {
187 // Make a local copy to be sure doesn't become zero under our feet while
188 // testing next condition and so leading to an out of bound access.
189 int spCnt = splitPointsCnt;
191 // No active split points means that the thread is available as a slave for any
192 // other thread otherwise apply the "helpful master" concept if possible.
193 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master->idx));
197 // init() is called at startup. Initializes lock and condition variable and
198 // launches requested threads sending them immediately to sleep. We cannot use
199 // a c'tor becuase Threads is a static object and we need a fully initialized
200 // engine at this point due to allocation of endgames in Thread c'tor.
202 void ThreadsManager::init() {
204 cond_init(sleepCond);
205 lock_init(splitLock);
206 timer = new Thread(&Thread::timer_loop);
207 threads.push_back(new Thread(&Thread::main_loop));
212 // d'tor cleanly terminates the threads when the program exits.
214 ThreadsManager::~ThreadsManager() {
216 for (int i = 0; i < size(); i++)
220 lock_destroy(splitLock);
221 cond_destroy(sleepCond);
225 // read_uci_options() updates internal threads parameters from the corresponding
226 // UCI options and creates/destroys threads to match the requested number. Thread
227 // objects are dynamically allocated to avoid creating in advance all possible
228 // threads, with included pawns and material tables, if only few are used.
230 void ThreadsManager::read_uci_options() {
232 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
233 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
234 useSleepingThreads = Options["Use Sleeping Threads"];
235 int requested = Options["Threads"];
237 assert(requested > 0);
239 while (size() < requested)
240 threads.push_back(new Thread(&Thread::idle_loop));
242 while (size() > requested)
244 delete threads.back();
250 // wake_up() is called before a new search to start the threads that are waiting
251 // on the sleep condition and to reset maxPly. When useSleepingThreads is set
252 // threads will be woken up at split time.
254 void ThreadsManager::wake_up() const {
256 for (int i = 0; i < size(); i++)
258 threads[i]->maxPly = 0;
259 threads[i]->do_sleep = false;
261 if (!useSleepingThreads)
262 threads[i]->wake_up();
267 // sleep() is called after the search finishes to ask all the threads but the
268 // main one to go waiting on a sleep condition.
270 void ThreadsManager::sleep() const {
272 for (int i = 1; i < size(); i++) // Main thread will go to sleep by itself
273 threads[i]->do_sleep = true; // to avoid a race with start_searching()
277 // available_slave_exists() tries to find an idle thread which is available as
278 // a slave for the thread 'master'.
280 bool ThreadsManager::available_slave_exists(Thread* master) const {
282 for (int i = 0; i < size(); i++)
283 if (threads[i]->is_available_to(master))
290 // split() does the actual work of distributing the work at a node between
291 // several available threads. If it does not succeed in splitting the node
292 // (because no idle threads are available, or because we have no unused split
293 // point objects), the function immediately returns. If splitting is possible, a
294 // SplitPoint object is initialized with all the data that must be copied to the
295 // helper threads and then helper threads are told that they have been assigned
296 // work. This will cause them to instantly leave their idle loops and call
297 // search(). When all threads have returned from search() then split() returns.
300 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
301 Value bestValue, Move* bestMove, Depth depth,
302 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
303 assert(pos.pos_is_ok());
304 assert(bestValue > -VALUE_INFINITE);
305 assert(bestValue <= alpha);
306 assert(alpha < beta);
307 assert(beta <= VALUE_INFINITE);
308 assert(depth > DEPTH_ZERO);
310 Thread* master = pos.this_thread();
312 if (master->splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
315 // Pick the next available split point from the split point stack
316 SplitPoint* sp = &master->splitPoints[master->splitPointsCnt];
318 sp->parent = master->curSplitPoint;
321 sp->slavesMask = 1ULL << master->idx;
322 sp->allSlavesRunning = true;
324 sp->bestMove = *bestMove;
325 sp->threatMove = threatMove;
328 sp->nodeType = nodeType;
329 sp->bestValue = bestValue;
331 sp->moveCount = moveCount;
336 assert(master->is_searching);
338 master->curSplitPoint = sp;
341 // Try to allocate available threads and ask them to start searching setting
342 // is_searching flag. This must be done under lock protection to avoid concurrent
343 // allocation of the same slave by another master.
345 lock_grab(splitLock);
347 for (int i = 0; i < size() && !Fake; ++i)
348 if (threads[i]->is_available_to(master))
350 sp->slavesMask |= 1ULL << i;
351 threads[i]->curSplitPoint = sp;
352 threads[i]->is_searching = true; // Slave leaves idle_loop()
354 if (useSleepingThreads)
355 threads[i]->wake_up();
357 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
361 master->splitPointsCnt++;
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)
373 master->idle_loop(sp);
375 // In helpful master concept a master can help only a sub-tree of its split
376 // point, and because here is all finished is not possible master is booked.
377 assert(!master->is_searching);
380 // We have returned from the idle loop, which means that all threads are
381 // finished. Note that setting is_searching and decreasing splitPointsCnt is
382 // done under lock protection to avoid a race with Thread::is_available_to().
383 lock_grab(sp->lock); // To protect sp->nodes
384 lock_grab(splitLock);
386 master->is_searching = true;
387 master->splitPointsCnt--;
388 master->curSplitPoint = sp->parent;
389 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
390 *bestMove = sp->bestMove;
392 lock_release(splitLock);
393 lock_release(sp->lock);
395 return sp->bestValue;
398 // Explicit template instantiations
399 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
400 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
403 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
404 // milliseconds. If msec is 0 then timer is stopped.
406 void ThreadsManager::set_timer(int msec) {
408 lock_grab(timer->sleepLock);
409 timer->maxPly = msec;
410 cond_signal(timer->sleepCond); // Wake up and restart the timer
411 lock_release(timer->sleepLock);
415 // ThreadsManager::wait_for_search_finished() waits for main thread to go to
416 // sleep, this means search is finished. Then returns.
418 void ThreadsManager::wait_for_search_finished() {
420 Thread* t = main_thread();
421 lock_grab(t->sleepLock);
422 cond_signal(t->sleepCond); // In case is waiting for stop or ponderhit
423 while (!t->do_sleep) cond_wait(sleepCond, t->sleepLock);
424 lock_release(t->sleepLock);
428 // ThreadsManager::start_searching() wakes up the main thread sleeping in
429 // main_loop() so to start a new search, then returns immediately.
431 void ThreadsManager::start_searching(const Position& pos, const LimitsType& limits,
432 const std::vector<Move>& searchMoves) {
433 wait_for_search_finished();
435 SearchTime.restart(); // As early as possible
437 Signals.stopOnPonderhit = Signals.firstRootMove = false;
438 Signals.stop = Signals.failedLowAtRoot = false;
444 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
445 if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
446 RootMoves.push_back(RootMove(ml.move()));
448 main_thread()->do_sleep = false;
449 main_thread()->wake_up();