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 ThreadPool 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()
55 if (!thread_create(handle, start_routine, this))
57 std::cerr << "Failed to create thread number " << idx << std::endl;
63 // Thread d'tor waits for thread termination before to return.
69 do_exit = true; // Search must be already finished
71 thread_join(handle); // Wait for thread termination
75 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
76 // then calls check_time(). If maxPly is 0 thread sleeps until is woken up.
77 extern void check_time();
79 void Thread::timer_loop() {
84 sleepCondition.wait_for(mutex, maxPly ? maxPly : INT_MAX);
91 // Thread::main_loop() is where the main thread is parked waiting to be started
92 // when there is a new search. Main thread will launch all the slave threads.
94 void Thread::main_loop() {
100 do_sleep = true; // Always return to sleep after a search
101 is_searching = false;
103 while (do_sleep && !do_exit)
105 Threads.sleepCondition.notify_one(); // Wake up UI thread if needed
106 sleepCondition.wait(mutex);
121 // Thread::wake_up() wakes up the thread, normally at the beginning of the search
122 // or, if "sleeping threads" is used at split time.
124 void Thread::wake_up() {
127 sleepCondition.notify_one();
132 // Thread::wait_for_stop_or_ponderhit() is called when the maximum depth is
133 // reached while the program is pondering. The point is to work around a wrinkle
134 // in the UCI protocol: When pondering, the engine is not allowed to give a
135 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
136 // wait here until one of these commands (that raise StopRequest) is sent and
137 // then return, after which the bestmove and pondermove will be printed.
139 void Thread::wait_for_stop_or_ponderhit() {
141 Signals.stopOnPonderhit = true;
144 while (!Signals.stop) sleepCondition.wait(mutex);;
149 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
150 // current active split point, or in some ancestor of the split point.
152 bool Thread::cutoff_occurred() const {
154 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
162 // Thread::is_available_to() checks whether the thread is available to help the
163 // thread 'master' at a split point. An obvious requirement is that thread must
164 // be idle. With more than two threads, this is not sufficient: If the thread is
165 // the master of some active split point, it is only available as a slave to the
166 // slaves which are busy searching the split point at the top of slaves split
167 // point stack (the "helpful master concept" in YBWC terminology).
169 bool Thread::is_available_to(Thread* master) const {
174 // Make a local copy to be sure doesn't become zero under our feet while
175 // testing next condition and so leading to an out of bound access.
176 int spCnt = splitPointsCnt;
178 // No active split points means that the thread is available as a slave for any
179 // other thread otherwise apply the "helpful master" concept if possible.
180 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master->idx));
184 // init() is called at startup. Initializes lock and condition variable and
185 // launches requested threads sending them immediately to sleep. We cannot use
186 // a c'tor becuase Threads is a static object and we need a fully initialized
187 // engine at this point due to allocation of endgames in Thread c'tor.
189 void ThreadPool::init() {
191 timer = new Thread(&Thread::timer_loop);
192 threads.push_back(new Thread(&Thread::main_loop));
197 // d'tor cleanly terminates the threads when the program exits.
199 ThreadPool::~ThreadPool() {
201 for (size_t i = 0; i < size(); i++)
208 // read_uci_options() updates internal threads parameters from the corresponding
209 // UCI options and creates/destroys threads to match the requested number. Thread
210 // objects are dynamically allocated to avoid creating in advance all possible
211 // threads, with included pawns and material tables, if only few are used.
213 void ThreadPool::read_uci_options() {
215 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
216 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
217 useSleepingThreads = Options["Use Sleeping Threads"];
218 size_t requested = Options["Threads"];
220 assert(requested > 0);
222 while (size() < requested)
223 threads.push_back(new Thread(&Thread::idle_loop));
225 while (size() > requested)
227 delete threads.back();
233 // wake_up() is called before a new search to start the threads that are waiting
234 // on the sleep condition and to reset maxPly. When useSleepingThreads is set
235 // threads will be woken up at split time.
237 void ThreadPool::wake_up() const {
239 for (size_t i = 0; i < size(); i++)
241 threads[i]->maxPly = 0;
242 threads[i]->do_sleep = false;
244 if (!useSleepingThreads)
245 threads[i]->wake_up();
250 // sleep() is called after the search finishes to ask all the threads but the
251 // main one to go waiting on a sleep condition.
253 void ThreadPool::sleep() const {
255 for (size_t i = 1; i < size(); i++) // Main thread will go to sleep by itself
256 threads[i]->do_sleep = true; // to avoid a race with start_searching()
260 // available_slave_exists() tries to find an idle thread which is available as
261 // a slave for the thread 'master'.
263 bool ThreadPool::available_slave_exists(Thread* master) const {
265 for (size_t i = 0; i < size(); i++)
266 if (threads[i]->is_available_to(master))
273 // split() does the actual work of distributing the work at a node between
274 // several available threads. If it does not succeed in splitting the node
275 // (because no idle threads are available, or because we have no unused split
276 // point objects), the function immediately returns. If splitting is possible, a
277 // SplitPoint object is initialized with all the data that must be copied to the
278 // helper threads and then helper threads are told that they have been assigned
279 // work. This will cause them to instantly leave their idle loops and call
280 // search(). When all threads have returned from search() then split() returns.
283 Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
284 Value bestValue, Move* bestMove, Depth depth,
285 Move threatMove, int moveCount, MovePicker* mp, int nodeType) {
287 assert(pos.pos_is_ok());
288 assert(bestValue > -VALUE_INFINITE);
289 assert(bestValue <= alpha);
290 assert(alpha < beta);
291 assert(beta <= VALUE_INFINITE);
292 assert(depth > DEPTH_ZERO);
294 Thread* master = pos.this_thread();
296 if (master->splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
299 // Pick the next available split point from the split point stack
300 SplitPoint& sp = master->splitPoints[master->splitPointsCnt];
302 sp.parent = master->curSplitPoint;
305 sp.slavesMask = 1ULL << master->idx;
307 sp.bestMove = *bestMove;
308 sp.threatMove = threatMove;
311 sp.nodeType = nodeType;
312 sp.bestValue = bestValue;
314 sp.moveCount = moveCount;
319 assert(master->is_searching);
321 master->curSplitPoint = &sp;
324 // Try to allocate available threads and ask them to start searching setting
325 // is_searching flag. This must be done under lock protection to avoid concurrent
326 // allocation of the same slave by another master.
330 for (size_t i = 0; i < size() && !Fake; ++i)
331 if (threads[i]->is_available_to(master))
333 sp.slavesMask |= 1ULL << i;
334 threads[i]->curSplitPoint = &sp;
335 threads[i]->is_searching = true; // Slave leaves idle_loop()
337 if (useSleepingThreads)
338 threads[i]->wake_up();
340 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
344 master->splitPointsCnt++;
349 // Everything is set up. The master thread enters the idle loop, from which
350 // it will instantly launch a search, because its is_searching flag is set.
351 // The thread will return from the idle loop when all slaves have finished
352 // their work at this split point.
353 if (slavesCnt || Fake)
357 // In helpful master concept a master can help only a sub-tree of its split
358 // point, and because here is all finished is not possible master is booked.
359 assert(!master->is_searching);
362 // We have returned from the idle loop, which means that all threads are
363 // finished. Note that setting is_searching and decreasing splitPointsCnt is
364 // done under lock protection to avoid a race with Thread::is_available_to().
365 sp.mutex.lock(); // To protect sp.nodes
368 master->is_searching = true;
369 master->splitPointsCnt--;
370 master->curSplitPoint = sp.parent;
371 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
372 *bestMove = sp.bestMove;
380 // Explicit template instantiations
381 template Value ThreadPool::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
382 template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker*, int);
385 // set_timer() is used to set the timer to trigger after msec milliseconds.
386 // If msec is 0 then timer is stopped.
388 void ThreadPool::set_timer(int msec) {
391 timer->maxPly = msec;
392 timer->sleepCondition.notify_one(); // Wake up and restart the timer
393 timer->mutex.unlock();
397 // wait_for_search_finished() waits for main thread to go to sleep, this means
398 // search is finished. Then returns.
400 void ThreadPool::wait_for_search_finished() {
402 Thread* t = main_thread();
404 t->sleepCondition.notify_one(); // In case is waiting for stop or ponderhit
405 while (!t->do_sleep) sleepCondition.wait(t->mutex);
410 // start_searching() wakes up the main thread sleeping in main_loop() so to start
411 // a new search, then returns immediately.
413 void ThreadPool::start_searching(const Position& pos, const LimitsType& limits,
414 const std::vector<Move>& searchMoves) {
415 wait_for_search_finished();
417 SearchTime.restart(); // As early as possible
419 Signals.stopOnPonderhit = Signals.firstRootMove = false;
420 Signals.stop = Signals.failedLowAtRoot = false;
426 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
427 if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
428 RootMoves.push_back(RootMove(ml.move()));
430 main_thread()->do_sleep = false;
431 main_thread()->wake_up();