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) : splitPoints() {
47 is_searching = do_exit = false;
48 maxPly = splitPointsCnt = 0;
54 if (!thread_create(handle, start_routine, this))
56 std::cerr << "Failed to create thread number " << idx << std::endl;
62 // Thread d'tor waits for thread termination before to return.
68 do_exit = true; // Search must be already finished
70 thread_join(handle); // Wait for thread termination
74 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
75 // then calls check_time(). If maxPly is 0 thread sleeps until is woken up.
76 extern void check_time();
78 void Thread::timer_loop() {
83 while (!maxPly && !do_exit)
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);
118 assert(is_searching);
123 // Thread::notify_one() wakes up the thread, normally at the beginning of the
124 // search or, if "sleeping threads" is used at split time.
126 void Thread::notify_one() {
129 sleepCondition.notify_one();
134 // Thread::wait_for() set the thread to sleep until condition 'b' turns true
136 void Thread::wait_for(volatile const bool& b) {
139 while (!b) sleepCondition.wait(mutex);
144 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
145 // current active split point, or in some ancestor of the split point.
147 bool Thread::cutoff_occurred() const {
149 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
157 // Thread::is_available_to() checks whether the thread is available to help the
158 // thread 'master' at a split point. An obvious requirement is that thread must
159 // be idle. With more than two threads, this is not sufficient: If the thread is
160 // the master of some active split point, it is only available as a slave to the
161 // slaves which are busy searching the split point at the top of slaves split
162 // point stack (the "helpful master concept" in YBWC terminology).
164 bool Thread::is_available_to(Thread* master) const {
169 // Make a local copy to be sure doesn't become zero under our feet while
170 // testing next condition and so leading to an out of bound access.
171 int spCnt = splitPointsCnt;
173 // No active split points means that the thread is available as a slave for any
174 // other thread otherwise apply the "helpful master" concept if possible.
175 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master->idx));
179 // init() is called at startup. Initializes lock and condition variable and
180 // launches requested threads sending them immediately to sleep. We cannot use
181 // a c'tor becuase Threads is a static object and we need a fully initialized
182 // engine at this point due to allocation of endgames in Thread c'tor.
184 void ThreadPool::init() {
186 timer = new Thread(&Thread::timer_loop);
187 threads.push_back(new Thread(&Thread::main_loop));
192 // exit() cleanly terminates the threads before the program exits.
194 void ThreadPool::exit() {
196 delete timer; // As first becuase check_time() accesses threads data
198 for (size_t i = 0; i < threads.size(); i++)
203 // read_uci_options() updates internal threads parameters from the corresponding
204 // UCI options and creates/destroys threads to match the requested number. Thread
205 // objects are dynamically allocated to avoid creating in advance all possible
206 // threads, with included pawns and material tables, if only few are used.
208 void ThreadPool::read_uci_options() {
210 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
211 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
212 useSleepingThreads = Options["Use Sleeping Threads"];
213 size_t requested = Options["Threads"];
215 assert(requested > 0);
217 while (threads.size() < requested)
218 threads.push_back(new Thread(&Thread::idle_loop));
220 while (threads.size() > requested)
222 delete threads.back();
228 // available_slave_exists() tries to find an idle thread which is available as
229 // a slave for the thread 'master'.
231 bool ThreadPool::available_slave_exists(Thread* master) const {
233 for (size_t i = 0; i < threads.size(); i++)
234 if (threads[i]->is_available_to(master))
241 // split() does the actual work of distributing the work at a node between
242 // several available threads. If it does not succeed in splitting the node
243 // (because no idle threads are available, or because we have no unused split
244 // point objects), the function immediately returns. If splitting is possible, a
245 // SplitPoint object is initialized with all the data that must be copied to the
246 // helper threads and then helper threads are told that they have been assigned
247 // work. This will cause them to instantly leave their idle loops and call
248 // search(). When all threads have returned from search() then split() returns.
251 Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
252 Value bestValue, Move* bestMove, Depth depth, Move threatMove,
253 int moveCount, MovePicker& mp, int nodeType) {
255 assert(pos.pos_is_ok());
256 assert(bestValue > -VALUE_INFINITE);
257 assert(bestValue <= alpha);
258 assert(alpha < beta);
259 assert(beta <= VALUE_INFINITE);
260 assert(depth > DEPTH_ZERO);
262 Thread* master = pos.this_thread();
264 if (master->splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
267 // Pick the next available split point from the split point stack
268 SplitPoint& sp = master->splitPoints[master->splitPointsCnt];
270 sp.parent = master->curSplitPoint;
273 sp.slavesMask = 1ULL << master->idx;
275 sp.bestMove = *bestMove;
276 sp.threatMove = threatMove;
279 sp.nodeType = nodeType;
280 sp.bestValue = bestValue;
282 sp.moveCount = moveCount;
287 assert(master->is_searching);
289 master->curSplitPoint = &sp;
292 // Try to allocate available threads and ask them to start searching setting
293 // is_searching flag. This must be done under lock protection to avoid concurrent
294 // allocation of the same slave by another master.
298 for (size_t i = 0; i < threads.size() && !Fake; ++i)
299 if (threads[i]->is_available_to(master))
301 sp.slavesMask |= 1ULL << i;
302 threads[i]->curSplitPoint = &sp;
303 threads[i]->is_searching = true; // Slave leaves idle_loop()
305 if (useSleepingThreads)
306 threads[i]->notify_one();
308 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
312 master->splitPointsCnt++;
317 // Everything is set up. The master thread enters the idle loop, from which
318 // it will instantly launch a search, because its is_searching flag is set.
319 // The thread will return from the idle loop when all slaves have finished
320 // their work at this split point.
321 if (slavesCnt || Fake)
325 // In helpful master concept a master can help only a sub-tree of its split
326 // point, and because here is all finished is not possible master is booked.
327 assert(!master->is_searching);
330 // We have returned from the idle loop, which means that all threads are
331 // finished. Note that setting is_searching and decreasing splitPointsCnt is
332 // done under lock protection to avoid a race with Thread::is_available_to().
336 master->is_searching = true;
337 master->splitPointsCnt--;
338 master->curSplitPoint = sp.parent;
339 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
340 *bestMove = sp.bestMove;
348 // Explicit template instantiations
349 template Value ThreadPool::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
350 template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
353 // wait_for_search_finished() waits for main thread to go to sleep, this means
354 // search is finished. Then returns.
356 void ThreadPool::wait_for_search_finished() {
358 Thread* t = main_thread();
360 while (!t->do_sleep) sleepCondition.wait(t->mutex);
365 // start_searching() wakes up the main thread sleeping in main_loop() so to start
366 // a new search, then returns immediately.
368 void ThreadPool::start_searching(const Position& pos, const LimitsType& limits,
369 const std::vector<Move>& searchMoves, StateStackPtr& states) {
370 wait_for_search_finished();
372 SearchTime = Time::now(); // As early as possible
374 Signals.stopOnPonderhit = Signals.firstRootMove = false;
375 Signals.stop = Signals.failedLowAtRoot = false;
379 SetupStates = states; // Ownership transfer here
382 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
383 if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
384 RootMoves.push_back(RootMove(ml.move()));
386 main_thread()->do_sleep = false;
387 main_thread()->notify_one();