2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2023 The Stockfish developers (see AUTHORS file)
5 Stockfish is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Stockfish is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
25 #include <initializer_list>
34 #include "syzygy/tbprobe.h"
40 ThreadPool Threads; // Global object
43 // Thread constructor launches the thread and waits until it goes to sleep
44 // in idle_loop(). Note that 'searching' and 'exit' should be already set.
46 Thread::Thread(size_t n) :
48 stdThread(&Thread::idle_loop, this) {
50 wait_for_search_finished();
54 // Thread destructor wakes up the thread in idle_loop() and waits
55 // for its termination. Thread should be already waiting.
67 // Thread::clear() reset histories, usually before a new game
69 void Thread::clear() {
71 counterMoves.fill(MOVE_NONE);
73 captureHistory.fill(0);
75 for (bool inCheck : {false, true})
76 for (StatsType c : {NoCaptures, Captures})
77 for (auto& to : continuationHistory[inCheck][c])
83 // Thread::start_searching() wakes up the thread that will start the search
85 void Thread::start_searching() {
88 mutex.unlock(); // Unlock before notifying saves a few CPU-cycles
89 cv.notify_one(); // Wake up the thread in idle_loop()
93 // Thread::wait_for_search_finished() blocks on the condition variable
94 // until the thread has finished searching.
96 void Thread::wait_for_search_finished() {
98 std::unique_lock<std::mutex> lk(mutex);
99 cv.wait(lk, [&] { return !searching; });
103 // Thread::idle_loop() is where the thread is parked, blocked on the
104 // condition variable, when it has no work to do.
106 void Thread::idle_loop() {
108 // If OS already scheduled us on a different group than 0 then don't overwrite
109 // the choice, eventually we are one of many one-threaded processes running on
110 // some Windows NUMA hardware, for instance in fishtest. To make it simple,
111 // just check if running threads are below a threshold, in this case, all this
112 // NUMA machinery is not needed.
113 if (Options["Threads"] > 8)
114 WinProcGroup::bindThisThread(idx);
118 std::unique_lock<std::mutex> lk(mutex);
120 cv.notify_one(); // Wake up anyone waiting for search finished
121 cv.wait(lk, [&] { return searching; });
132 // ThreadPool::set() creates/destroys threads to match the requested number.
133 // Created and launched threads will immediately go to sleep in idle_loop.
134 // Upon resizing, threads are recreated to allow for binding if necessary.
136 void ThreadPool::set(size_t requested) {
138 if (threads.size() > 0) // destroy any existing thread(s)
140 main()->wait_for_search_finished();
142 while (threads.size() > 0)
143 delete threads.back(), threads.pop_back();
146 if (requested > 0) // create new thread(s)
148 threads.push_back(new MainThread(0));
150 while (threads.size() < requested)
151 threads.push_back(new Thread(threads.size()));
154 // Reallocate the hash with the new threadpool size
155 TT.resize(size_t(Options["Hash"]));
157 // Init thread number dependent search params.
163 // ThreadPool::clear() sets threadPool data to initial values
165 void ThreadPool::clear() {
167 for (Thread* th : threads)
170 main()->callsCnt = 0;
171 main()->bestPreviousScore = VALUE_INFINITE;
172 main()->bestPreviousAverageScore = VALUE_INFINITE;
173 main()->previousTimeReduction = 1.0;
177 // ThreadPool::start_thinking() wakes up main thread waiting in idle_loop() and
178 // returns immediately. Main thread will wake up other threads and start the search.
180 void ThreadPool::start_thinking(Position& pos,
181 StateListPtr& states,
182 const Search::LimitsType& limits,
185 main()->wait_for_search_finished();
187 main()->stopOnPonderhit = stop = false;
188 increaseDepth = true;
189 main()->ponder = ponderMode;
190 Search::Limits = limits;
191 Search::RootMoves rootMoves;
193 for (const auto& m : MoveList<LEGAL>(pos))
194 if (limits.searchmoves.empty()
195 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
196 rootMoves.emplace_back(m);
198 if (!rootMoves.empty())
199 Tablebases::rank_root_moves(pos, rootMoves);
201 // After ownership transfer 'states' becomes empty, so if we stop the search
202 // and call 'go' again without setting a new position states.get() == nullptr.
203 assert(states.get() || setupStates.get());
206 setupStates = std::move(states); // Ownership transfer, states is now empty
208 // We use Position::set() to set root position across threads. But there are
209 // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
210 // be deduced from a fen string, so set() clears them and they are set from
211 // setupStates->back() later. The rootState is per thread, earlier states are shared
212 // since they are read-only.
213 for (Thread* th : threads)
215 th->nodes = th->tbHits = th->nmpMinPly = th->bestMoveChanges = 0;
216 th->rootDepth = th->completedDepth = 0;
217 th->rootMoves = rootMoves;
218 th->rootPos.set(pos.fen(), pos.is_chess960(), &th->rootState, th);
219 th->rootState = setupStates->back();
220 th->rootSimpleEval = Eval::simple_eval(pos, pos.side_to_move());
223 main()->start_searching();
226 Thread* ThreadPool::get_best_thread() const {
228 Thread* bestThread = threads.front();
229 std::map<Move, int64_t> votes;
230 Value minScore = VALUE_NONE;
232 // Find the minimum score of all threads
233 for (Thread* th : threads)
234 minScore = std::min(minScore, th->rootMoves[0].score);
236 // Vote according to score and depth, and select the best thread
237 auto thread_value = [minScore](Thread* th) {
238 return (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
241 for (Thread* th : threads)
242 votes[th->rootMoves[0].pv[0]] += thread_value(th);
244 for (Thread* th : threads)
245 if (abs(bestThread->rootMoves[0].score) >= VALUE_TB_WIN_IN_MAX_PLY)
247 // Make sure we pick the shortest mate / TB conversion or stave off mate the longest
248 if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
251 else if (th->rootMoves[0].score >= VALUE_TB_WIN_IN_MAX_PLY
252 || (th->rootMoves[0].score > VALUE_TB_LOSS_IN_MAX_PLY
253 && (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]
254 || (votes[th->rootMoves[0].pv[0]] == votes[bestThread->rootMoves[0].pv[0]]
255 && thread_value(th) * int(th->rootMoves[0].pv.size() > 2)
256 > thread_value(bestThread)
257 * int(bestThread->rootMoves[0].pv.size() > 2)))))
264 // Start non-main threads
266 void ThreadPool::start_searching() {
268 for (Thread* th : threads)
269 if (th != threads.front())
270 th->start_searching();
274 // Wait for non-main threads
276 void ThreadPool::wait_for_search_finished() const {
278 for (Thread* th : threads)
279 if (th != threads.front())
280 th->wait_for_search_finished();
283 } // namespace Stockfish