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/>.
26 #include <initializer_list>
35 #include "syzygy/tbprobe.h"
41 ThreadPool Threads; // Global object
44 // Constructor launches the thread and waits until it goes to sleep
45 // 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 // Destructor wakes up the thread in idle_loop() and waits
55 // for its termination. Thread should be already waiting.
66 // Reset histories, usually before a new game
67 void Thread::clear() {
69 counterMoves.fill(MOVE_NONE);
71 captureHistory.fill(0);
74 for (bool inCheck : {false, true})
75 for (StatsType c : {NoCaptures, Captures})
76 for (auto& to : continuationHistory[inCheck][c])
82 // Wakes up the thread that will start the search
83 void Thread::start_searching() {
86 mutex.unlock(); // Unlock before notifying saves a few CPU-cycles
87 cv.notify_one(); // Wake up the thread in idle_loop()
91 // Blocks on the condition variable
92 // until the thread has finished searching.
93 void Thread::wait_for_search_finished() {
95 std::unique_lock<std::mutex> lk(mutex);
96 cv.wait(lk, [&] { return !searching; });
100 // Thread gets parked here, blocked on the
101 // condition variable, when it has no work to do.
103 void Thread::idle_loop() {
105 // If OS already scheduled us on a different group than 0 then don't overwrite
106 // the choice, eventually we are one of many one-threaded processes running on
107 // some Windows NUMA hardware, for instance in fishtest. To make it simple,
108 // just check if running threads are below a threshold, in this case, all this
109 // NUMA machinery is not needed.
110 if (Options["Threads"] > 8)
111 WinProcGroup::bindThisThread(idx);
115 std::unique_lock<std::mutex> lk(mutex);
117 cv.notify_one(); // Wake up anyone waiting for search finished
118 cv.wait(lk, [&] { return searching; });
129 // Creates/destroys threads to match the requested number.
130 // Created and launched threads will immediately go to sleep in idle_loop.
131 // Upon resizing, threads are recreated to allow for binding if necessary.
132 void ThreadPool::set(size_t requested) {
134 if (threads.size() > 0) // destroy any existing thread(s)
136 main()->wait_for_search_finished();
138 while (threads.size() > 0)
139 delete threads.back(), threads.pop_back();
142 if (requested > 0) // create new thread(s)
144 threads.push_back(new MainThread(0));
146 while (threads.size() < requested)
147 threads.push_back(new Thread(threads.size()));
150 // Reallocate the hash with the new threadpool size
151 TT.resize(size_t(Options["Hash"]));
153 // Init thread number dependent search params.
159 // Sets threadPool data to initial values
160 void ThreadPool::clear() {
162 for (Thread* th : threads)
165 main()->callsCnt = 0;
166 main()->bestPreviousScore = VALUE_INFINITE;
167 main()->bestPreviousAverageScore = VALUE_INFINITE;
168 main()->previousTimeReduction = 1.0;
172 // Wakes up main thread waiting in idle_loop() and
173 // returns immediately. Main thread will wake up other threads and start the search.
174 void ThreadPool::start_thinking(Position& pos,
175 StateListPtr& states,
176 const Search::LimitsType& limits,
179 main()->wait_for_search_finished();
181 main()->stopOnPonderhit = stop = false;
182 increaseDepth = true;
183 main()->ponder = ponderMode;
184 Search::Limits = limits;
185 Search::RootMoves rootMoves;
187 for (const auto& m : MoveList<LEGAL>(pos))
188 if (limits.searchmoves.empty()
189 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
190 rootMoves.emplace_back(m);
192 if (!rootMoves.empty())
193 Tablebases::rank_root_moves(pos, rootMoves);
195 // After ownership transfer 'states' becomes empty, so if we stop the search
196 // and call 'go' again without setting a new position states.get() == nullptr.
197 assert(states.get() || setupStates.get());
200 setupStates = std::move(states); // Ownership transfer, states is now empty
202 // We use Position::set() to set root position across threads. But there are
203 // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
204 // be deduced from a fen string, so set() clears them and they are set from
205 // setupStates->back() later. The rootState is per thread, earlier states are shared
206 // since they are read-only.
207 for (Thread* th : threads)
209 th->nodes = th->tbHits = th->nmpMinPly = th->bestMoveChanges = 0;
210 th->rootDepth = th->completedDepth = 0;
211 th->rootMoves = rootMoves;
212 th->rootPos.set(pos.fen(), pos.is_chess960(), &th->rootState, th);
213 th->rootState = setupStates->back();
214 th->rootSimpleEval = Eval::simple_eval(pos, pos.side_to_move());
217 main()->start_searching();
220 Thread* ThreadPool::get_best_thread() const {
222 Thread* bestThread = threads.front();
223 std::map<Move, int64_t> votes;
224 Value minScore = VALUE_NONE;
226 // Find the minimum score of all threads
227 for (Thread* th : threads)
228 minScore = std::min(minScore, th->rootMoves[0].score);
230 // Vote according to score and depth, and select the best thread
231 auto thread_value = [minScore](Thread* th) {
232 return (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
235 for (Thread* th : threads)
236 votes[th->rootMoves[0].pv[0]] += thread_value(th);
238 for (Thread* th : threads)
239 if (std::abs(bestThread->rootMoves[0].score) >= VALUE_TB_WIN_IN_MAX_PLY)
241 // Make sure we pick the shortest mate / TB conversion or stave off mate the longest
242 if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
245 else if (th->rootMoves[0].score >= VALUE_TB_WIN_IN_MAX_PLY
246 || (th->rootMoves[0].score > VALUE_TB_LOSS_IN_MAX_PLY
247 && (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]
248 || (votes[th->rootMoves[0].pv[0]] == votes[bestThread->rootMoves[0].pv[0]]
249 && thread_value(th) * int(th->rootMoves[0].pv.size() > 2)
250 > thread_value(bestThread)
251 * int(bestThread->rootMoves[0].pv.size() > 2)))))
258 // Start non-main threads
260 void ThreadPool::start_searching() {
262 for (Thread* th : threads)
263 if (th != threads.front())
264 th->start_searching();
268 // Wait for non-main threads
270 void ThreadPool::wait_for_search_finished() const {
272 for (Thread* th : threads)
273 if (th != threads.front())
274 th->wait_for_search_finished();
277 } // namespace Stockfish