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 // Constructor launches the thread and waits until it goes to sleep
44 // in idle_loop(). Note that 'searching' and 'exit' should be already set.
45 Thread::Thread(size_t n) :
47 stdThread(&Thread::idle_loop, this) {
49 wait_for_search_finished();
53 // Destructor wakes up the thread in idle_loop() and waits
54 // for its termination. Thread should be already waiting.
65 // Reset histories, usually before a new game
66 void Thread::clear() {
68 counterMoves.fill(MOVE_NONE);
70 captureHistory.fill(0);
73 for (bool inCheck : {false, true})
74 for (StatsType c : {NoCaptures, Captures})
75 for (auto& to : continuationHistory[inCheck][c])
81 // Wakes up the thread that will start the search
82 void Thread::start_searching() {
85 mutex.unlock(); // Unlock before notifying saves a few CPU-cycles
86 cv.notify_one(); // Wake up the thread in idle_loop()
90 // Blocks on the condition variable
91 // until the thread has finished searching.
92 void Thread::wait_for_search_finished() {
94 std::unique_lock<std::mutex> lk(mutex);
95 cv.wait(lk, [&] { return !searching; });
99 // Thread gets parked here, blocked on the
100 // condition variable, when it has no work to do.
102 void Thread::idle_loop() {
104 // If OS already scheduled us on a different group than 0 then don't overwrite
105 // the choice, eventually we are one of many one-threaded processes running on
106 // some Windows NUMA hardware, for instance in fishtest. To make it simple,
107 // just check if running threads are below a threshold, in this case, all this
108 // NUMA machinery is not needed.
109 if (Options["Threads"] > 8)
110 WinProcGroup::bindThisThread(idx);
114 std::unique_lock<std::mutex> lk(mutex);
116 cv.notify_one(); // Wake up anyone waiting for search finished
117 cv.wait(lk, [&] { return searching; });
128 // Creates/destroys threads to match the requested number.
129 // Created and launched threads will immediately go to sleep in idle_loop.
130 // Upon resizing, threads are recreated to allow for binding if necessary.
131 void ThreadPool::set(size_t requested) {
133 if (threads.size() > 0) // destroy any existing thread(s)
135 main()->wait_for_search_finished();
137 while (threads.size() > 0)
138 delete threads.back(), threads.pop_back();
141 if (requested > 0) // create new thread(s)
143 threads.push_back(new MainThread(0));
145 while (threads.size() < requested)
146 threads.push_back(new Thread(threads.size()));
149 // Reallocate the hash with the new threadpool size
150 TT.resize(size_t(Options["Hash"]));
152 // Init thread number dependent search params.
158 // Sets threadPool data to initial values
159 void ThreadPool::clear() {
161 for (Thread* th : threads)
164 main()->callsCnt = 0;
165 main()->bestPreviousScore = VALUE_INFINITE;
166 main()->bestPreviousAverageScore = VALUE_INFINITE;
167 main()->previousTimeReduction = 1.0;
171 // Wakes up main thread waiting in idle_loop() and
172 // returns immediately. Main thread will wake up other threads and start the search.
173 void ThreadPool::start_thinking(Position& pos,
174 StateListPtr& states,
175 const Search::LimitsType& limits,
178 main()->wait_for_search_finished();
180 main()->stopOnPonderhit = stop = false;
181 increaseDepth = true;
182 main()->ponder = ponderMode;
183 Search::Limits = limits;
184 Search::RootMoves rootMoves;
186 for (const auto& m : MoveList<LEGAL>(pos))
187 if (limits.searchmoves.empty()
188 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
189 rootMoves.emplace_back(m);
191 if (!rootMoves.empty())
192 Tablebases::rank_root_moves(pos, rootMoves);
194 // After ownership transfer 'states' becomes empty, so if we stop the search
195 // and call 'go' again without setting a new position states.get() == nullptr.
196 assert(states.get() || setupStates.get());
199 setupStates = std::move(states); // Ownership transfer, states is now empty
201 // We use Position::set() to set root position across threads. But there are
202 // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
203 // be deduced from a fen string, so set() clears them and they are set from
204 // setupStates->back() later. The rootState is per thread, earlier states are shared
205 // since they are read-only.
206 for (Thread* th : threads)
208 th->nodes = th->tbHits = th->nmpMinPly = th->bestMoveChanges = 0;
209 th->rootDepth = th->completedDepth = 0;
210 th->rootMoves = rootMoves;
211 th->rootPos.set(pos.fen(), pos.is_chess960(), &th->rootState, th);
212 th->rootState = setupStates->back();
213 th->rootSimpleEval = Eval::simple_eval(pos, pos.side_to_move());
216 main()->start_searching();
219 Thread* ThreadPool::get_best_thread() const {
221 Thread* bestThread = threads.front();
222 std::map<Move, int64_t> votes;
223 Value minScore = VALUE_NONE;
225 // Find the minimum score of all threads
226 for (Thread* th : threads)
227 minScore = std::min(minScore, th->rootMoves[0].score);
229 // Vote according to score and depth, and select the best thread
230 auto thread_value = [minScore](Thread* th) {
231 return (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
234 for (Thread* th : threads)
235 votes[th->rootMoves[0].pv[0]] += thread_value(th);
237 for (Thread* th : threads)
238 if (abs(bestThread->rootMoves[0].score) >= VALUE_TB_WIN_IN_MAX_PLY)
240 // Make sure we pick the shortest mate / TB conversion or stave off mate the longest
241 if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
244 else if (th->rootMoves[0].score >= VALUE_TB_WIN_IN_MAX_PLY
245 || (th->rootMoves[0].score > VALUE_TB_LOSS_IN_MAX_PLY
246 && (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]
247 || (votes[th->rootMoves[0].pv[0]] == votes[bestThread->rootMoves[0].pv[0]]
248 && thread_value(th) * int(th->rootMoves[0].pv.size() > 2)
249 > thread_value(bestThread)
250 * int(bestThread->rootMoves[0].pv.size() > 2)))))
257 // Start non-main threads
259 void ThreadPool::start_searching() {
261 for (Thread* th : threads)
262 if (th != threads.front())
263 th->start_searching();
267 // Wait for non-main threads
269 void ThreadPool::wait_for_search_finished() const {
271 for (Thread* th : threads)
272 if (th != threads.front())
273 th->wait_for_search_finished();
276 } // namespace Stockfish