2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2022 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/>.
21 #include <algorithm> // For std::count
26 #include "syzygy/tbprobe.h"
31 ThreadPool Threads; // Global object
34 /// Thread constructor launches the thread and waits until it goes to sleep
35 /// in idle_loop(). Note that 'searching' and 'exit' should be already set.
37 Thread::Thread(size_t n) : idx(n), stdThread(&Thread::idle_loop, this) {
39 wait_for_search_finished();
43 /// Thread destructor wakes up the thread in idle_loop() and waits
44 /// for its termination. Thread should be already waiting.
56 /// Thread::clear() reset histories, usually before a new game
58 void Thread::clear() {
60 counterMoves.fill(MOVE_NONE);
62 captureHistory.fill(0);
65 for (bool inCheck : { false, true })
66 for (StatsType c : { NoCaptures, Captures })
67 for (auto& to : continuationHistory[inCheck][c])
73 /// Thread::start_searching() wakes up the thread that will start the search
75 void Thread::start_searching() {
77 std::lock_guard<std::mutex> lk(mutex);
79 cv.notify_one(); // Wake up the thread in idle_loop()
83 /// Thread::wait_for_search_finished() blocks on the condition variable
84 /// until the thread has finished searching.
86 void Thread::wait_for_search_finished() {
88 std::unique_lock<std::mutex> lk(mutex);
89 cv.wait(lk, [&]{ return !searching; });
93 /// Thread::idle_loop() is where the thread is parked, blocked on the
94 /// condition variable, when it has no work to do.
96 void Thread::idle_loop() {
98 // If OS already scheduled us on a different group than 0 then don't overwrite
99 // the choice, eventually we are one of many one-threaded processes running on
100 // some Windows NUMA hardware, for instance in fishtest. To make it simple,
101 // just check if running threads are below a threshold, in this case all this
102 // NUMA machinery is not needed.
103 if (Options["Threads"] > 8)
104 WinProcGroup::bindThisThread(idx);
108 std::unique_lock<std::mutex> lk(mutex);
110 cv.notify_one(); // Wake up anyone waiting for search finished
111 cv.wait(lk, [&]{ return searching; });
122 /// ThreadPool::set() creates/destroys threads to match the requested number.
123 /// Created and launched threads will immediately go to sleep in idle_loop.
124 /// Upon resizing, threads are recreated to allow for binding if necessary.
126 void ThreadPool::set(size_t requested) {
128 if (size() > 0) // destroy any existing thread(s)
130 main()->wait_for_search_finished();
133 delete back(), pop_back();
136 if (requested > 0) // create new thread(s)
138 push_back(new MainThread(0));
140 while (size() < requested)
141 push_back(new Thread(size()));
144 // Reallocate the hash with the new threadpool size
145 TT.resize(size_t(Options["Hash"]));
147 // Init thread number dependent search params.
153 /// ThreadPool::clear() sets threadPool data to initial values
155 void ThreadPool::clear() {
157 for (Thread* th : *this)
160 main()->callsCnt = 0;
161 main()->bestPreviousScore = VALUE_INFINITE;
162 main()->bestPreviousAverageScore = VALUE_INFINITE;
163 main()->previousTimeReduction = 1.0;
167 /// ThreadPool::start_thinking() wakes up main thread waiting in idle_loop() and
168 /// returns immediately. Main thread will wake up other threads and start the search.
170 void ThreadPool::start_thinking(Position& pos, StateListPtr& states,
171 const Search::LimitsType& limits, bool ponderMode) {
173 main()->wait_for_search_finished();
175 main()->stopOnPonderhit = stop = false;
176 increaseDepth = true;
177 main()->ponder = ponderMode;
178 Search::Limits = limits;
179 Search::RootMoves rootMoves;
181 for (const auto& m : MoveList<LEGAL>(pos))
182 if ( limits.searchmoves.empty()
183 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
184 rootMoves.emplace_back(m);
186 if (!rootMoves.empty())
187 Tablebases::rank_root_moves(pos, rootMoves);
189 // After ownership transfer 'states' becomes empty, so if we stop the search
190 // and call 'go' again without setting a new position states.get() == NULL.
191 assert(states.get() || setupStates.get());
194 setupStates = std::move(states); // Ownership transfer, states is now empty
196 // We use Position::set() to set root position across threads. But there are
197 // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
198 // be deduced from a fen string, so set() clears them and they are set from
199 // setupStates->back() later. The rootState is per thread, earlier states are shared
200 // since they are read-only.
201 for (Thread* th : *this)
203 th->nodes = th->tbHits = th->nmpMinPly = th->bestMoveChanges = 0;
204 th->rootDepth = th->completedDepth = 0;
205 th->rootMoves = rootMoves;
206 th->rootPos.set(pos.fen(), pos.is_chess960(), &th->rootState, th);
207 th->rootState = setupStates->back();
210 main()->start_searching();
213 Thread* ThreadPool::get_best_thread() const {
215 Thread* bestThread = front();
216 std::map<Move, int64_t> votes;
217 Value minScore = VALUE_NONE;
219 // Find minimum score of all threads
220 for (Thread* th: *this)
221 minScore = std::min(minScore, th->rootMoves[0].score);
223 // Vote according to score and depth, and select the best thread
224 for (Thread* th : *this)
226 votes[th->rootMoves[0].pv[0]] +=
227 (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
229 if (abs(bestThread->rootMoves[0].score) >= VALUE_TB_WIN_IN_MAX_PLY)
231 // Make sure we pick the shortest mate / TB conversion or stave off mate the longest
232 if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
235 else if ( th->rootMoves[0].score >= VALUE_TB_WIN_IN_MAX_PLY
236 || ( th->rootMoves[0].score > VALUE_TB_LOSS_IN_MAX_PLY
237 && ( votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]
238 || ( votes[th->rootMoves[0].pv[0]] == votes[bestThread->rootMoves[0].pv[0]]
239 && th->rootMoves[0].pv.size() > bestThread->rootMoves[0].pv.size()))))
247 /// Start non-main threads
249 void ThreadPool::start_searching() {
251 for (Thread* th : *this)
253 th->start_searching();
257 /// Wait for non-main threads
259 void ThreadPool::wait_for_search_finished() const {
261 for (Thread* th : *this)
263 th->wait_for_search_finished();
266 } // namespace Stockfish