2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2020 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"
29 ThreadPool Threads; // Global object
32 /// Thread constructor launches the thread and waits until it goes to sleep
33 /// in idle_loop(). Note that 'searching' and 'exit' should be already set.
35 Thread::Thread(size_t n) : idx(n), stdThread(&Thread::idle_loop, this) {
37 wait_for_search_finished();
41 /// Thread destructor wakes up the thread in idle_loop() and waits
42 /// for its termination. Thread should be already waiting.
54 /// Thread::bestMoveCount(Move move) return best move counter for the given root move
56 int Thread::best_move_count(Move move) const {
58 auto rm = std::find(rootMoves.begin() + pvIdx,
59 rootMoves.begin() + pvLast, move);
61 return rm != rootMoves.begin() + pvLast ? rm->bestMoveCount : 0;
65 /// Thread::clear() reset histories, usually before a new game
67 void Thread::clear() {
69 counterMoves.fill(MOVE_NONE);
71 lowPlyHistory.fill(0);
72 captureHistory.fill(0);
74 for (bool inCheck : { false, true })
75 for (StatsType c : { NoCaptures, Captures })
77 for (auto& to : continuationHistory[inCheck][c])
80 continuationHistory[inCheck][c][NO_PIECE][0]->fill(Search::CounterMovePruneThreshold - 1);
85 /// Thread::start_searching() wakes up the thread that will start the search
87 void Thread::start_searching() {
89 std::lock_guard<std::mutex> lk(mutex);
91 cv.notify_one(); // Wake up the thread in idle_loop()
95 /// Thread::wait_for_search_finished() blocks on the condition variable
96 /// until the thread has finished searching.
98 void Thread::wait_for_search_finished() {
100 std::unique_lock<std::mutex> lk(mutex);
101 cv.wait(lk, [&]{ return !searching; });
105 /// Thread::idle_loop() is where the thread is parked, blocked on the
106 /// condition variable, when it has no work to do.
108 void Thread::idle_loop() {
110 // If OS already scheduled us on a different group than 0 then don't overwrite
111 // the choice, eventually we are one of many one-threaded processes running on
112 // some Windows NUMA hardware, for instance in fishtest. To make it simple,
113 // just check if running threads are below a threshold, in this case all this
114 // NUMA machinery is not needed.
115 if (Options["Threads"] > 8)
116 WinProcGroup::bindThisThread(idx);
120 std::unique_lock<std::mutex> lk(mutex);
122 cv.notify_one(); // Wake up anyone waiting for search finished
123 cv.wait(lk, [&]{ return searching; });
134 /// ThreadPool::set() creates/destroys threads to match the requested number.
135 /// Created and launched threads will immediately go to sleep in idle_loop.
136 /// Upon resizing, threads are recreated to allow for binding if necessary.
138 void ThreadPool::set(size_t requested) {
140 if (size() > 0) { // destroy any existing thread(s)
141 main()->wait_for_search_finished();
144 delete back(), pop_back();
147 if (requested > 0) { // create new thread(s)
148 push_back(new MainThread(0));
150 while (size() < requested)
151 push_back(new Thread(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 : *this)
170 main()->callsCnt = 0;
171 main()->bestPreviousScore = VALUE_INFINITE;
172 main()->previousTimeReduction = 1.0;
176 /// ThreadPool::start_thinking() wakes up main thread waiting in idle_loop() and
177 /// returns immediately. Main thread will wake up other threads and start the search.
179 void ThreadPool::start_thinking(Position& pos, StateListPtr& states,
180 const Search::LimitsType& limits, bool ponderMode) {
182 main()->wait_for_search_finished();
184 main()->stopOnPonderhit = stop = false;
185 increaseDepth = true;
186 main()->ponder = ponderMode;
187 Search::Limits = limits;
188 Search::RootMoves rootMoves;
190 for (const auto& m : MoveList<LEGAL>(pos))
191 if ( limits.searchmoves.empty()
192 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
193 rootMoves.emplace_back(m);
195 if (!rootMoves.empty())
196 Tablebases::rank_root_moves(pos, rootMoves);
198 // After ownership transfer 'states' becomes empty, so if we stop the search
199 // and call 'go' again without setting a new position states.get() == NULL.
200 assert(states.get() || setupStates.get());
203 setupStates = std::move(states); // Ownership transfer, states is now empty
205 // We use Position::set() to set root position across threads. But there are
206 // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
207 // be deduced from a fen string, so set() clears them and to not lose the info
208 // we need to backup and later restore setupStates->back(). Note that setupStates
209 // is shared by threads but is accessed in read-only mode.
210 StateInfo tmp = setupStates->back();
212 for (Thread* th : *this)
214 th->nodes = th->tbHits = th->nmpMinPly = th->bestMoveChanges = 0;
215 th->rootDepth = th->completedDepth = 0;
216 th->rootMoves = rootMoves;
217 th->rootPos.set(pos.fen(), pos.is_chess960(), &setupStates->back(), th);
220 setupStates->back() = tmp;
222 main()->start_searching();
225 Thread* ThreadPool::get_best_thread() const {
227 Thread* bestThread = front();
228 std::map<Move, int64_t> votes;
229 Value minScore = VALUE_NONE;
231 // Find minimum score of all threads
232 for (Thread* th: *this)
233 minScore = std::min(minScore, th->rootMoves[0].score);
235 // Vote according to score and depth, and select the best thread
236 for (Thread* th : *this)
238 votes[th->rootMoves[0].pv[0]] +=
239 (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
241 if (abs(bestThread->rootMoves[0].score) >= VALUE_TB_WIN_IN_MAX_PLY)
243 // Make sure we pick the shortest mate / TB conversion or stave off mate the longest
244 if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
247 else if ( th->rootMoves[0].score >= VALUE_TB_WIN_IN_MAX_PLY
248 || ( th->rootMoves[0].score > VALUE_TB_LOSS_IN_MAX_PLY
249 && votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]))
257 /// Start non-main threads
259 void ThreadPool::start_searching() {
261 for (Thread* th : *this)
263 th->start_searching();
267 /// Wait for non-main threads
269 void ThreadPool::wait_for_search_finished() const {
271 for (Thread* th : *this)
273 th->wait_for_search_finished();