2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <algorithm> // For std::count
28 #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::bestMoveCount(Move move) return best move counter for the given root move
58 int Thread::best_move_count(Move move) const {
60 auto rm = std::find(rootMoves.begin() + pvIdx,
61 rootMoves.begin() + pvLast, move);
63 return rm != rootMoves.begin() + pvLast ? rm->bestMoveCount : 0;
67 /// Thread::clear() reset histories, usually before a new game
69 void Thread::clear() {
71 counterMoves.fill(MOVE_NONE);
73 lowPlyHistory.fill(0);
74 captureHistory.fill(0);
76 for (bool inCheck : { false, true })
77 for (StatsType c : { NoCaptures, Captures })
79 for (auto& to : continuationHistory[inCheck][c])
82 continuationHistory[inCheck][c][NO_PIECE][0]->fill(Search::CounterMovePruneThreshold - 1);
87 /// Thread::start_searching() wakes up the thread that will start the search
89 void Thread::start_searching() {
91 std::lock_guard<std::mutex> lk(mutex);
93 cv.notify_one(); // Wake up the thread in idle_loop()
97 /// Thread::wait_for_search_finished() blocks on the condition variable
98 /// until the thread has finished searching.
100 void Thread::wait_for_search_finished() {
102 std::unique_lock<std::mutex> lk(mutex);
103 cv.wait(lk, [&]{ return !searching; });
107 /// Thread::idle_loop() is where the thread is parked, blocked on the
108 /// condition variable, when it has no work to do.
110 void Thread::idle_loop() {
112 // If OS already scheduled us on a different group than 0 then don't overwrite
113 // the choice, eventually we are one of many one-threaded processes running on
114 // some Windows NUMA hardware, for instance in fishtest. To make it simple,
115 // just check if running threads are below a threshold, in this case all this
116 // NUMA machinery is not needed.
117 if (Options["Threads"] > 8)
118 WinProcGroup::bindThisThread(idx);
122 std::unique_lock<std::mutex> lk(mutex);
124 cv.notify_one(); // Wake up anyone waiting for search finished
125 cv.wait(lk, [&]{ return searching; });
136 /// ThreadPool::set() creates/destroys threads to match the requested number.
137 /// Created and launched threads will immediately go to sleep in idle_loop.
138 /// Upon resizing, threads are recreated to allow for binding if necessary.
140 void ThreadPool::set(size_t requested) {
142 if (size() > 0) { // destroy any existing thread(s)
143 main()->wait_for_search_finished();
146 delete back(), pop_back();
149 if (requested > 0) { // create new thread(s)
150 push_back(new MainThread(0));
152 while (size() < requested)
153 push_back(new Thread(size()));
156 // Reallocate the hash with the new threadpool size
157 TT.resize(size_t(Options["Hash"]));
159 // Init thread number dependent search params.
165 /// ThreadPool::clear() sets threadPool data to initial values
167 void ThreadPool::clear() {
169 for (Thread* th : *this)
172 main()->callsCnt = 0;
173 main()->bestPreviousScore = VALUE_INFINITE;
174 main()->previousTimeReduction = 1.0;
178 /// ThreadPool::start_thinking() wakes up main thread waiting in idle_loop() and
179 /// returns immediately. Main thread will wake up other threads and start the search.
181 void ThreadPool::start_thinking(Position& pos, StateListPtr& states,
182 const Search::LimitsType& limits, bool ponderMode) {
184 main()->wait_for_search_finished();
186 main()->stopOnPonderhit = stop = false;
187 increaseDepth = true;
188 main()->ponder = ponderMode;
189 Search::Limits = limits;
190 Search::RootMoves rootMoves;
192 for (const auto& m : MoveList<LEGAL>(pos))
193 if ( limits.searchmoves.empty()
194 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
195 rootMoves.emplace_back(m);
197 if (!rootMoves.empty())
198 Tablebases::rank_root_moves(pos, rootMoves);
200 // After ownership transfer 'states' becomes empty, so if we stop the search
201 // and call 'go' again without setting a new position states.get() == NULL.
202 assert(states.get() || setupStates.get());
205 setupStates = std::move(states); // Ownership transfer, states is now empty
207 // We use Position::set() to set root position across threads. But there are
208 // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
209 // be deduced from a fen string, so set() clears them and to not lose the info
210 // we need to backup and later restore setupStates->back(). Note that setupStates
211 // is shared by threads but is accessed in read-only mode.
212 StateInfo tmp = setupStates->back();
214 for (Thread* th : *this)
216 th->nodes = th->tbHits = th->nmpMinPly = th->bestMoveChanges = 0;
217 th->rootDepth = th->completedDepth = 0;
218 th->rootMoves = rootMoves;
219 th->rootPos.set(pos.fen(), pos.is_chess960(), &setupStates->back(), th);
222 setupStates->back() = tmp;
224 main()->start_searching();
227 Thread* ThreadPool::get_best_thread() const {
229 Thread* bestThread = front();
230 std::map<Move, int64_t> votes;
231 Value minScore = VALUE_NONE;
233 // Find minimum score of all threads
234 for (Thread* th: *this)
235 minScore = std::min(minScore, th->rootMoves[0].score);
237 // Vote according to score and depth, and select the best thread
238 for (Thread* th : *this)
240 votes[th->rootMoves[0].pv[0]] +=
241 (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
243 if (abs(bestThread->rootMoves[0].score) >= VALUE_TB_WIN_IN_MAX_PLY)
245 // Make sure we pick the shortest mate / TB conversion or stave off mate the longest
246 if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
249 else if ( th->rootMoves[0].score >= VALUE_TB_WIN_IN_MAX_PLY
250 || ( th->rootMoves[0].score > VALUE_TB_LOSS_IN_MAX_PLY
251 && votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]))
259 /// Start non-main threads
261 void ThreadPool::start_searching() {
263 for (Thread* th : *this)
265 th->start_searching();
269 /// Wait for non-main threads
271 void ThreadPool::wait_for_search_finished() const {
273 for (Thread* th : *this)
275 th->wait_for_search_finished();