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
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
20 #include <algorithm> // For std::count
28 using namespace Search;
30 ThreadPool Threads; // Global object
32 extern void check_time();
36 // Helpers to launch a thread after creation and joining before delete. Must be
37 // outside Thread c'tor and d'tor because the object must be fully initialized
38 // when start_routine (and hence virtual idle_loop) is called and when joining.
40 template<typename T> T* new_thread() {
42 th->nativeThread = std::thread(&ThreadBase::idle_loop, th); // Will go to sleep
46 void delete_thread(ThreadBase* th) {
49 th->exit = true; // Search must be already finished
53 th->nativeThread.join(); // Wait for thread termination
60 // ThreadBase::notify_one() wakes up the thread when there is some work to do
62 void ThreadBase::notify_one() {
64 std::unique_lock<std::mutex>(this->mutex);
65 sleepCondition.notify_one();
69 // ThreadBase::wait_for() set the thread to sleep until 'condition' turns true
71 void ThreadBase::wait_for(volatile const bool& condition) {
73 std::unique_lock<std::mutex> lk(mutex);
74 sleepCondition.wait(lk, [&]{ return condition; });
78 // Thread c'tor makes some init but does not launch any execution thread that
79 // will be started only when c'tor returns.
81 Thread::Thread() /* : splitPoints() */ { // Initialization of non POD broken in MSVC
86 activeSplitPoint = nullptr;
87 activePosition = nullptr;
88 idx = Threads.size(); // Starts from 0
92 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
93 // current active split point, or in some ancestor of the split point.
95 bool Thread::cutoff_occurred() const {
97 for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parentSplitPoint)
105 // Thread::available_to() checks whether the thread is available to help the
106 // thread 'master' at a split point. An obvious requirement is that thread must
107 // be idle. With more than two threads, this is not sufficient: If the thread is
108 // the master of some split point, it is only available as a slave to the slaves
109 // which are busy searching the split point at the top of slave's split point
110 // stack (the "helpful master concept" in YBWC terminology).
112 bool Thread::available_to(const Thread* master) const {
117 // Make a local copy to be sure it doesn't become zero under our feet while
118 // testing next condition and so leading to an out of bounds access.
119 const size_t size = splitPointsSize;
121 // No split points means that the thread is available as a slave for any
122 // other thread otherwise apply the "helpful master" concept if possible.
123 return !size || splitPoints[size - 1].slavesMask.test(master->idx);
127 // Thread::split() does the actual work of distributing the work at a node between
128 // several available threads. If it does not succeed in splitting the node
129 // (because no idle threads are available), the function immediately returns.
130 // If splitting is possible, a SplitPoint object is initialized with all the
131 // data that must be copied to the helper threads and then helper threads are
132 // informed that they have been assigned work. This will cause them to instantly
133 // leave their idle loops and call search(). When all threads have returned from
134 // search() then split() returns.
136 void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bestValue,
137 Move* bestMove, Depth depth, int moveCount,
138 MovePicker* movePicker, int nodeType, bool cutNode) {
141 assert(-VALUE_INFINITE < *bestValue && *bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
142 assert(depth >= Threads.minimumSplitDepth);
143 assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
145 // Pick and init the next available split point
146 SplitPoint& sp = splitPoints[splitPointsSize];
148 sp.masterThread = this;
149 sp.parentSplitPoint = activeSplitPoint;
150 sp.slavesMask = 0, sp.slavesMask.set(idx);
152 sp.bestValue = *bestValue;
153 sp.bestMove = *bestMove;
156 sp.nodeType = nodeType;
157 sp.cutNode = cutNode;
158 sp.movePicker = movePicker;
159 sp.moveCount = moveCount;
165 // Try to allocate available threads and ask them to start searching setting
166 // 'searching' flag. This must be done under lock protection to avoid concurrent
167 // allocation of the same slave by another master.
168 Threads.mutex.lock();
171 sp.allSlavesSearching = true; // Must be set under lock protection
173 activeSplitPoint = &sp;
174 activePosition = nullptr;
178 while ( sp.slavesMask.count() < MAX_SLAVES_PER_SPLITPOINT
179 && (slave = Threads.available_slave(this)) != nullptr)
181 sp.slavesMask.set(slave->idx);
182 slave->activeSplitPoint = &sp;
183 slave->searching = true; // Slave leaves idle_loop()
184 slave->notify_one(); // Could be sleeping
187 // Everything is set up. The master thread enters the idle loop, from which
188 // it will instantly launch a search, because its 'searching' flag is set.
189 // The thread will return from the idle loop when all slaves have finished
190 // their work at this split point.
192 Threads.mutex.unlock();
194 Thread::idle_loop(); // Force a call to base class idle_loop()
196 // In the helpful master concept, a master can help only a sub-tree of its
197 // split point and because everything is finished here, it's not possible
198 // for the master to be booked.
200 assert(!activePosition);
202 // We have returned from the idle loop, which means that all threads are
203 // finished. Note that setting 'searching' and decreasing splitPointsSize must
204 // be done under lock protection to avoid a race with Thread::available_to().
205 Threads.mutex.lock();
210 activeSplitPoint = sp.parentSplitPoint;
211 activePosition = &pos;
212 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
213 *bestMove = sp.bestMove;
214 *bestValue = sp.bestValue;
217 Threads.mutex.unlock();
221 // TimerThread::idle_loop() is where the timer thread waits Resolution milliseconds
222 // and then calls check_time(). When not searching, thread sleeps until it's woken up.
224 void TimerThread::idle_loop() {
228 std::unique_lock<std::mutex> lk(mutex);
231 sleepCondition.wait_for(lk, std::chrono::milliseconds(run ? Resolution : INT_MAX));
241 // MainThread::idle_loop() is where the main thread is parked waiting to be started
242 // when there is a new search. The main thread will launch all the slave threads.
244 void MainThread::idle_loop() {
248 std::unique_lock<std::mutex> lk(mutex);
252 while (!thinking && !exit)
254 Threads.sleepCondition.notify_one(); // Wake up the UI thread if needed
255 sleepCondition.wait(lk);
274 // ThreadPool::init() is called at startup to create and launch requested threads,
275 // that will go immediately to sleep. We cannot use a c'tor because Threads is a
276 // static object and we need a fully initialized engine at this point due to
277 // allocation of Endgames in Thread c'tor.
279 void ThreadPool::init() {
281 timer = new_thread<TimerThread>();
282 push_back(new_thread<MainThread>());
287 // ThreadPool::exit() terminates the threads before the program exits. Cannot be
288 // done in d'tor because threads must be terminated before freeing us.
290 void ThreadPool::exit() {
292 delete_thread(timer); // As first because check_time() accesses threads data
294 for (Thread* th : *this)
299 // ThreadPool::read_uci_options() updates internal threads parameters from the
300 // corresponding UCI options and creates/destroys threads to match the requested
301 // number. Thread objects are dynamically allocated to avoid creating all possible
302 // threads in advance (which include pawns and material tables), even if only a
303 // few are to be used.
305 void ThreadPool::read_uci_options() {
307 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
308 size_t requested = Options["Threads"];
310 assert(requested > 0);
312 // If zero (default) then set best minimum split depth automatically
313 if (!minimumSplitDepth)
314 minimumSplitDepth = requested < 8 ? 4 * ONE_PLY : 7 * ONE_PLY;
316 while (size() < requested)
317 push_back(new_thread<Thread>());
319 while (size() > requested)
321 delete_thread(back());
327 // ThreadPool::available_slave() tries to find an idle thread which is available
328 // as a slave for the thread 'master'.
330 Thread* ThreadPool::available_slave(const Thread* master) const {
332 for (Thread* th : *this)
333 if (th->available_to(master))
340 // ThreadPool::wait_for_think_finished() waits for main thread to finish the search
342 void ThreadPool::wait_for_think_finished() {
344 std::unique_lock<std::mutex> lk(main()->mutex);
345 sleepCondition.wait(lk, [&]{ return !main()->thinking; });
349 // ThreadPool::start_thinking() wakes up the main thread sleeping in
350 // MainThread::idle_loop() and starts a new search, then returns immediately.
352 void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
353 StateStackPtr& states) {
354 wait_for_think_finished();
356 SearchTime = Time::now(); // As early as possible
358 Signals.stopOnPonderhit = Signals.firstRootMove = false;
359 Signals.stop = Signals.failedLowAtRoot = false;
364 if (states.get()) // If we don't set a new position, preserve current state
366 SetupStates = std::move(states); // Ownership transfer here
367 assert(!states.get());
370 for (const auto& m : MoveList<LEGAL>(pos))
371 if ( limits.searchmoves.empty()
372 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
373 RootMoves.push_back(RootMove(m));
375 main()->thinking = true;
376 main()->notify_one(); // Starts main thread