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() {
41 std::thread* th = new T;
42 *th = std::thread(&T::idle_loop, (T*)th); // Will go to sleep
46 void delete_thread(ThreadBase* th) {
49 th->exit = true; // Search must be already finished
53 th->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<Mutex> lk(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<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::can_join() checks whether the thread is available to join the split
106 // point 'sp'. An obvious requirement is that thread must be idle. With more than
107 // two threads, this is not sufficient: If the thread is the master of some split
108 // point, it is only available as a slave for the split points below his active
109 // one (the "helpful master" concept in YBWC terminology).
111 bool Thread::can_join(const SplitPoint* sp) const {
116 // Make a local copy to be sure it doesn't become zero under our feet while
117 // testing next condition and so leading to an out of bounds access.
118 const size_t size = splitPointsSize;
120 // No split points means that the thread is available as a slave for any
121 // other thread otherwise apply the "helpful master" concept if possible.
122 return !size || splitPoints[size - 1].slavesMask.test(sp->master->idx);
126 // Thread::split() does the actual work of distributing the work at a node between
127 // several available threads. If it does not succeed in splitting the node
128 // (because no idle threads are available), the function immediately returns.
129 // If splitting is possible, a SplitPoint object is initialized with all the
130 // data that must be copied to the helper threads and then helper threads are
131 // informed that they have been assigned work. This will cause them to instantly
132 // leave their idle loops and call search(). When all threads have returned from
133 // search() then split() returns.
135 void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bestValue,
136 Move* bestMove, Depth depth, int moveCount,
137 MovePicker* movePicker, int nodeType, bool cutNode) {
140 assert(-VALUE_INFINITE < *bestValue && *bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
141 assert(depth >= Threads.minimumSplitDepth);
142 assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
144 // Pick and init the next available split point
145 SplitPoint& sp = splitPoints[splitPointsSize];
147 sp.spinlock.acquire(); // No contention here until we don't increment splitPointsSize
151 sp.parentSplitPoint = activeSplitPoint;
152 sp.slavesMask = 0, sp.slavesMask.set(idx);
154 sp.bestValue = *bestValue;
155 sp.bestMove = *bestMove;
158 sp.nodeType = nodeType;
159 sp.cutNode = cutNode;
160 sp.movePicker = movePicker;
161 sp.moveCount = moveCount;
166 sp.allSlavesSearching = true; // Must be set under lock protection
169 activeSplitPoint = &sp;
170 activePosition = nullptr;
173 // Try to allocate available threads
176 while ( sp.slavesMask.count() < MAX_SLAVES_PER_SPLITPOINT
177 && (slave = Threads.available_slave(&sp)) != nullptr)
179 slave->spinlock.acquire();
181 if (slave->can_join(activeSplitPoint))
183 activeSplitPoint->slavesMask.set(slave->idx);
184 slave->activeSplitPoint = activeSplitPoint;
185 slave->searching = true;
188 slave->spinlock.release();
191 // Everything is set up. The master thread enters the idle loop, from which
192 // it will instantly launch a search, because its 'searching' flag is set.
193 // The thread will return from the idle loop when all slaves have finished
194 // their work at this split point.
195 sp.spinlock.release();
197 Thread::idle_loop(); // Force a call to base class idle_loop()
199 sp.spinlock.acquire();
202 // In the helpful master concept, a master can help only a sub-tree of its
203 // split point and because everything is finished here, it's not possible
204 // for the master to be booked.
206 assert(!activePosition);
210 // We have returned from the idle loop, which means that all threads are
211 // finished. Note that decreasing splitPointsSize must be done under lock
212 // protection to avoid a race with Thread::can_join().
214 activeSplitPoint = sp.parentSplitPoint;
215 activePosition = &pos;
216 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
217 *bestMove = sp.bestMove;
218 *bestValue = sp.bestValue;
221 sp.spinlock.release();
225 // TimerThread::idle_loop() is where the timer thread waits Resolution milliseconds
226 // and then calls check_time(). When not searching, thread sleeps until it's woken up.
228 void TimerThread::idle_loop() {
232 std::unique_lock<Mutex> lk(mutex);
235 sleepCondition.wait_for(lk, std::chrono::milliseconds(run ? Resolution : INT_MAX));
245 // MainThread::idle_loop() is where the main thread is parked waiting to be started
246 // when there is a new search. The main thread will launch all the slave threads.
248 void MainThread::idle_loop() {
252 std::unique_lock<Mutex> lk(mutex);
256 while (!thinking && !exit)
258 sleepCondition.notify_one(); // Wake up the UI thread if needed
259 sleepCondition.wait(lk);
278 // MainThread::join() waits for main thread to finish the search
280 void MainThread::join() {
282 std::unique_lock<Mutex> lk(mutex);
283 sleepCondition.wait(lk, [&]{ return !thinking; });
287 // ThreadPool::init() is called at startup to create and launch requested threads,
288 // that will go immediately to sleep. We cannot use a c'tor because Threads is a
289 // static object and we need a fully initialized engine at this point due to
290 // allocation of Endgames in Thread c'tor.
292 void ThreadPool::init() {
294 timer = new_thread<TimerThread>();
295 push_back(new_thread<MainThread>());
300 // ThreadPool::exit() terminates the threads before the program exits. Cannot be
301 // done in d'tor because threads must be terminated before freeing us.
303 void ThreadPool::exit() {
305 delete_thread(timer); // As first because check_time() accesses threads data
308 for (Thread* th : *this)
311 clear(); // Get rid of stale pointers
315 // ThreadPool::read_uci_options() updates internal threads parameters from the
316 // corresponding UCI options and creates/destroys threads to match the requested
317 // number. Thread objects are dynamically allocated to avoid creating all possible
318 // threads in advance (which include pawns and material tables), even if only a
319 // few are to be used.
321 void ThreadPool::read_uci_options() {
323 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
324 size_t requested = Options["Threads"];
326 assert(requested > 0);
328 while (size() < requested)
329 push_back(new_thread<Thread>());
331 while (size() > requested)
333 delete_thread(back());
339 // ThreadPool::available_slave() tries to find an idle thread which is available
340 // to join SplitPoint 'sp'.
342 Thread* ThreadPool::available_slave(const SplitPoint* sp) const {
344 for (Thread* th : *this)
345 if (th->can_join(sp))
352 // ThreadPool::start_thinking() wakes up the main thread sleeping in
353 // MainThread::idle_loop() and starts a new search, then returns immediately.
355 void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
356 StateStackPtr& states) {
359 Signals.stopOnPonderhit = Signals.firstRootMove = false;
360 Signals.stop = Signals.failedLowAtRoot = false;
365 if (states.get()) // If we don't set a new position, preserve current state
367 SetupStates = std::move(states); // Ownership transfer here
368 assert(!states.get());
371 for (const auto& m : MoveList<LEGAL>(pos))
372 if ( limits.searchmoves.empty()
373 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), m))
374 RootMoves.push_back(RootMove(m));
376 main()->thinking = true;
377 main()->notify_one(); // Wake up main thread: 'thinking' must be already set