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 // start_routine() is the C function which is called when a new thread
37 // is launched. It is a wrapper to the virtual function idle_loop().
39 extern "C" { long start_routine(ThreadBase* th) { th->idle_loop(); return 0; } }
42 // Helpers to launch a thread after creation and joining before delete. Must be
43 // outside Thread c'tor and d'tor because the object must be fully initialized
44 // when start_routine (and hence virtual idle_loop) is called and when joining.
46 template<typename T> T* new_thread() {
48 thread_create(th->handle, start_routine, th); // Will go to sleep
52 void delete_thread(ThreadBase* th) {
55 th->exit = true; // Search must be already finished
59 thread_join(th->handle); // Wait for thread termination
66 // ThreadBase::notify_one() wakes up the thread when there is some work to do
68 void ThreadBase::notify_one() {
71 sleepCondition.notify_one();
76 // ThreadBase::wait_for() set the thread to sleep until 'condition' turns true
78 void ThreadBase::wait_for(volatile const bool& condition) {
81 while (!condition) sleepCondition.wait(mutex);
86 // Thread c'tor makes some init but does not launch any execution thread that
87 // will be started only when c'tor returns.
89 Thread::Thread() /* : splitPoints() */ { // Initialization of non POD broken in MSVC
94 activeSplitPoint = NULL;
95 activePosition = NULL;
96 idx = Threads.size(); // Starts from 0
100 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
101 // current active split point, or in some ancestor of the split point.
103 bool Thread::cutoff_occurred() const {
105 for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parentSplitPoint)
113 // Thread::available_to() checks whether the thread is available to help the
114 // thread 'master' at a split point. An obvious requirement is that thread must
115 // be idle. With more than two threads, this is not sufficient: If the thread is
116 // the master of some split point, it is only available as a slave to the slaves
117 // which are busy searching the split point at the top of slave's split point
118 // stack (the "helpful master concept" in YBWC terminology).
120 bool Thread::available_to(const Thread* master) const {
125 // Make a local copy to be sure it doesn't become zero under our feet while
126 // testing next condition and so leading to an out of bounds access.
127 const size_t size = splitPointsSize;
129 // No split points means that the thread is available as a slave for any
130 // other thread otherwise apply the "helpful master" concept if possible.
131 return !size || splitPoints[size - 1].slavesMask.test(master->idx);
135 // Thread::split() does the actual work of distributing the work at a node between
136 // several available threads. If it does not succeed in splitting the node
137 // (because no idle threads are available), the function immediately returns.
138 // If splitting is possible, a SplitPoint object is initialized with all the
139 // data that must be copied to the helper threads and then helper threads are
140 // informed that they have been assigned work. This will cause them to instantly
141 // leave their idle loops and call search(). When all threads have returned from
142 // search() then split() returns.
144 void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bestValue,
145 Move* bestMove, Depth depth, int moveCount,
146 MovePicker* movePicker, int nodeType, bool cutNode) {
149 assert(-VALUE_INFINITE < *bestValue && *bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
150 assert(depth >= Threads.minimumSplitDepth);
151 assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
153 // Pick and init the next available split point
154 SplitPoint& sp = splitPoints[splitPointsSize];
157 sp.parentSplitPoint = activeSplitPoint;
158 sp.slavesMask = 0, sp.slavesMask.set(idx);
160 sp.bestValue = *bestValue;
161 sp.bestMove = *bestMove;
164 sp.nodeType = nodeType;
165 sp.cutNode = cutNode;
166 sp.movePicker = movePicker;
167 sp.moveCount = moveCount;
173 // Try to allocate available threads and ask them to start searching setting
174 // 'searching' flag. This must be done under lock protection to avoid concurrent
175 // allocation of the same slave by another master.
176 Threads.mutex.lock();
179 sp.allSlavesSearching = true; // Must be set under lock protection
181 activeSplitPoint = &sp;
182 activePosition = NULL;
186 while ( sp.slavesMask.count() < MAX_SLAVES_PER_SPLITPOINT
187 && (slave = Threads.available_slave(this)) != NULL)
189 sp.slavesMask.set(slave->idx);
190 slave->activeSplitPoint = &sp;
191 slave->searching = true; // Slave leaves idle_loop()
192 slave->notify_one(); // Could be sleeping
195 // Everything is set up. The master thread enters the idle loop, from which
196 // it will instantly launch a search, because its 'searching' flag is set.
197 // The thread will return from the idle loop when all slaves have finished
198 // their work at this split point.
200 Threads.mutex.unlock();
202 Thread::idle_loop(); // Force a call to base class idle_loop()
204 // In the helpful master concept, a master can help only a sub-tree of its
205 // split point and because everything is finished here, it's not possible
206 // for the master to be booked.
208 assert(!activePosition);
210 // We have returned from the idle loop, which means that all threads are
211 // finished. Note that setting 'searching' and decreasing splitPointsSize must
212 // be done under lock protection to avoid a race with Thread::available_to().
213 Threads.mutex.lock();
218 activeSplitPoint = sp.parentSplitPoint;
219 activePosition = &pos;
220 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
221 *bestMove = sp.bestMove;
222 *bestValue = sp.bestValue;
225 Threads.mutex.unlock();
229 // TimerThread::idle_loop() is where the timer thread waits Resolution milliseconds
230 // and then calls check_time(). When not searching, thread sleeps until it's woken up.
232 void TimerThread::idle_loop() {
239 sleepCondition.wait_for(mutex, run ? Resolution : INT_MAX);
249 // MainThread::idle_loop() is where the main thread is parked waiting to be started
250 // when there is a new search. The main thread will launch all the slave threads.
252 void MainThread::idle_loop() {
260 while (!thinking && !exit)
262 Threads.sleepCondition.notify_one(); // Wake up the UI thread if needed
263 sleepCondition.wait(mutex);
282 // ThreadPool::init() is called at startup to create and launch requested threads,
283 // that will go immediately to sleep. We cannot use a c'tor because Threads is a
284 // static object and we need a fully initialized engine at this point due to
285 // allocation of Endgames in Thread c'tor.
287 void ThreadPool::init() {
289 timer = new_thread<TimerThread>();
290 push_back(new_thread<MainThread>());
295 // ThreadPool::exit() terminates the threads before the program exits. Cannot be
296 // done in d'tor because threads must be terminated before freeing us.
298 void ThreadPool::exit() {
300 delete_thread(timer); // As first because check_time() accesses threads data
302 for (iterator it = begin(); it != end(); ++it)
307 // ThreadPool::read_uci_options() updates internal threads parameters from the
308 // corresponding UCI options and creates/destroys threads to match the requested
309 // number. Thread objects are dynamically allocated to avoid creating all possible
310 // threads in advance (which include pawns and material tables), even if only a
311 // few are to be used.
313 void ThreadPool::read_uci_options() {
315 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
316 size_t requested = Options["Threads"];
318 assert(requested > 0);
320 // If zero (default) then set best minimum split depth automatically
321 if (!minimumSplitDepth)
322 minimumSplitDepth = requested < 8 ? 4 * ONE_PLY : 7 * ONE_PLY;
324 while (size() < requested)
325 push_back(new_thread<Thread>());
327 while (size() > requested)
329 delete_thread(back());
335 // ThreadPool::available_slave() tries to find an idle thread which is available
336 // as a slave for the thread 'master'.
338 Thread* ThreadPool::available_slave(const Thread* master) const {
340 for (const_iterator it = begin(); it != end(); ++it)
341 if ((*it)->available_to(master))
348 // ThreadPool::wait_for_think_finished() waits for main thread to finish the search
350 void ThreadPool::wait_for_think_finished() {
352 MainThread* th = main();
354 while (th->thinking) sleepCondition.wait(th->mutex);
359 // ThreadPool::start_thinking() wakes up the main thread sleeping in
360 // MainThread::idle_loop() and starts a new search, then returns immediately.
362 void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
363 StateStackPtr& states) {
364 wait_for_think_finished();
366 SearchTime = Time::now(); // As early as possible
368 Signals.stopOnPonderhit = Signals.firstRootMove = false;
369 Signals.stop = Signals.failedLowAtRoot = false;
374 if (states.get()) // If we don't set a new position, preserve current state
376 SetupStates = states; // Ownership transfer here
377 assert(!states.get());
380 for (MoveList<LEGAL> it(pos); *it; ++it)
381 if ( limits.searchmoves.empty()
382 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), *it))
383 RootMoves.push_back(RootMove(*it));
385 main()->thinking = true;
386 main()->notify_one(); // Starts main thread