2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 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 will 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) {
53 th->exit = true; // Search must be already finished
55 thread_join(th->handle); // Wait for thread termination
62 // notify_one() wakes up the thread when there is some work to do
64 void ThreadBase::notify_one() {
67 sleepCondition.notify_one();
72 // wait_for() set the thread to sleep until condition 'b' turns true
74 void ThreadBase::wait_for(volatile const bool& b) {
77 while (!b) sleepCondition.wait(mutex);
82 // Thread c'tor just inits data and does not launch any execution thread.
83 // Such a thread will only be started when c'tor returns.
85 Thread::Thread() /* : splitPoints() */ { // Value-initialization bug in MSVC
88 maxPly = splitPointsSize = 0;
89 activeSplitPoint = NULL;
90 activePosition = NULL;
91 idx = Threads.size(); // Starts from 0
95 // cutoff_occurred() checks whether a beta cutoff has occurred in the
96 // current active split point, or in some ancestor of the split point.
98 bool Thread::cutoff_occurred() const {
100 for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parentSplitPoint)
108 // Thread::available_to() checks whether the thread is available to help the
109 // thread 'master' at a split point. An obvious requirement is that thread must
110 // be idle. With more than two threads, this is not sufficient: If the thread is
111 // the master of some split point, it is only available as a slave to the slaves
112 // which are busy searching the split point at the top of slave's split point
113 // stack (the "helpful master concept" in YBWC terminology).
115 bool Thread::available_to(const Thread* master) const {
120 // Make a local copy to be sure it doesn't become zero under our feet while
121 // testing next condition and so leading to an out of bounds access.
122 const int size = splitPointsSize;
124 // No split points means that the thread is available as a slave for any
125 // other thread otherwise apply the "helpful master" concept if possible.
126 return !size || splitPoints[size - 1].slavesMask.test(master->idx);
130 // TimerThread::idle_loop() is where the timer thread waits msec milliseconds
131 // and then calls check_time(). If msec is 0 thread sleeps until it's woken up.
133 void TimerThread::idle_loop() {
140 sleepCondition.wait_for(mutex, run ? Resolution : INT_MAX);
150 // MainThread::idle_loop() is where the main thread is parked waiting to be started
151 // when there is a new search. The main thread will launch all the slave threads.
153 void MainThread::idle_loop() {
161 while (!thinking && !exit)
163 Threads.sleepCondition.notify_one(); // Wake up the UI thread if needed
164 sleepCondition.wait(mutex);
183 // init() is called at startup to create and launch requested threads, that will
184 // go immediately to sleep. We cannot use a c'tor because Threads is a static
185 // object and we need a fully initialized engine at this point due to allocation
186 // of Endgames in Thread c'tor.
188 void ThreadPool::init() {
190 timer = new_thread<TimerThread>();
191 push_back(new_thread<MainThread>());
196 // exit() cleanly terminates the threads before the program exits. Cannot be done in
197 // d'tor because we have to terminate the threads before to free ThreadPool object.
199 void ThreadPool::exit() {
201 delete_thread(timer); // As first because check_time() accesses threads data
203 for (iterator it = begin(); it != end(); ++it)
208 // read_uci_options() updates internal threads parameters from the corresponding
209 // UCI options and creates/destroys threads to match the requested number. Thread
210 // objects are dynamically allocated to avoid creating all possible threads
211 // in advance (which include pawns and material tables), even if only a few
214 void ThreadPool::read_uci_options() {
216 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
217 size_t requested = Options["Threads"];
219 assert(requested > 0);
221 // If zero (default) then set best minimum split depth automatically
222 if (!minimumSplitDepth)
223 minimumSplitDepth = requested < 8 ? 4 * ONE_PLY : 7 * ONE_PLY;
225 while (size() < requested)
226 push_back(new_thread<Thread>());
228 while (size() > requested)
230 delete_thread(back());
236 // available_slave() tries to find an idle thread which is available as a slave
237 // for the thread 'master'.
239 Thread* ThreadPool::available_slave(const Thread* master) const {
241 for (const_iterator it = begin(); it != end(); ++it)
242 if ((*it)->available_to(master))
249 // split() does the actual work of distributing the work at a node between
250 // several available threads. If it does not succeed in splitting the node
251 // (because no idle threads are available), the function immediately returns.
252 // If splitting is possible, a SplitPoint object is initialized with all the
253 // data that must be copied to the helper threads and then helper threads are
254 // told that they have been assigned work. This will cause them to instantly
255 // leave their idle loops and call search(). When all threads have returned from
256 // search() then split() returns.
258 void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bestValue,
259 Move* bestMove, Depth depth, int moveCount,
260 MovePicker* movePicker, int nodeType, bool cutNode) {
262 assert(pos.pos_is_ok());
263 assert(-VALUE_INFINITE < *bestValue && *bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
264 assert(depth >= Threads.minimumSplitDepth);
266 assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
268 // Pick the next available split point from the split point stack
269 SplitPoint& sp = splitPoints[splitPointsSize];
271 sp.masterThread = this;
272 sp.parentSplitPoint = activeSplitPoint;
273 sp.slavesMask = 0, sp.slavesMask.set(idx);
275 sp.bestValue = *bestValue;
276 sp.bestMove = *bestMove;
279 sp.nodeType = nodeType;
280 sp.cutNode = cutNode;
281 sp.movePicker = movePicker;
282 sp.moveCount = moveCount;
288 // Try to allocate available threads and ask them to start searching setting
289 // 'searching' flag. This must be done under lock protection to avoid concurrent
290 // allocation of the same slave by another master.
291 Threads.mutex.lock();
294 sp.allSlavesSearching = true; // Must be set under lock protection
296 activeSplitPoint = &sp;
297 activePosition = NULL;
299 for (Thread* slave; (slave = Threads.available_slave(this)) != NULL; )
301 sp.slavesMask.set(slave->idx);
302 slave->activeSplitPoint = &sp;
303 slave->searching = true; // Slave leaves idle_loop()
304 slave->notify_one(); // Could be sleeping
307 // Everything is set up. The master thread enters the idle loop, from which
308 // it will instantly launch a search, because its 'searching' flag is set.
309 // The thread will return from the idle loop when all slaves have finished
310 // their work at this split point.
312 Threads.mutex.unlock();
314 Thread::idle_loop(); // Force a call to base class idle_loop()
316 // In the helpful master concept, a master can help only a sub-tree of its
317 // split point and because everything is finished here, it's not possible
318 // for the master to be booked.
320 assert(!activePosition);
322 // We have returned from the idle loop, which means that all threads are
323 // finished. Note that setting 'searching' and decreasing splitPointsSize is
324 // done under lock protection to avoid a race with Thread::available_to().
325 Threads.mutex.lock();
330 activeSplitPoint = sp.parentSplitPoint;
331 activePosition = &pos;
332 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
333 *bestMove = sp.bestMove;
334 *bestValue = sp.bestValue;
337 Threads.mutex.unlock();
340 // wait_for_think_finished() waits for main thread to go to sleep then returns
342 void ThreadPool::wait_for_think_finished() {
344 MainThread* t = main();
346 while (t->thinking) sleepCondition.wait(t->mutex);
351 // start_thinking() wakes up the main thread sleeping in MainThread::idle_loop()
352 // so to start a new search, then returns immediately.
354 void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits, StateStackPtr& states) {
356 wait_for_think_finished();
358 SearchTime = Time::now(); // As early as possible
360 Signals.stopOnPonderhit = Signals.firstRootMove = false;
361 Signals.stop = Signals.failedLowAtRoot = false;
366 if (states.get()) // If we don't set a new position, preserve current state
368 SetupStates = states; // Ownership transfer here
369 assert(!states.get());
372 for (MoveList<LEGAL> it(pos); *it; ++it)
373 if ( limits.searchmoves.empty()
374 || std::count(limits.searchmoves.begin(), limits.searchmoves.end(), *it))
375 RootMoves.push_back(RootMove(*it));
377 main()->thinking = true;
378 main()->notify_one(); // Starts main thread