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
26 #include "ucioption.h"
28 using namespace Search;
30 ThreadPool Threads; // Global object
34 // start_routine() is the C function which is called when a new thread
35 // is launched. It is a wrapper to the virtual function idle_loop().
37 extern "C" { long start_routine(ThreadBase* th) { th->idle_loop(); return 0; } }
40 // Helpers to launch a thread after creation and joining before delete. Must be
41 // outside Thread c'tor and d'tor because the object will be fully initialized
42 // when start_routine (and hence virtual idle_loop) is called and when joining.
44 template<typename T> T* new_thread() {
46 thread_create(th->handle, start_routine, th); // Will go to sleep
50 void delete_thread(ThreadBase* th) {
51 th->exit = true; // Search must be already finished
53 thread_join(th->handle); // Wait for thread termination
60 // ThreadBase::notify_one() wakes up the thread when there is some work to do
62 void ThreadBase::notify_one() {
65 sleepCondition.notify_one();
70 // ThreadBase::wait_for() set the thread to sleep until condition 'b' turns true
72 void ThreadBase::wait_for(volatile const bool& b) {
75 while (!b) sleepCondition.wait(mutex);
80 // Thread c'tor just inits data and does not launch any execution thread.
81 // Such a thread will only be started when c'tor returns.
83 Thread::Thread() /* : splitPoints() */ { // Value-initialization bug in MSVC
86 maxPly = splitPointsSize = 0;
87 activeSplitPoint = NULL;
88 activePosition = NULL;
93 // TimerThread::idle_loop() is where the timer thread waits msec milliseconds
94 // and then calls check_time(). If msec is 0 thread sleeps until it's woken up.
95 extern void check_time();
97 void TimerThread::idle_loop() {
104 sleepCondition.wait_for(mutex, run ? Resolution : INT_MAX);
114 // MainThread::idle_loop() is where the main thread is parked waiting to be started
115 // when there is a new search. The main thread will launch all the slave threads.
117 void MainThread::idle_loop() {
125 while (!thinking && !exit)
127 Threads.sleepCondition.notify_one(); // Wake up the UI thread if needed
128 sleepCondition.wait(mutex);
147 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
148 // current active split point, or in some ancestor of the split point.
150 bool Thread::cutoff_occurred() const {
152 for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parentSplitPoint)
160 // Thread::available_to() checks whether the thread is available to help the
161 // thread 'master' at a split point. An obvious requirement is that thread must
162 // be idle. With more than two threads, this is not sufficient: If the thread is
163 // the master of some split point, it is only available as a slave to the slaves
164 // which are busy searching the split point at the top of slave's split point
165 // stack (the "helpful master concept" in YBWC terminology).
167 bool Thread::available_to(const Thread* master) const {
172 // Make a local copy to be sure it doesn't become zero under our feet while
173 // testing next condition and so leading to an out of bounds access.
174 int size = splitPointsSize;
176 // No split points means that the thread is available as a slave for any
177 // other thread otherwise apply the "helpful master" concept if possible.
178 return !size || (splitPoints[size - 1].slavesMask & (1ULL << master->idx));
182 // init() is called at startup to create and launch requested threads, that will
183 // go immediately to sleep due to 'sleepWhileIdle' set to true. We cannot use
184 // a c'tor because Threads is a static object and we need a fully initialized
185 // engine at this point due to allocation of Endgames in Thread c'tor.
187 void ThreadPool::init() {
189 sleepWhileIdle = true;
190 timer = new_thread<TimerThread>();
191 push_back(new_thread<MainThread>());
196 // exit() cleanly terminates the threads before the program exits
198 void ThreadPool::exit() {
200 delete_thread(timer); // As first because check_time() accesses threads data
202 for (iterator it = begin(); it != end(); ++it)
207 // read_uci_options() updates internal threads parameters from the corresponding
208 // UCI options and creates/destroys threads to match the requested number. Thread
209 // objects are dynamically allocated to avoid creating all possible threads
210 // in advance (which include pawns and material tables), even if only a few
213 void ThreadPool::read_uci_options() {
215 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
216 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
217 size_t requested = Options["Threads"];
219 assert(requested > 0);
221 // Value 0 has a special meaning: We determine the optimal minimum split depth
222 // automatically. Anyhow the minimumSplitDepth should never be under 4 plies.
223 if (!minimumSplitDepth)
224 minimumSplitDepth = (requested < 8 ? 4 : 7) * ONE_PLY;
226 minimumSplitDepth = std::max(4 * ONE_PLY, minimumSplitDepth);
228 while (size() < requested)
229 push_back(new_thread<Thread>());
231 while (size() > requested)
233 delete_thread(back());
239 // slave_available() tries to find an idle thread which is available as a slave
240 // for the thread 'master'.
242 Thread* ThreadPool::available_slave(const Thread* master) const {
244 for (const_iterator it = begin(); it != end(); ++it)
245 if ((*it)->available_to(master))
252 // split() does the actual work of distributing the work at a node between
253 // several available threads. If it does not succeed in splitting the node
254 // (because no idle threads are available), the function immediately returns.
255 // If splitting is possible, a SplitPoint object is initialized with all the
256 // data that must be copied to the helper threads and then helper threads are
257 // told that they have been assigned work. This will cause them to instantly
258 // leave their idle loops and call search(). When all threads have returned from
259 // search() then split() returns.
262 void Thread::split(Position& pos, const Stack* ss, Value alpha, Value beta, Value* bestValue,
263 Move* bestMove, Depth depth, int moveCount,
264 MovePicker* movePicker, int nodeType, bool cutNode) {
266 assert(pos.pos_is_ok());
267 assert(*bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
268 assert(*bestValue > -VALUE_INFINITE);
269 assert(depth >= Threads.minimumSplitDepth);
271 assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
273 // Pick the next available split point from the split point stack
274 SplitPoint& sp = splitPoints[splitPointsSize];
276 sp.masterThread = this;
277 sp.parentSplitPoint = activeSplitPoint;
278 sp.slavesMask = 1ULL << idx;
280 sp.bestValue = *bestValue;
281 sp.bestMove = *bestMove;
284 sp.nodeType = nodeType;
285 sp.cutNode = cutNode;
286 sp.movePicker = movePicker;
287 sp.moveCount = moveCount;
293 // Try to allocate available threads and ask them to start searching setting
294 // 'searching' flag. This must be done under lock protection to avoid concurrent
295 // allocation of the same slave by another master.
296 Threads.mutex.lock();
300 activeSplitPoint = &sp;
301 activePosition = NULL;
303 size_t slavesCnt = 1; // This thread is always included
306 while ( (slave = Threads.available_slave(this)) != NULL
307 && ++slavesCnt <= Threads.maxThreadsPerSplitPoint && !Fake)
309 sp.slavesMask |= 1ULL << slave->idx;
310 slave->activeSplitPoint = &sp;
311 slave->searching = true; // Slave leaves idle_loop()
312 slave->notify_one(); // Could be sleeping
315 // Everything is set up. The master thread enters the idle loop, from which
316 // it will instantly launch a search, because its 'searching' flag is set.
317 // The thread will return from the idle loop when all slaves have finished
318 // their work at this split point.
319 if (slavesCnt > 1 || Fake)
322 Threads.mutex.unlock();
324 Thread::idle_loop(); // Force a call to base class idle_loop()
326 // In the helpful master concept, a master can help only a sub-tree of its
327 // split point and because everything is finished here, it's not possible
328 // for the master to be booked.
330 assert(!activePosition);
332 // We have returned from the idle loop, which means that all threads are
333 // finished. Note that setting 'searching' and decreasing splitPointsSize is
334 // done under lock protection to avoid a race with Thread::available_to().
335 Threads.mutex.lock();
341 activeSplitPoint = sp.parentSplitPoint;
342 activePosition = &pos;
343 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
344 *bestMove = sp.bestMove;
345 *bestValue = sp.bestValue;
348 Threads.mutex.unlock();
351 // Explicit template instantiations
352 template void Thread::split<false>(Position&, const Stack*, Value, Value, Value*, Move*, Depth, int, MovePicker*, int, bool);
353 template void Thread::split< true>(Position&, const Stack*, Value, Value, Value*, Move*, Depth, int, MovePicker*, int, bool);
356 // wait_for_think_finished() waits for main thread to go to sleep then returns
358 void ThreadPool::wait_for_think_finished() {
360 MainThread* t = main();
362 while (t->thinking) sleepCondition.wait(t->mutex);
367 // start_thinking() wakes up the main thread sleeping in MainThread::idle_loop()
368 // so to start a new search, then returns immediately.
370 void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
371 const std::vector<Move>& searchMoves, StateStackPtr& states) {
372 wait_for_think_finished();
374 SearchTime = Time::now(); // As early as possible
376 Signals.stopOnPonderhit = Signals.firstRootMove = false;
377 Signals.stop = Signals.failedLowAtRoot = false;
382 if (states.get()) // If we don't set a new position, preserve current state
384 SetupStates = states; // Ownership transfer here
385 assert(!states.get());
388 for (MoveList<LEGAL> it(pos); *it; ++it)
389 if ( searchMoves.empty()
390 || std::count(searchMoves.begin(), searchMoves.end(), *it))
391 RootMoves.push_back(RootMove(*it));
393 main()->thinking = true;
394 main()->notify_one(); // Starts main thread