2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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/>.
26 #include "ucioption.h"
28 using namespace Search;
30 ThreadPool Threads; // Global object
32 namespace { extern "C" {
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 long start_routine(Thread* th) { th->idle_loop(); return 0; }
42 // Thread c'tor starts a newly-created thread of execution that will call
43 // the the virtual function idle_loop(), going immediately to sleep.
45 Thread::Thread() : splitPoints() {
47 searching = exit = false;
48 maxPly = splitPointsSize = 0;
49 activeSplitPoint = NULL;
52 if (!thread_create(handle, start_routine, this))
54 std::cerr << "Failed to create thread number " << idx << std::endl;
60 // Thread d'tor waits for thread termination before to return
64 exit = true; // Search must be already finished
66 thread_join(handle); // Wait for thread termination
70 // TimerThread::idle_loop() is where the timer thread waits msec milliseconds
71 // and then calls check_time(). If msec is 0 thread sleeps until is woken up.
72 extern void check_time();
74 void TimerThread::idle_loop() {
81 sleepCondition.wait_for(mutex, msec ? msec : INT_MAX);
91 // MainThread::idle_loop() is where the main thread is parked waiting to be started
92 // when there is a new search. Main thread will launch all the slave threads.
94 void MainThread::idle_loop() {
102 while (!thinking && !exit)
104 Threads.sleepCondition.notify_one(); // Wake up UI thread if needed
105 sleepCondition.wait(mutex);
124 // Thread::notify_one() wakes up the thread when there is some search to do
126 void Thread::notify_one() {
129 sleepCondition.notify_one();
134 // Thread::wait_for() set the thread to sleep until condition 'b' turns true
136 void Thread::wait_for(volatile const bool& b) {
139 while (!b) sleepCondition.wait(mutex);
144 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
145 // current active split point, or in some ancestor of the split point.
147 bool Thread::cutoff_occurred() const {
149 for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parent)
157 // Thread::is_available_to() checks whether the thread is available to help the
158 // thread 'master' at a split point. An obvious requirement is that thread must
159 // be idle. With more than two threads, this is not sufficient: If the thread is
160 // the master of some split point, it is only available as a slave to the slaves
161 // which are busy searching the split point at the top of slaves split point
162 // stack (the "helpful master concept" in YBWC terminology).
164 bool Thread::is_available_to(Thread* master) const {
169 // Make a local copy to be sure doesn't become zero under our feet while
170 // testing next condition and so leading to an out of bound access.
171 int size = splitPointsSize;
173 // No split points means that the thread is available as a slave for any
174 // other thread otherwise apply the "helpful master" concept if possible.
175 return !size || (splitPoints[size - 1].slavesMask & (1ULL << master->idx));
179 // init() is called at startup to create and launch requested threads, that will
180 // go immediately to sleep due to 'sleepWhileIdle' set to true. We cannot use
181 // a c'tor becuase Threads is a static object and we need a fully initialized
182 // engine at this point due to allocation of Endgames in Thread c'tor.
184 void ThreadPool::init() {
186 sleepWhileIdle = true;
187 timer = new TimerThread();
188 threads.push_back(new MainThread());
193 // exit() cleanly terminates the threads before the program exits
195 void ThreadPool::exit() {
197 delete timer; // As first because check_time() accesses threads data
199 for (size_t i = 0; i < threads.size(); i++)
204 // read_uci_options() updates internal threads parameters from the corresponding
205 // UCI options and creates/destroys threads to match the requested number. Thread
206 // objects are dynamically allocated to avoid creating in advance all possible
207 // threads, with included pawns and material tables, if only few are used.
209 void ThreadPool::read_uci_options() {
211 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
212 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
213 size_t requested = Options["Threads"];
215 assert(requested > 0);
217 while (threads.size() < requested)
218 threads.push_back(new Thread());
220 while (threads.size() > requested)
222 delete threads.back();
228 // slave_available() tries to find an idle thread which is available as a slave
229 // for the thread 'master'.
231 bool ThreadPool::slave_available(Thread* master) const {
233 for (size_t i = 0; i < threads.size(); i++)
234 if (threads[i]->is_available_to(master))
241 // split() does the actual work of distributing the work at a node between
242 // several available threads. If it does not succeed in splitting the node
243 // (because no idle threads are available), the function immediately returns.
244 // If splitting is possible, a SplitPoint object is initialized with all the
245 // data that must be copied to the helper threads and then helper threads are
246 // told that they have been assigned work. This will cause them to instantly
247 // leave their idle loops and call search(). When all threads have returned from
248 // search() then split() returns.
251 Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
252 Value bestValue, Move* bestMove, Depth depth, Move threatMove,
253 int moveCount, MovePicker& mp, int nodeType) {
255 assert(pos.pos_is_ok());
256 assert(bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
257 assert(bestValue > -VALUE_INFINITE);
258 assert(depth >= Threads.minimumSplitDepth);
260 Thread* master = pos.this_thread();
262 assert(master->searching);
263 assert(master->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
265 // Pick the next available split point from the split point stack
266 SplitPoint& sp = master->splitPoints[master->splitPointsSize];
269 sp.parent = master->activeSplitPoint;
270 sp.slavesMask = 1ULL << master->idx;
272 sp.bestMove = *bestMove;
273 sp.threatMove = threatMove;
276 sp.nodeType = nodeType;
277 sp.bestValue = bestValue;
279 sp.moveCount = moveCount;
285 // Try to allocate available threads and ask them to start searching setting
286 // 'searching' flag. This must be done under lock protection to avoid concurrent
287 // allocation of the same slave by another master.
291 master->splitPointsSize++;
292 master->activeSplitPoint = &sp;
294 size_t slavesCnt = 1; // Master is always included
296 for (size_t i = 0; i < threads.size() && !Fake; ++i)
297 if (threads[i]->is_available_to(master) && ++slavesCnt <= maxThreadsPerSplitPoint)
299 sp.slavesMask |= 1ULL << threads[i]->idx;
300 threads[i]->activeSplitPoint = &sp;
301 threads[i]->searching = true; // Slave leaves idle_loop()
302 threads[i]->notify_one(); // Could be sleeping
308 // Everything is set up. The master thread enters the idle loop, from which
309 // it will instantly launch a search, because its 'searching' flag is set.
310 // The thread will return from the idle loop when all slaves have finished
311 // their work at this split point.
312 if (slavesCnt > 1 || Fake)
314 master->Thread::idle_loop(); // Force a call to base class idle_loop()
316 // In helpful master concept a master can help only a sub-tree of its split
317 // point, and because here is all finished is not possible master is booked.
318 assert(!master->searching);
321 // We have returned from the idle loop, which means that all threads are
322 // finished. Note that setting 'searching' and decreasing splitPointsSize is
323 // done under lock protection to avoid a race with Thread::is_available_to().
327 master->searching = true;
328 master->splitPointsSize--;
329 master->activeSplitPoint = sp.parent;
330 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
331 *bestMove = sp.bestMove;
339 // Explicit template instantiations
340 template Value ThreadPool::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
341 template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
344 // wait_for_think_finished() waits for main thread to go to sleep then returns
346 void ThreadPool::wait_for_think_finished() {
348 MainThread* t = main_thread();
350 while (t->thinking) sleepCondition.wait(t->mutex);
355 // start_thinking() wakes up the main thread sleeping in MainThread::idle_loop()
356 // so to start a new search, then returns immediately.
358 void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
359 const std::vector<Move>& searchMoves, StateStackPtr& states) {
360 wait_for_think_finished();
362 SearchTime = Time::now(); // As early as possible
364 Signals.stopOnPonderhit = Signals.firstRootMove = false;
365 Signals.stop = Signals.failedLowAtRoot = false;
369 SetupStates = states; // Ownership transfer here
372 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
373 if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
374 RootMoves.push_back(RootMove(ml.move()));
376 main_thread()->thinking = true;
377 main_thread()->notify_one(); // Starts main thread