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 is_searching = do_exit = false;
48 maxPly = splitPointsCnt = 0;
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 do_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() {
100 is_finished = true; // Always return to sleep after a search
101 is_searching = false;
103 while (is_finished && !do_exit)
105 Threads.sleepCondition.notify_one(); // Wake up UI thread if needed
106 sleepCondition.wait(mutex);
118 assert(is_searching);
123 // Thread::notify_one() wakes up the thread, normally at split time
125 void Thread::notify_one() {
128 sleepCondition.notify_one();
133 // Thread::wait_for() set the thread to sleep until condition 'b' turns true
135 void Thread::wait_for(volatile const bool& b) {
138 while (!b) sleepCondition.wait(mutex);
143 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
144 // current active split point, or in some ancestor of the split point.
146 bool Thread::cutoff_occurred() const {
148 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
156 // Thread::is_available_to() checks whether the thread is available to help the
157 // thread 'master' at a split point. An obvious requirement is that thread must
158 // be idle. With more than two threads, this is not sufficient: If the thread is
159 // the master of some active split point, it is only available as a slave to the
160 // slaves which are busy searching the split point at the top of slaves split
161 // point stack (the "helpful master concept" in YBWC terminology).
163 bool Thread::is_available_to(Thread* master) const {
168 // Make a local copy to be sure doesn't become zero under our feet while
169 // testing next condition and so leading to an out of bound access.
170 int spCnt = splitPointsCnt;
172 // No active split points means that the thread is available as a slave for any
173 // other thread otherwise apply the "helpful master" concept if possible.
174 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master->idx));
178 // init() is called at startup. Initializes lock and condition variable and
179 // launches requested threads sending them immediately to sleep. We cannot use
180 // a c'tor becuase Threads is a static object and we need a fully initialized
181 // engine at this point due to allocation of endgames in Thread c'tor.
183 void ThreadPool::init() {
185 sleepWhileIdle = true;
186 timer = new TimerThread();
187 threads.push_back(new MainThread());
192 // exit() cleanly terminates the threads before the program exits.
194 void ThreadPool::exit() {
196 delete timer; // As first becuase check_time() accesses threads data
198 for (size_t i = 0; i < threads.size(); i++)
203 // read_uci_options() updates internal threads parameters from the corresponding
204 // UCI options and creates/destroys threads to match the requested number. Thread
205 // objects are dynamically allocated to avoid creating in advance all possible
206 // threads, with included pawns and material tables, if only few are used.
208 void ThreadPool::read_uci_options() {
210 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
211 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
212 size_t requested = Options["Threads"];
214 assert(requested > 0);
216 while (threads.size() < requested)
217 threads.push_back(new Thread());
219 while (threads.size() > requested)
221 delete threads.back();
227 // available_slave_exists() tries to find an idle thread which is available as
228 // a slave for the thread 'master'.
230 bool ThreadPool::available_slave_exists(Thread* master) const {
232 for (size_t i = 0; i < threads.size(); i++)
233 if (threads[i]->is_available_to(master))
240 // split() does the actual work of distributing the work at a node between
241 // several available threads. If it does not succeed in splitting the node
242 // (because no idle threads are available, or because we have no unused split
243 // point objects), the function immediately returns. If splitting is possible, a
244 // SplitPoint object is initialized with all the data that must be copied to the
245 // helper threads and then helper threads are told that they have been assigned
246 // work. This will cause them to instantly leave their idle loops and call
247 // search(). When all threads have returned from search() then split() returns.
250 Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
251 Value bestValue, Move* bestMove, Depth depth, Move threatMove,
252 int moveCount, MovePicker& mp, int nodeType) {
254 assert(pos.pos_is_ok());
255 assert(bestValue > -VALUE_INFINITE);
256 assert(bestValue <= alpha);
257 assert(alpha < beta);
258 assert(beta <= VALUE_INFINITE);
259 assert(depth > DEPTH_ZERO);
261 Thread* master = pos.this_thread();
263 if (master->splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
266 // Pick the next available split point from the split point stack
267 SplitPoint& sp = master->splitPoints[master->splitPointsCnt];
269 sp.parent = master->curSplitPoint;
272 sp.slavesMask = 1ULL << master->idx;
274 sp.bestMove = *bestMove;
275 sp.threatMove = threatMove;
278 sp.nodeType = nodeType;
279 sp.bestValue = bestValue;
281 sp.moveCount = moveCount;
286 assert(master->is_searching);
288 master->curSplitPoint = &sp;
291 // Try to allocate available threads and ask them to start searching setting
292 // is_searching flag. This must be done under lock protection to avoid concurrent
293 // allocation of the same slave by another master.
297 for (size_t i = 0; i < threads.size() && !Fake; ++i)
298 if (threads[i]->is_available_to(master))
300 sp.slavesMask |= 1ULL << i;
301 threads[i]->curSplitPoint = &sp;
302 threads[i]->is_searching = true; // Slave leaves idle_loop()
303 threads[i]->notify_one(); // Could be sleeping
305 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
309 master->splitPointsCnt++;
314 // Everything is set up. The master thread enters the idle loop, from which
315 // it will instantly launch a search, because its is_searching flag is set.
316 // The thread will return from the idle loop when all slaves have finished
317 // their work at this split point.
318 if (slavesCnt || Fake)
320 master->Thread::idle_loop(); // Force a call to base class idle_loop()
322 // In helpful master concept a master can help only a sub-tree of its split
323 // point, and because here is all finished is not possible master is booked.
324 assert(!master->is_searching);
327 // We have returned from the idle loop, which means that all threads are
328 // finished. Note that setting is_searching and decreasing splitPointsCnt is
329 // done under lock protection to avoid a race with Thread::is_available_to().
333 master->is_searching = true;
334 master->splitPointsCnt--;
335 master->curSplitPoint = sp.parent;
336 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
337 *bestMove = sp.bestMove;
345 // Explicit template instantiations
346 template Value ThreadPool::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
347 template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
350 // wait_for_search_finished() waits for main thread to go to sleep, this means
351 // search is finished. Then returns.
353 void ThreadPool::wait_for_search_finished() {
355 MainThread* t = main_thread();
357 while (!t->is_finished) sleepCondition.wait(t->mutex);
362 // start_searching() wakes up the main thread sleeping in main_loop() so to start
363 // a new search, then returns immediately.
365 void ThreadPool::start_searching(const Position& pos, const LimitsType& limits,
366 const std::vector<Move>& searchMoves, StateStackPtr& states) {
367 wait_for_search_finished();
369 SearchTime = Time::now(); // As early as possible
371 Signals.stopOnPonderhit = Signals.firstRootMove = false;
372 Signals.stop = Signals.failedLowAtRoot = false;
376 SetupStates = states; // Ownership transfer here
379 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
380 if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
381 RootMoves.push_back(RootMove(ml.move()));
383 main_thread()->is_finished = false;
384 main_thread()->notify_one(); // Starts main thread