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() {
79 while (!msec && !do_exit)
80 sleepCondition.wait_for(mutex, msec ? msec : INT_MAX);
87 // MainThread::idle_loop() is where the main thread is parked waiting to be started
88 // when there is a new search. Main thread will launch all the slave threads.
90 void MainThread::idle_loop() {
96 is_finished = true; // Always return to sleep after a search
99 while (is_finished && !do_exit)
101 Threads.sleepCondition.notify_one(); // Wake up UI thread if needed
102 sleepCondition.wait(mutex);
114 assert(is_searching);
119 // Thread::notify_one() wakes up the thread, normally at split time
121 void Thread::notify_one() {
124 sleepCondition.notify_one();
129 // Thread::wait_for() set the thread to sleep until condition 'b' turns true
131 void Thread::wait_for(volatile const bool& b) {
134 while (!b) sleepCondition.wait(mutex);
139 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
140 // current active split point, or in some ancestor of the split point.
142 bool Thread::cutoff_occurred() const {
144 for (SplitPoint* sp = curSplitPoint; sp; sp = sp->parent)
152 // Thread::is_available_to() checks whether the thread is available to help the
153 // thread 'master' at a split point. An obvious requirement is that thread must
154 // be idle. With more than two threads, this is not sufficient: If the thread is
155 // the master of some active split point, it is only available as a slave to the
156 // slaves which are busy searching the split point at the top of slaves split
157 // point stack (the "helpful master concept" in YBWC terminology).
159 bool Thread::is_available_to(Thread* master) const {
164 // Make a local copy to be sure doesn't become zero under our feet while
165 // testing next condition and so leading to an out of bound access.
166 int spCnt = splitPointsCnt;
168 // No active split points means that the thread is available as a slave for any
169 // other thread otherwise apply the "helpful master" concept if possible.
170 return !spCnt || (splitPoints[spCnt - 1].slavesMask & (1ULL << master->idx));
174 // init() is called at startup. Initializes lock and condition variable and
175 // launches requested threads sending them immediately to sleep. We cannot use
176 // a c'tor becuase Threads is a static object and we need a fully initialized
177 // engine at this point due to allocation of endgames in Thread c'tor.
179 void ThreadPool::init() {
181 sleepWhileIdle = true;
182 timer = new TimerThread();
183 threads.push_back(new MainThread());
188 // exit() cleanly terminates the threads before the program exits.
190 void ThreadPool::exit() {
192 delete timer; // As first becuase check_time() accesses threads data
194 for (size_t i = 0; i < threads.size(); i++)
199 // read_uci_options() updates internal threads parameters from the corresponding
200 // UCI options and creates/destroys threads to match the requested number. Thread
201 // objects are dynamically allocated to avoid creating in advance all possible
202 // threads, with included pawns and material tables, if only few are used.
204 void ThreadPool::read_uci_options() {
206 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
207 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
208 size_t requested = Options["Threads"];
210 assert(requested > 0);
212 while (threads.size() < requested)
213 threads.push_back(new Thread());
215 while (threads.size() > requested)
217 delete threads.back();
223 // available_slave_exists() tries to find an idle thread which is available as
224 // a slave for the thread 'master'.
226 bool ThreadPool::available_slave_exists(Thread* master) const {
228 for (size_t i = 0; i < threads.size(); i++)
229 if (threads[i]->is_available_to(master))
236 // split() does the actual work of distributing the work at a node between
237 // several available threads. If it does not succeed in splitting the node
238 // (because no idle threads are available, or because we have no unused split
239 // point objects), the function immediately returns. If splitting is possible, a
240 // SplitPoint object is initialized with all the data that must be copied to the
241 // helper threads and then helper threads are told that they have been assigned
242 // work. This will cause them to instantly leave their idle loops and call
243 // search(). When all threads have returned from search() then split() returns.
246 Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
247 Value bestValue, Move* bestMove, Depth depth, Move threatMove,
248 int moveCount, MovePicker& mp, int nodeType) {
250 assert(pos.pos_is_ok());
251 assert(bestValue > -VALUE_INFINITE);
252 assert(bestValue <= alpha);
253 assert(alpha < beta);
254 assert(beta <= VALUE_INFINITE);
255 assert(depth > DEPTH_ZERO);
257 Thread* master = pos.this_thread();
259 if (master->splitPointsCnt >= MAX_SPLITPOINTS_PER_THREAD)
262 // Pick the next available split point from the split point stack
263 SplitPoint& sp = master->splitPoints[master->splitPointsCnt];
265 sp.parent = master->curSplitPoint;
268 sp.slavesMask = 1ULL << master->idx;
270 sp.bestMove = *bestMove;
271 sp.threatMove = threatMove;
274 sp.nodeType = nodeType;
275 sp.bestValue = bestValue;
277 sp.moveCount = moveCount;
282 assert(master->is_searching);
284 master->curSplitPoint = &sp;
287 // Try to allocate available threads and ask them to start searching setting
288 // is_searching flag. This must be done under lock protection to avoid concurrent
289 // allocation of the same slave by another master.
293 for (size_t i = 0; i < threads.size() && !Fake; ++i)
294 if (threads[i]->is_available_to(master))
296 sp.slavesMask |= 1ULL << i;
297 threads[i]->curSplitPoint = &sp;
298 threads[i]->is_searching = true; // Slave leaves idle_loop()
299 threads[i]->notify_one(); // Could be sleeping
301 if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
305 master->splitPointsCnt++;
310 // Everything is set up. The master thread enters the idle loop, from which
311 // it will instantly launch a search, because its is_searching flag is set.
312 // The thread will return from the idle loop when all slaves have finished
313 // their work at this split point.
314 if (slavesCnt || Fake)
316 master->Thread::idle_loop(); // Force a call to base class idle_loop()
318 // In helpful master concept a master can help only a sub-tree of its split
319 // point, and because here is all finished is not possible master is booked.
320 assert(!master->is_searching);
323 // We have returned from the idle loop, which means that all threads are
324 // finished. Note that setting is_searching and decreasing splitPointsCnt is
325 // done under lock protection to avoid a race with Thread::is_available_to().
329 master->is_searching = true;
330 master->splitPointsCnt--;
331 master->curSplitPoint = sp.parent;
332 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
333 *bestMove = sp.bestMove;
341 // Explicit template instantiations
342 template Value ThreadPool::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
343 template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
346 // wait_for_search_finished() waits for main thread to go to sleep, this means
347 // search is finished. Then returns.
349 void ThreadPool::wait_for_search_finished() {
351 MainThread* t = main_thread();
353 while (!t->is_finished) sleepCondition.wait(t->mutex);
358 // start_searching() wakes up the main thread sleeping in main_loop() so to start
359 // a new search, then returns immediately.
361 void ThreadPool::start_searching(const Position& pos, const LimitsType& limits,
362 const std::vector<Move>& searchMoves, StateStackPtr& states) {
363 wait_for_search_finished();
365 SearchTime = Time::now(); // As early as possible
367 Signals.stopOnPonderhit = Signals.firstRootMove = false;
368 Signals.stop = Signals.failedLowAtRoot = false;
372 SetupStates = states; // Ownership transfer here
375 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
376 if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
377 RootMoves.push_back(RootMove(ml.move()));
379 main_thread()->is_finished = false;
380 main_thread()->notify_one(); // Starts main thread