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/>.
20 #include <algorithm> // For std::count
27 #include "ucioption.h"
29 using namespace Search;
31 ThreadPool Threads; // Global object
33 namespace { extern "C" {
35 // start_routine() is the C function which is called when a new thread
36 // is launched. It is a wrapper to the virtual function idle_loop().
38 long start_routine(Thread* th) { th->idle_loop(); return 0; }
43 // Thread c'tor starts a newly-created thread of execution that will call
44 // the the virtual function idle_loop(), going immediately to sleep.
46 Thread::Thread() : splitPoints() {
48 searching = exit = false;
49 maxPly = splitPointsSize = 0;
50 activeSplitPoint = NULL;
53 if (!thread_create(handle, start_routine, this))
55 std::cerr << "Failed to create thread number " << idx << std::endl;
61 // Thread d'tor waits for thread termination before to return
65 exit = true; // Search must be already finished
67 thread_join(handle); // Wait for thread termination
71 // TimerThread::idle_loop() is where the timer thread waits msec milliseconds
72 // and then calls check_time(). If msec is 0 thread sleeps until is woken up.
73 extern void check_time();
75 void TimerThread::idle_loop() {
82 sleepCondition.wait_for(mutex, msec ? msec : INT_MAX);
92 // MainThread::idle_loop() is where the main thread is parked waiting to be started
93 // when there is a new search. Main thread will launch all the slave threads.
95 void MainThread::idle_loop() {
103 while (!thinking && !exit)
105 Threads.sleepCondition.notify_one(); // Wake up UI thread if needed
106 sleepCondition.wait(mutex);
125 // Thread::notify_one() wakes up the thread when there is some search to do
127 void Thread::notify_one() {
130 sleepCondition.notify_one();
135 // Thread::wait_for() set the thread to sleep until condition 'b' turns true
137 void Thread::wait_for(volatile const bool& b) {
140 while (!b) sleepCondition.wait(mutex);
145 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
146 // current active split point, or in some ancestor of the split point.
148 bool Thread::cutoff_occurred() const {
150 for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parent)
158 // Thread::is_available_to() checks whether the thread is available to help the
159 // thread 'master' at a split point. An obvious requirement is that thread must
160 // be idle. With more than two threads, this is not sufficient: If the thread is
161 // the master of some split point, it is only available as a slave to the slaves
162 // which are busy searching the split point at the top of slaves split point
163 // stack (the "helpful master concept" in YBWC terminology).
165 bool Thread::is_available_to(Thread* master) const {
170 // Make a local copy to be sure doesn't become zero under our feet while
171 // testing next condition and so leading to an out of bound access.
172 int size = splitPointsSize;
174 // No split points means that the thread is available as a slave for any
175 // other thread otherwise apply the "helpful master" concept if possible.
176 return !size || (splitPoints[size - 1].slavesMask & (1ULL << master->idx));
180 // init() is called at startup to create and launch requested threads, that will
181 // go immediately to sleep due to 'sleepWhileIdle' set to true. We cannot use
182 // a c'tor becuase Threads is a static object and we need a fully initialized
183 // engine at this point due to allocation of Endgames in Thread c'tor.
185 void ThreadPool::init() {
187 sleepWhileIdle = true;
188 timer = new TimerThread();
189 threads.push_back(new MainThread());
194 // exit() cleanly terminates the threads before the program exits
196 void ThreadPool::exit() {
198 delete timer; // As first because check_time() accesses threads data
200 for (size_t i = 0; i < threads.size(); i++)
205 // read_uci_options() updates internal threads parameters from the corresponding
206 // UCI options and creates/destroys threads to match the requested number. Thread
207 // objects are dynamically allocated to avoid creating in advance all possible
208 // threads, with included pawns and material tables, if only few are used.
210 void ThreadPool::read_uci_options() {
212 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
213 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
214 size_t requested = Options["Threads"];
216 assert(requested > 0);
218 while (threads.size() < requested)
219 threads.push_back(new Thread());
221 while (threads.size() > requested)
223 delete threads.back();
229 // slave_available() tries to find an idle thread which is available as a slave
230 // for the thread 'master'.
232 bool ThreadPool::slave_available(Thread* master) const {
234 for (size_t i = 0; i < threads.size(); i++)
235 if (threads[i]->is_available_to(master))
242 // split() does the actual work of distributing the work at a node between
243 // several available threads. If it does not succeed in splitting the node
244 // (because no idle threads are available), the function immediately returns.
245 // If splitting is possible, a SplitPoint object is initialized with all the
246 // data that must be copied to the helper threads and then helper threads are
247 // told that they have been assigned work. This will cause them to instantly
248 // leave their idle loops and call search(). When all threads have returned from
249 // search() then split() returns.
252 Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
253 Value bestValue, Move* bestMove, Depth depth, Move threatMove,
254 int moveCount, MovePicker& mp, int nodeType) {
256 assert(pos.pos_is_ok());
257 assert(bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
258 assert(bestValue > -VALUE_INFINITE);
259 assert(depth >= Threads.minimumSplitDepth);
261 Thread* master = pos.this_thread();
263 assert(master->searching);
264 assert(master->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
266 // Pick the next available split point from the split point stack
267 SplitPoint& sp = master->splitPoints[master->splitPointsSize];
270 sp.parent = master->activeSplitPoint;
271 sp.slavesMask = 1ULL << master->idx;
273 sp.bestMove = *bestMove;
274 sp.threatMove = threatMove;
277 sp.nodeType = nodeType;
278 sp.bestValue = bestValue;
280 sp.moveCount = moveCount;
286 // Try to allocate available threads and ask them to start searching setting
287 // 'searching' flag. This must be done under lock protection to avoid concurrent
288 // allocation of the same slave by another master.
292 master->splitPointsSize++;
293 master->activeSplitPoint = &sp;
295 size_t slavesCnt = 1; // Master is always included
297 for (size_t i = 0; i < threads.size() && !Fake; ++i)
298 if (threads[i]->is_available_to(master) && ++slavesCnt <= maxThreadsPerSplitPoint)
300 sp.slavesMask |= 1ULL << threads[i]->idx;
301 threads[i]->activeSplitPoint = &sp;
302 threads[i]->searching = true; // Slave leaves idle_loop()
303 threads[i]->notify_one(); // Could be sleeping
309 // Everything is set up. The master thread enters the idle loop, from which
310 // it will instantly launch a search, because its 'searching' flag is set.
311 // The thread will return from the idle loop when all slaves have finished
312 // their work at this split point.
313 if (slavesCnt > 1 || Fake)
315 master->Thread::idle_loop(); // Force a call to base class idle_loop()
317 // In helpful master concept a master can help only a sub-tree of its split
318 // point, and because here is all finished is not possible master is booked.
319 assert(!master->searching);
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::is_available_to().
328 master->searching = true;
329 master->splitPointsSize--;
330 master->activeSplitPoint = sp.parent;
331 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
332 *bestMove = sp.bestMove;
340 // Explicit template instantiations
341 template Value ThreadPool::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
342 template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
345 // wait_for_think_finished() waits for main thread to go to sleep then returns
347 void ThreadPool::wait_for_think_finished() {
349 MainThread* t = main_thread();
351 while (t->thinking) sleepCondition.wait(t->mutex);
356 // start_thinking() wakes up the main thread sleeping in MainThread::idle_loop()
357 // so to start a new search, then returns immediately.
359 void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
360 const std::vector<Move>& searchMoves, StateStackPtr& states) {
361 wait_for_think_finished();
363 SearchTime = Time::now(); // As early as possible
365 Signals.stopOnPonderhit = Signals.firstRootMove = false;
366 Signals.stop = Signals.failedLowAtRoot = false;
370 SetupStates = states; // Ownership transfer here
373 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
374 if ( searchMoves.empty()
375 || std::count(searchMoves.begin(), searchMoves.end(), ml.move()))
376 RootMoves.push_back(RootMove(ml.move()));
378 main_thread()->thinking = true;
379 main_thread()->notify_one(); // Starts main thread