2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
23 #include "ucioption.h"
25 ThreadsManager Threads; // Global object definition
27 namespace { extern "C" {
29 // start_routine() is the C function which is called when a new thread
30 // is launched. It simply calls idle_loop() of the supplied thread.
31 // There are two versions of this function; one for POSIX threads and
32 // one for Windows threads.
36 DWORD WINAPI start_routine(LPVOID thread) {
38 ((Thread*)thread)->idle_loop(NULL);
44 void* start_routine(void* thread) {
46 ((Thread*)thread)->idle_loop(NULL);
55 // wake_up() wakes up the thread, normally at the beginning of the search or,
56 // if "sleeping threads" is used, when there is some work to do.
58 void Thread::wake_up() {
60 lock_grab(&sleepLock);
61 cond_signal(&sleepCond);
62 lock_release(&sleepLock);
66 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
67 // active split point, or in some ancestor of the split point.
69 bool Thread::cutoff_occurred() const {
71 for (SplitPoint* sp = splitPoint; sp; sp = sp->parent)
72 if (sp->is_betaCutoff)
78 // is_available_to() checks whether the thread is available to help the thread with
79 // threadID "master" at a split point. An obvious requirement is that thread must be
80 // idle. With more than two threads, this is not by itself sufficient: If the thread
81 // is the master of some active split point, it is only available as a slave to the
82 // threads which are busy searching the split point at the top of "slave"'s split
83 // point stack (the "helpful master concept" in YBWC terminology).
85 bool Thread::is_available_to(int master) const {
87 if (state != AVAILABLE)
90 // Make a local copy to be sure doesn't become zero under our feet while
91 // testing next condition and so leading to an out of bound access.
92 int localActiveSplitPoints = activeSplitPoints;
94 // No active split points means that the thread is available as a slave for any
95 // other thread otherwise apply the "helpful master" concept if possible.
96 if ( !localActiveSplitPoints
97 || splitPoints[localActiveSplitPoints - 1].is_slave[master])
104 // read_uci_options() updates number of active threads and other internal
105 // parameters according to the UCI options values. It is called before
106 // to start a new search.
108 void ThreadsManager::read_uci_options() {
110 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
111 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
112 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
114 set_size(Options["Threads"].value<int>());
118 // set_size() changes the number of active threads and raises do_sleep flag for
119 // all the unused threads that will go immediately to sleep.
121 void ThreadsManager::set_size(int cnt) {
123 assert(cnt > 0 && cnt <= MAX_THREADS);
127 for (int i = 0; i < MAX_THREADS; i++)
128 if (i < activeThreads)
130 // Dynamically allocate pawn and material hash tables according to the
131 // number of active threads. This avoids preallocating memory for all
132 // possible threads if only few are used as, for instance, on mobile
133 // devices where memory is scarce and allocating for MAX_THREADS could
134 // even result in a crash.
135 threads[i].pawnTable.init();
136 threads[i].materialTable.init();
138 threads[i].do_sleep = false;
141 threads[i].do_sleep = true;
145 // init() is called during startup. Initializes locks and condition variables
146 // and launches all threads sending them immediately to sleep.
148 void ThreadsManager::init() {
150 // Initialize threads lock, used when allocating slaves during splitting
151 lock_init(&threadsLock);
153 // Initialize sleep and split point locks
154 for (int i = 0; i < MAX_THREADS; i++)
156 lock_init(&threads[i].sleepLock);
157 cond_init(&threads[i].sleepCond);
159 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
160 lock_init(&(threads[i].splitPoints[j].lock));
163 // Initialize main thread's associated data
164 threads[0].state = Thread::SEARCHING;
165 threads[0].threadID = 0;
166 set_size(1); // This makes all the threads but the main to go to sleep
168 // Create and launch all the threads but the main that is already running,
169 // threads will go immediately to sleep.
170 for (int i = 1; i < MAX_THREADS; i++)
172 threads[i].state = Thread::AVAILABLE;
173 threads[i].threadID = i;
175 #if defined(_MSC_VER)
176 threads[i].handle = CreateThread(NULL, 0, start_routine, (LPVOID)&threads[i], 0, NULL);
177 bool ok = (threads[i].handle != NULL);
179 bool ok = (pthread_create(&threads[i].handle, NULL, start_routine, (void*)&threads[i]) == 0);
184 std::cerr << "Failed to create thread number " << i << std::endl;
185 ::exit(EXIT_FAILURE);
191 // exit() is called to cleanly terminate the threads when the program finishes
193 void ThreadsManager::exit() {
195 for (int i = 0; i < MAX_THREADS; i++)
197 // Wake up all the slave threads and wait for termination
200 threads[i].do_terminate = true;
201 threads[i].wake_up();
203 #if defined(_MSC_VER)
204 WaitForSingleObject(threads[i].handle, 0);
205 CloseHandle(threads[i].handle);
207 pthread_join(threads[i].handle, NULL);
211 // Now we can safely destroy locks and wait conditions
212 lock_destroy(&threads[i].sleepLock);
213 cond_destroy(&threads[i].sleepCond);
215 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
216 lock_destroy(&(threads[i].splitPoints[j].lock));
219 lock_destroy(&threadsLock);
223 // available_slave_exists() tries to find an idle thread which is available as
224 // a slave for the thread with threadID "master".
226 bool ThreadsManager::available_slave_exists(int master) const {
228 assert(master >= 0 && master < activeThreads);
230 for (int i = 0; i < activeThreads; i++)
231 if (i != master && threads[i].is_available_to(master))
238 // split() does the actual work of distributing the work at a node between
239 // several available threads. If it does not succeed in splitting the
240 // node (because no idle threads are available, or because we have no unused
241 // split point objects), the function immediately returns. If splitting is
242 // possible, a SplitPoint object is initialized with all the data that must be
243 // copied to the helper threads and we tell our helper threads that they have
244 // been assigned work. This will cause them to instantly leave their idle loops and
245 // call search().When all threads have returned from search() then split() returns.
248 Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value beta,
249 Value bestValue, Depth depth, Move threatMove,
250 int moveCount, MovePicker* mp, int nodeType) {
252 assert(bestValue >= -VALUE_INFINITE);
253 assert(bestValue <= alpha);
254 assert(alpha < beta);
255 assert(beta <= VALUE_INFINITE);
256 assert(depth > DEPTH_ZERO);
257 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
258 assert(activeThreads > 1);
260 int i, master = pos.thread();
261 Thread& masterThread = threads[master];
263 // If we already have too many active split points, don't split
264 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
267 // Pick the next available split point object from the split point stack
268 SplitPoint* sp = masterThread.splitPoints + masterThread.activeSplitPoints;
270 // Initialize the split point object
271 sp->parent = masterThread.splitPoint;
273 sp->is_betaCutoff = false;
275 sp->threatMove = threatMove;
278 sp->nodeType = nodeType;
279 sp->bestValue = bestValue;
281 sp->moveCount = moveCount;
285 for (i = 0; i < activeThreads; i++)
286 sp->is_slave[i] = false;
288 // If we are here it means we are not available
289 assert(masterThread.state == Thread::SEARCHING);
291 int workersCnt = 1; // At least the master is included
293 // Try to allocate available threads and ask them to start searching setting
294 // the state to Thread::WORKISWAITING, this must be done under lock protection
295 // to avoid concurrent allocation of the same slave by another master.
296 lock_grab(&threadsLock);
298 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
299 if (i != master && threads[i].is_available_to(master))
302 sp->is_slave[i] = true;
303 threads[i].splitPoint = sp;
305 // This makes the slave to exit from idle_loop()
306 threads[i].state = Thread::SEARCHING;
308 if (useSleepingThreads)
309 threads[i].wake_up();
312 lock_release(&threadsLock);
314 // We failed to allocate even one slave, return
315 if (!Fake && workersCnt == 1)
318 masterThread.splitPoint = sp;
319 masterThread.activeSplitPoints++;
321 // Everything is set up. The master thread enters the idle loop, from
322 // which it will instantly launch a search, because its state is
323 // Thread::WORKISWAITING. We send the split point as a second parameter to
324 // the idle loop, which means that the main thread will return from the idle
325 // loop when all threads have finished their work at this split point.
326 masterThread.idle_loop(sp);
328 // In helpful master concept a master can help only a sub-tree, and
329 // because here is all finished is not possible master is booked.
330 assert(masterThread.state == Thread::AVAILABLE);
332 // We have returned from the idle loop, which means that all threads are
333 // finished. Note that changing state and decreasing activeSplitPoints is done
334 // under lock protection to avoid a race with Thread::is_available_to().
335 lock_grab(&threadsLock);
337 masterThread.state = Thread::SEARCHING;
338 masterThread.activeSplitPoints--;
340 lock_release(&threadsLock);
342 masterThread.splitPoint = sp->parent;
343 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
345 return sp->bestValue;
348 // Explicit template instantiations
349 template Value ThreadsManager::split<false>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
350 template Value ThreadsManager::split<true>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);