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() with the supplied threadID.
31 // There are two versions of this function; one for POSIX threads and
32 // one for Windows threads.
36 DWORD WINAPI start_routine(LPVOID threadID) {
38 Threads.idle_loop(*(int*)threadID, NULL);
44 void* start_routine(void* threadID) {
46 Threads.idle_loop(*(int*)threadID, 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
67 // the thread's currently active split point, or in some ancestor of
68 // the current split point.
70 bool Thread::cutoff_occurred() const {
72 for (SplitPoint* sp = splitPoint; sp; sp = sp->parent)
73 if (sp->is_betaCutoff)
79 // is_available_to() checks whether the thread is available to help the thread with
80 // threadID "master" at a split point. An obvious requirement is that thread must be
81 // idle. With more than two threads, this is not by itself sufficient: If the thread
82 // is the master of some active split point, it is only available as a slave to the
83 // threads which are busy searching the split point at the top of "slave"'s split
84 // point stack (the "helpful master concept" in YBWC terminology).
86 bool Thread::is_available_to(int master) const {
88 if (state != AVAILABLE)
91 // Make a local copy to be sure doesn't become zero under our feet while
92 // testing next condition and so leading to an out of bound access.
93 int localActiveSplitPoints = activeSplitPoints;
95 // No active split points means that the thread is available as a slave for any
96 // other thread otherwise apply the "helpful master" concept if possible.
97 if ( !localActiveSplitPoints
98 || splitPoints[localActiveSplitPoints - 1].is_slave[master])
105 // read_uci_options() updates number of active threads and other internal
106 // parameters according to the UCI options values. It is called before
107 // to start a new search.
109 void ThreadsManager::read_uci_options() {
111 maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
112 minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
113 useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
114 activeThreads = Options["Threads"].value<int>();
118 // init() is called during startup. Initializes locks and condition variables
119 // and launches all threads sending them immediately to sleep.
121 void ThreadsManager::init() {
123 int threadID[MAX_THREADS];
125 // This flag is needed to properly end the threads when program exits
126 allThreadsShouldExit = false;
128 // Threads will sent to sleep as soon as created, only main thread is kept alive
130 threads[0].state = Thread::SEARCHING;
132 // Allocate pawn and material hash tables for main thread
135 lock_init(&threadsLock);
137 // Initialize thread and split point locks
138 for (int i = 0; i < MAX_THREADS; i++)
140 lock_init(&threads[i].sleepLock);
141 cond_init(&threads[i].sleepCond);
143 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
144 lock_init(&(threads[i].splitPoints[j].lock));
147 // Create and startup all the threads but the main that is already running
148 for (int i = 1; i < MAX_THREADS; i++)
150 threads[i].state = Thread::INITIALIZING;
153 #if defined(_MSC_VER)
154 bool ok = (CreateThread(NULL, 0, start_routine, (LPVOID)&threadID[i], 0, NULL) != NULL);
157 bool ok = (pthread_create(&pthreadID, NULL, start_routine, (void*)&threadID[i]) == 0);
158 pthread_detach(pthreadID);
162 std::cout << "Failed to create thread number " << i << std::endl;
163 ::exit(EXIT_FAILURE);
166 // Wait until the thread has finished launching and is gone to sleep
167 while (threads[i].state == Thread::INITIALIZING) {}
172 // exit() is called to cleanly exit the threads when the program finishes
174 void ThreadsManager::exit() {
176 // Force the woken up threads to exit idle_loop() and hence terminate
177 allThreadsShouldExit = true;
179 for (int i = 0; i < MAX_THREADS; i++)
181 // Wake up all the threads and waits for termination
184 threads[i].wake_up();
185 while (threads[i].state != Thread::TERMINATED) {}
188 // Now we can safely destroy the locks and wait conditions
189 lock_destroy(&threads[i].sleepLock);
190 cond_destroy(&threads[i].sleepCond);
192 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
193 lock_destroy(&(threads[i].splitPoints[j].lock));
196 lock_destroy(&threadsLock);
200 // init_hash_tables() dynamically allocates pawn and material hash tables
201 // according to the number of active threads. This avoids preallocating
202 // memory for all possible threads if only few are used as, for instance,
203 // on mobile devices where memory is scarce and allocating for MAX_THREADS
204 // threads could even result in a crash.
206 void ThreadsManager::init_hash_tables() {
208 for (int i = 0; i < activeThreads; i++)
210 threads[i].pawnTable.init();
211 threads[i].materialTable.init();
216 // available_slave_exists() tries to find an idle thread which is available as
217 // a slave for the thread with threadID "master".
219 bool ThreadsManager::available_slave_exists(int master) const {
221 assert(master >= 0 && master < activeThreads);
223 for (int i = 0; i < activeThreads; i++)
224 if (i != master && threads[i].is_available_to(master))
231 // split() does the actual work of distributing the work at a node between
232 // several available threads. If it does not succeed in splitting the
233 // node (because no idle threads are available, or because we have no unused
234 // split point objects), the function immediately returns. If splitting is
235 // possible, a SplitPoint object is initialized with all the data that must be
236 // copied to the helper threads and we tell our helper threads that they have
237 // been assigned work. This will cause them to instantly leave their idle loops and
238 // call search().When all threads have returned from search() then split() returns.
241 Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value beta,
242 Value bestValue, Depth depth, Move threatMove,
243 int moveCount, MovePicker* mp, int nodeType) {
245 assert(bestValue >= -VALUE_INFINITE);
246 assert(bestValue <= alpha);
247 assert(alpha < beta);
248 assert(beta <= VALUE_INFINITE);
249 assert(depth > DEPTH_ZERO);
250 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
251 assert(activeThreads > 1);
253 int i, master = pos.thread();
254 Thread& masterThread = threads[master];
256 // If we already have too many active split points, don't split
257 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
260 // Pick the next available split point object from the split point stack
261 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints];
263 // Initialize the split point object
264 splitPoint.parent = masterThread.splitPoint;
265 splitPoint.master = master;
266 splitPoint.is_betaCutoff = false;
267 splitPoint.depth = depth;
268 splitPoint.threatMove = threatMove;
269 splitPoint.alpha = alpha;
270 splitPoint.beta = beta;
271 splitPoint.nodeType = nodeType;
272 splitPoint.bestValue = bestValue;
274 splitPoint.moveCount = moveCount;
275 splitPoint.pos = &pos;
276 splitPoint.nodes = 0;
278 for (i = 0; i < activeThreads; i++)
279 splitPoint.is_slave[i] = false;
281 // If we are here it means we are not available
282 assert(masterThread.state == Thread::SEARCHING);
284 int workersCnt = 1; // At least the master is included
286 // Try to allocate available threads setting state to Thread::BOOKED, this
287 // must be done under lock protection to avoid concurrent allocation of
288 // the same slave by another master.
289 lock_grab(&threadsLock);
291 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
292 if (i != master && threads[i].is_available_to(master))
294 threads[i].state = Thread::BOOKED;
295 threads[i].splitPoint = &splitPoint;
296 splitPoint.is_slave[i] = true;
300 lock_release(&threadsLock);
302 // We failed to allocate even one slave, return
303 if (!Fake && workersCnt == 1)
306 masterThread.activeSplitPoints++;
307 masterThread.splitPoint = &splitPoint;
309 // Tell the threads that they have some work to do. This will make them leave
311 for (i = 0; i < activeThreads; i++)
312 if (i == master || splitPoint.is_slave[i])
314 assert(i == master || threads[i].state == Thread::BOOKED);
316 // This makes the slave to exit from idle_loop()
317 threads[i].state = Thread::WORKISWAITING;
319 if (useSleepingThreads && i != master)
320 threads[i].wake_up();
323 // Everything is set up. The master thread enters the idle loop, from
324 // which it will instantly launch a search, because its state is
325 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
326 // idle loop, which means that the main thread will return from the idle
327 // loop when all threads have finished their work at this split point.
328 idle_loop(master, &splitPoint);
330 // We have returned from the idle loop, which means that all threads are
331 // finished. Note that changing state and decreasing activeSplitPoints is done
332 // under lock protection to avoid a race with Thread::is_available_to().
333 lock_grab(&threadsLock);
335 masterThread.state = Thread::SEARCHING;
336 masterThread.activeSplitPoints--;
337 masterThread.splitPoint = splitPoint.parent;
339 lock_release(&threadsLock);
341 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
342 return splitPoint.bestValue;
345 // Explicit template instantiations
346 template Value ThreadsManager::split<false>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
347 template Value ThreadsManager::split<true>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);