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 // Initialize threads lock, used when allocating slaves during splitting
136 lock_init(&threadsLock);
138 // Initialize sleep and split point locks
139 for (int i = 0; i < MAX_THREADS; i++)
141 lock_init(&threads[i].sleepLock);
142 cond_init(&threads[i].sleepCond);
144 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
145 lock_init(&(threads[i].splitPoints[j].lock));
148 // Create and startup all the threads but the main that is already running
149 for (int i = 1; i < MAX_THREADS; i++)
151 threads[i].state = Thread::INITIALIZING;
154 #if defined(_MSC_VER)
155 bool ok = (CreateThread(NULL, 0, start_routine, (LPVOID)&threadID[i], 0, NULL) != NULL);
158 bool ok = (pthread_create(&pthreadID, NULL, start_routine, (void*)&threadID[i]) == 0);
159 pthread_detach(pthreadID);
163 std::cout << "Failed to create thread number " << i << std::endl;
164 ::exit(EXIT_FAILURE);
167 // Wait until the thread has finished launching and is gone to sleep
168 while (threads[i].state == Thread::INITIALIZING) {}
173 // exit() is called to cleanly terminate the threads when the program finishes
175 void ThreadsManager::exit() {
177 // Force the woken up threads to exit idle_loop() and hence terminate
178 allThreadsShouldExit = true;
180 for (int i = 0; i < MAX_THREADS; i++)
182 // Wake up all the threads and wait for termination
185 threads[i].wake_up();
186 while (threads[i].state != Thread::TERMINATED) {}
189 // Now we can safely destroy locks and wait conditions
190 lock_destroy(&threads[i].sleepLock);
191 cond_destroy(&threads[i].sleepCond);
193 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
194 lock_destroy(&(threads[i].splitPoints[j].lock));
197 lock_destroy(&threadsLock);
201 // init_hash_tables() dynamically allocates pawn and material hash tables
202 // according to the number of active threads. This avoids preallocating
203 // memory for all possible threads if only few are used as, for instance,
204 // on mobile devices where memory is scarce and allocating for MAX_THREADS
205 // threads could even result in a crash.
207 void ThreadsManager::init_hash_tables() {
209 for (int i = 0; i < activeThreads; i++)
211 threads[i].pawnTable.init();
212 threads[i].materialTable.init();
217 // available_slave_exists() tries to find an idle thread which is available as
218 // a slave for the thread with threadID "master".
220 bool ThreadsManager::available_slave_exists(int master) const {
222 assert(master >= 0 && master < activeThreads);
224 for (int i = 0; i < activeThreads; i++)
225 if (i != master && threads[i].is_available_to(master))
232 // split() does the actual work of distributing the work at a node between
233 // several available threads. If it does not succeed in splitting the
234 // node (because no idle threads are available, or because we have no unused
235 // split point objects), the function immediately returns. If splitting is
236 // possible, a SplitPoint object is initialized with all the data that must be
237 // copied to the helper threads and we tell our helper threads that they have
238 // been assigned work. This will cause them to instantly leave their idle loops and
239 // call search().When all threads have returned from search() then split() returns.
242 Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value beta,
243 Value bestValue, Depth depth, Move threatMove,
244 int moveCount, MovePicker* mp, int nodeType) {
246 assert(bestValue >= -VALUE_INFINITE);
247 assert(bestValue <= alpha);
248 assert(alpha < beta);
249 assert(beta <= VALUE_INFINITE);
250 assert(depth > DEPTH_ZERO);
251 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
252 assert(activeThreads > 1);
254 int i, master = pos.thread();
255 Thread& masterThread = threads[master];
257 // If we already have too many active split points, don't split
258 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
261 // Pick the next available split point object from the split point stack
262 SplitPoint* sp = masterThread.splitPoints + masterThread.activeSplitPoints;
264 // Initialize the split point object
265 sp->parent = masterThread.splitPoint;
267 sp->is_betaCutoff = false;
269 sp->threatMove = threatMove;
272 sp->nodeType = nodeType;
273 sp->bestValue = bestValue;
275 sp->moveCount = moveCount;
279 for (i = 0; i < activeThreads; i++)
280 sp->is_slave[i] = false;
282 // If we are here it means we are not available
283 assert(masterThread.state == Thread::SEARCHING);
285 int workersCnt = 1; // At least the master is included
287 // Try to allocate available threads and ask them to start searching setting
288 // the state to Thread::WORKISWAITING, this must be done under lock protection
289 // to avoid concurrent allocation of the same slave by another master.
290 lock_grab(&threadsLock);
292 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
293 if (i != master && threads[i].is_available_to(master))
296 sp->is_slave[i] = true;
297 threads[i].splitPoint = sp;
299 // This makes the slave to exit from idle_loop()
300 threads[i].state = Thread::WORKISWAITING;
302 if (useSleepingThreads)
303 threads[i].wake_up();
306 lock_release(&threadsLock);
308 // We failed to allocate even one slave, return
309 if (!Fake && workersCnt == 1)
312 masterThread.splitPoint = sp;
313 masterThread.activeSplitPoints++;
314 masterThread.state = Thread::WORKISWAITING;
316 // Everything is set up. The master thread enters the idle loop, from
317 // which it will instantly launch a search, because its state is
318 // Thread::WORKISWAITING. We send the split point as a second parameter to
319 // the idle loop, which means that the main thread will return from the idle
320 // loop when all threads have finished their work at this split point.
321 idle_loop(master, sp);
323 // In helpful master concept a master can help only a sub-tree, and
324 // because here is all finished is not possible master is booked.
325 assert(masterThread.state == Thread::AVAILABLE);
327 // We have returned from the idle loop, which means that all threads are
328 // finished. Note that changing state and decreasing activeSplitPoints is done
329 // under lock protection to avoid a race with Thread::is_available_to().
330 lock_grab(&threadsLock);
332 masterThread.state = Thread::SEARCHING;
333 masterThread.activeSplitPoints--;
335 lock_release(&threadsLock);
337 masterThread.splitPoint = sp->parent;
338 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
340 return sp->bestValue;
343 // Explicit template instantiations
344 template Value ThreadsManager::split<false>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
345 template Value ThreadsManager::split<true>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);