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[*(int*)threadID].idle_loop(NULL);
44 void* start_routine(void* threadID) {
46 Threads[*(int*)threadID].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
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>();
115 set_size(Options["Threads"].value<int>());
119 // set_size() changes the number of active threads and raises do_sleep flag for
120 // all the unused threads that will go immediately to sleep.
122 void ThreadsManager::set_size(int cnt) {
124 assert(cnt > 0 && cnt <= MAX_THREADS);
128 for (int i = 0; i < MAX_THREADS; i++)
129 threads[i].do_sleep = !(i < activeThreads);
133 // init() is called during startup. Initializes locks and condition variables
134 // and launches all threads sending them immediately to sleep.
136 void ThreadsManager::init() {
138 // Threads will go to sleep as soon as created, only main thread is kept alive
140 threads[0].state = Thread::SEARCHING;
141 threads[0].threadID = 0;
143 // Allocate pawn and material hash tables for main thread
146 // Initialize threads lock, used when allocating slaves during splitting
147 lock_init(&threadsLock);
149 // Initialize sleep and split point locks
150 for (int i = 0; i < MAX_THREADS; i++)
152 lock_init(&threads[i].sleepLock);
153 cond_init(&threads[i].sleepCond);
155 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
156 lock_init(&(threads[i].splitPoints[j].lock));
159 // Create and startup all the threads but the main that is already running
160 for (int i = 1; i < MAX_THREADS; i++)
162 threads[i].state = Thread::AVAILABLE;
163 threads[i].threadID = i;
165 #if defined(_MSC_VER)
166 threads[i].handle = CreateThread(NULL, 0, start_routine, (LPVOID)&threads[i].threadID, 0, NULL);
167 bool ok = (threads[i].handle != NULL);
169 bool ok = (pthread_create(&threads[i].handle, NULL, start_routine, (void*)&threads[i].threadID) == 0);
174 std::cout << "Failed to create thread number " << i << std::endl;
175 ::exit(EXIT_FAILURE);
181 // exit() is called to cleanly terminate the threads when the program finishes
183 void ThreadsManager::exit() {
185 for (int i = 0; i < MAX_THREADS; i++)
187 // Wake up all the slave threads and wait for termination
190 threads[i].do_terminate = true;
191 threads[i].wake_up();
193 #if defined(_MSC_VER)
194 WaitForSingleObject(threads[i].handle, 0);
195 CloseHandle(threads[i].handle);
197 pthread_join(threads[i].handle, NULL);
198 pthread_detach(threads[i].handle);
202 // Now we can safely destroy locks and wait conditions
203 lock_destroy(&threads[i].sleepLock);
204 cond_destroy(&threads[i].sleepCond);
206 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
207 lock_destroy(&(threads[i].splitPoints[j].lock));
210 lock_destroy(&threadsLock);
214 // init_hash_tables() dynamically allocates pawn and material hash tables
215 // according to the number of active threads. This avoids preallocating
216 // memory for all possible threads if only few are used as, for instance,
217 // on mobile devices where memory is scarce and allocating for MAX_THREADS
218 // threads could even result in a crash.
220 void ThreadsManager::init_hash_tables() {
222 for (int i = 0; i < activeThreads; i++)
224 threads[i].pawnTable.init();
225 threads[i].materialTable.init();
230 // available_slave_exists() tries to find an idle thread which is available as
231 // a slave for the thread with threadID "master".
233 bool ThreadsManager::available_slave_exists(int master) const {
235 assert(master >= 0 && master < activeThreads);
237 for (int i = 0; i < activeThreads; i++)
238 if (i != master && threads[i].is_available_to(master))
245 // split() does the actual work of distributing the work at a node between
246 // several available threads. If it does not succeed in splitting the
247 // node (because no idle threads are available, or because we have no unused
248 // split point objects), the function immediately returns. If splitting is
249 // possible, a SplitPoint object is initialized with all the data that must be
250 // copied to the helper threads and we tell our helper threads that they have
251 // been assigned work. This will cause them to instantly leave their idle loops and
252 // call search().When all threads have returned from search() then split() returns.
255 Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value beta,
256 Value bestValue, Depth depth, Move threatMove,
257 int moveCount, MovePicker* mp, int nodeType) {
259 assert(bestValue >= -VALUE_INFINITE);
260 assert(bestValue <= alpha);
261 assert(alpha < beta);
262 assert(beta <= VALUE_INFINITE);
263 assert(depth > DEPTH_ZERO);
264 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
265 assert(activeThreads > 1);
267 int i, master = pos.thread();
268 Thread& masterThread = threads[master];
270 // If we already have too many active split points, don't split
271 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
274 // Pick the next available split point object from the split point stack
275 SplitPoint* sp = masterThread.splitPoints + masterThread.activeSplitPoints;
277 // Initialize the split point object
278 sp->parent = masterThread.splitPoint;
280 sp->is_betaCutoff = false;
282 sp->threatMove = threatMove;
285 sp->nodeType = nodeType;
286 sp->bestValue = bestValue;
288 sp->moveCount = moveCount;
292 for (i = 0; i < activeThreads; i++)
293 sp->is_slave[i] = false;
295 // If we are here it means we are not available
296 assert(masterThread.state == Thread::SEARCHING);
298 int workersCnt = 1; // At least the master is included
300 // Try to allocate available threads and ask them to start searching setting
301 // the state to Thread::WORKISWAITING, this must be done under lock protection
302 // to avoid concurrent allocation of the same slave by another master.
303 lock_grab(&threadsLock);
305 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
306 if (i != master && threads[i].is_available_to(master))
309 sp->is_slave[i] = true;
310 threads[i].splitPoint = sp;
312 // This makes the slave to exit from idle_loop()
313 threads[i].state = Thread::WORKISWAITING;
315 if (useSleepingThreads)
316 threads[i].wake_up();
319 lock_release(&threadsLock);
321 // We failed to allocate even one slave, return
322 if (!Fake && workersCnt == 1)
325 masterThread.splitPoint = sp;
326 masterThread.activeSplitPoints++;
327 masterThread.state = Thread::WORKISWAITING;
329 // Everything is set up. The master thread enters the idle loop, from
330 // which it will instantly launch a search, because its state is
331 // Thread::WORKISWAITING. We send the split point as a second parameter to
332 // the idle loop, which means that the main thread will return from the idle
333 // loop when all threads have finished their work at this split point.
334 masterThread.idle_loop(sp);
336 // In helpful master concept a master can help only a sub-tree, and
337 // because here is all finished is not possible master is booked.
338 assert(masterThread.state == Thread::AVAILABLE);
340 // We have returned from the idle loop, which means that all threads are
341 // finished. Note that changing state and decreasing activeSplitPoints is done
342 // under lock protection to avoid a race with Thread::is_available_to().
343 lock_grab(&threadsLock);
345 masterThread.state = Thread::SEARCHING;
346 masterThread.activeSplitPoints--;
348 lock_release(&threadsLock);
350 masterThread.splitPoint = sp->parent;
351 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
353 return sp->bestValue;
356 // Explicit template instantiations
357 template Value ThreadsManager::split<false>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
358 template Value ThreadsManager::split<true>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);