/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see .
*/
#include
#include "thread.h"
#include "ucioption.h"
ThreadsManager ThreadsMgr; // Global object definition
namespace {
// init_thread() is the function which is called when a new thread is
// launched. It simply calls the idle_loop() function with the supplied
// threadID. There are two versions of this function; one for POSIX
// threads and one for Windows threads.
#if !defined(_MSC_VER)
void* init_thread(void* threadID) {
ThreadsMgr.idle_loop(*(int*)threadID, NULL);
return NULL;
}
#else
DWORD WINAPI init_thread(LPVOID threadID) {
ThreadsMgr.idle_loop(*(int*)threadID, NULL);
return 0;
}
#endif
}
// read_uci_options() updates number of active threads and other internal
// parameters according to the UCI options values. It is called before
// to start a new search.
void ThreadsManager::read_uci_options() {
maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value();
minimumSplitDepth = Options["Minimum Split Depth"].value() * ONE_PLY;
useSleepingThreads = Options["Use Sleeping Threads"].value();
activeThreads = Options["Threads"].value();
}
// init_threads() is called during startup. Initializes locks and condition
// variables and launches all threads sending them immediately to sleep.
void ThreadsManager::init_threads() {
int i, arg[MAX_THREADS];
bool ok;
// This flag is needed to properly end the threads when program exits
allThreadsShouldExit = false;
// Threads will sent to sleep as soon as created, only main thread is kept alive
activeThreads = 1;
lock_init(&mpLock);
for (i = 0; i < MAX_THREADS; i++)
{
// Initialize thread and split point locks
lock_init(&threads[i].sleepLock);
cond_init(&threads[i].sleepCond);
for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
lock_init(&(threads[i].splitPoints[j].lock));
// All threads but first should be set to THREAD_INITIALIZING
threads[i].state = (i == 0 ? THREAD_SEARCHING : THREAD_INITIALIZING);
// Not in Threads c'tor to avoid global initialization order issues
threads[i].pawnTable.init();
threads[i].materialTable.init();
}
// Create and startup the threads
for (i = 1; i < MAX_THREADS; i++)
{
arg[i] = i;
#if !defined(_MSC_VER)
pthread_t pthread[1];
ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
pthread_detach(pthread[0]);
#else
ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
#endif
if (!ok)
{
std::cout << "Failed to create thread number " << i << std::endl;
exit(EXIT_FAILURE);
}
// Wait until the thread has finished launching and is gone to sleep
while (threads[i].state == THREAD_INITIALIZING) {}
}
}
// exit_threads() is called when the program exits. It makes all the
// helper threads exit cleanly.
void ThreadsManager::exit_threads() {
// Force the woken up threads to exit idle_loop() and hence terminate
allThreadsShouldExit = true;
for (int i = 0; i < MAX_THREADS; i++)
{
// Wake up all the threads and waits for termination
if (i != 0)
{
threads[i].wake_up();
while (threads[i].state != THREAD_TERMINATED) {}
}
// Now we can safely destroy the locks and wait conditions
lock_destroy(&threads[i].sleepLock);
cond_destroy(&threads[i].sleepCond);
for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
lock_destroy(&(threads[i].splitPoints[j].lock));
}
lock_destroy(&mpLock);
}
// cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
// the thread's currently active split point, or in some ancestor of
// the current split point.
bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
assert(threadID >= 0 && threadID < activeThreads);
SplitPoint* sp = threads[threadID].splitPoint;
for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
return sp != NULL;
}
// thread_is_available() checks whether the thread with threadID "slave" is
// available to help the thread with threadID "master" at a split point. An
// obvious requirement is that "slave" must be idle. With more than two
// threads, this is not by itself sufficient: If "slave" is the master of
// some active split point, it is only available as a slave to the other
// threads which are busy searching the split point at the top of "slave"'s
// split point stack (the "helpful master concept" in YBWC terminology).
bool ThreadsManager::thread_is_available(int slave, int master) const {
assert(slave >= 0 && slave < activeThreads);
assert(master >= 0 && master < activeThreads);
assert(activeThreads > 1);
if (threads[slave].state != THREAD_AVAILABLE || slave == master)
return false;
// Make a local copy to be sure doesn't change under our feet
int localActiveSplitPoints = threads[slave].activeSplitPoints;
// No active split points means that the thread is available as
// a slave for any other thread.
if (localActiveSplitPoints == 0 || activeThreads == 2)
return true;
// Apply the "helpful master" concept if possible. Use localActiveSplitPoints
// that is known to be > 0, instead of threads[slave].activeSplitPoints that
// could have been set to 0 by another thread leading to an out of bound access.
if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
return true;
return false;
}
// available_thread_exists() tries to find an idle thread which is available as
// a slave for the thread with threadID "master".
bool ThreadsManager::available_thread_exists(int master) const {
assert(master >= 0 && master < activeThreads);
assert(activeThreads > 1);
for (int i = 0; i < activeThreads; i++)
if (thread_is_available(i, master))
return true;
return false;
}
// split() does the actual work of distributing the work at a node between
// several available threads. If it does not succeed in splitting the
// node (because no idle threads are available, or because we have no unused
// split point objects), the function immediately returns. If splitting is
// possible, a SplitPoint object is initialized with all the data that must be
// copied to the helper threads and we tell our helper threads that they have
// been assigned work. This will cause them to instantly leave their idle loops and
// call search().When all threads have returned from search() then split() returns.
template
void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const Value beta,
Value* bestValue, Depth depth, Move threatMove,
int moveCount, MovePicker* mp, bool pvNode) {
assert(pos.is_ok());
assert(*bestValue >= -VALUE_INFINITE);
assert(*bestValue <= *alpha);
assert(*alpha < beta);
assert(beta <= VALUE_INFINITE);
assert(depth > DEPTH_ZERO);
assert(pos.thread() >= 0 && pos.thread() < activeThreads);
assert(activeThreads > 1);
int i, master = pos.thread();
Thread& masterThread = threads[master];
lock_grab(&mpLock);
// If no other thread is available to help us, or if we have too many
// active split points, don't split.
if ( !available_thread_exists(master)
|| masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
{
lock_release(&mpLock);
return;
}
// Pick the next available split point object from the split point stack
SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
// Initialize the split point object
splitPoint.parent = masterThread.splitPoint;
splitPoint.master = master;
splitPoint.betaCutoff = false;
splitPoint.depth = depth;
splitPoint.threatMove = threatMove;
splitPoint.alpha = *alpha;
splitPoint.beta = beta;
splitPoint.pvNode = pvNode;
splitPoint.bestValue = *bestValue;
splitPoint.mp = mp;
splitPoint.moveCount = moveCount;
splitPoint.pos = &pos;
splitPoint.nodes = 0;
splitPoint.ss = ss;
for (i = 0; i < activeThreads; i++)
splitPoint.slaves[i] = 0;
masterThread.splitPoint = &splitPoint;
// If we are here it means we are not available
assert(masterThread.state != THREAD_AVAILABLE);
int workersCnt = 1; // At least the master is included
// Allocate available threads setting state to THREAD_BOOKED
for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
if (thread_is_available(i, master))
{
threads[i].state = THREAD_BOOKED;
threads[i].splitPoint = &splitPoint;
splitPoint.slaves[i] = 1;
workersCnt++;
}
assert(Fake || workersCnt > 1);
// We can release the lock because slave threads are already booked and master is not available
lock_release(&mpLock);
// Tell the threads that they have work to do. This will make them leave
// their idle loop.
for (i = 0; i < activeThreads; i++)
if (i == master || splitPoint.slaves[i])
{
assert(i == master || threads[i].state == THREAD_BOOKED);
threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
if (useSleepingThreads && i != master)
threads[i].wake_up();
}
// Everything is set up. The master thread enters the idle loop, from
// which it will instantly launch a search, because its state is
// THREAD_WORKISWAITING. We send the split point as a second parameter to the
// idle loop, which means that the main thread will return from the idle
// loop when all threads have finished their work at this split point.
idle_loop(master, &splitPoint);
// We have returned from the idle loop, which means that all threads are
// finished. Update alpha and bestValue, and return.
lock_grab(&mpLock);
*alpha = splitPoint.alpha;
*bestValue = splitPoint.bestValue;
masterThread.activeSplitPoints--;
masterThread.splitPoint = splitPoint.parent;
pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
lock_release(&mpLock);
}
// Explicit template instantiations
template void ThreadsManager::split<0>(Position&, SearchStack*, Value*, const Value, Value*, Depth, Move, int, MovePicker*, bool);
template void ThreadsManager::split<1>(Position&, SearchStack*, Value*, const Value, Value*, Depth, Move, int, MovePicker*, bool);