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thread.cpp
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thread.cpp
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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2013 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 <http://www.gnu.org/licenses/>.
*/
#include <algorithm> // For std::count
#include <cassert>
#include "movegen.h"
#include "search.h"
#include "thread.h"
#include "ucioption.h"
using namespace Search;
ThreadPool Threads; // Global object
namespace {
// start_routine() is the C function which is called when a new thread
// is launched. It is a wrapper to the virtual function idle_loop().
extern "C" { long start_routine(ThreadBase* th) { th->idle_loop(); return 0; } }
// Helpers to launch a thread after creation and joining before delete. Must be
// outside Thread c'tor and d'tor because object shall be fully initialized
// when start_routine (and hence virtual idle_loop) is called and when joining.
template<typename T> T* new_thread() {
T* th = new T();
thread_create(th->handle, start_routine, th); // Will go to sleep
return th;
}
void delete_thread(ThreadBase* th) {
th->exit = true; // Search must be already finished
th->notify_one();
thread_join(th->handle); // Wait for thread termination
delete th;
}
}
// ThreadBase::notify_one() wakes up the thread when there is some work to do
void ThreadBase::notify_one() {
mutex.lock();
sleepCondition.notify_one();
mutex.unlock();
}
// ThreadBase::wait_for() set the thread to sleep until condition 'b' turns true
void ThreadBase::wait_for(volatile const bool& b) {
mutex.lock();
while (!b) sleepCondition.wait(mutex);
mutex.unlock();
}
// Thread c'tor just inits data but does not launch any thread of execution that
// instead will be started only upon c'tor returns.
Thread::Thread() /* : splitPoints() */ { // Value-initialization bug in MSVC
searching = false;
maxPly = splitPointsSize = 0;
activeSplitPoint = NULL;
activePosition = NULL;
idx = Threads.size();
}
// TimerThread::idle_loop() is where the timer thread waits msec milliseconds
// and then calls check_time(). If msec is 0 thread sleeps until is woken up.
extern void check_time();
void TimerThread::idle_loop() {
while (!exit)
{
mutex.lock();
if (!exit)
sleepCondition.wait_for(mutex, msec ? msec : INT_MAX);
mutex.unlock();
if (msec)
check_time();
}
}
// MainThread::idle_loop() is where the main thread is parked waiting to be started
// when there is a new search. Main thread will launch all the slave threads.
void MainThread::idle_loop() {
while (true)
{
mutex.lock();
thinking = false;
while (!thinking && !exit)
{
Threads.sleepCondition.notify_one(); // Wake up UI thread if needed
sleepCondition.wait(mutex);
}
mutex.unlock();
if (exit)
return;
searching = true;
Search::think();
assert(searching);
searching = false;
}
}
// Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
// current active split point, or in some ancestor of the split point.
bool Thread::cutoff_occurred() const {
for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parentSplitPoint)
if (sp->cutoff)
return true;
return false;
}
// Thread::available_to() checks whether the thread is available to help the
// thread 'master' at a split point. An obvious requirement is that thread must
// be idle. With more than two threads, this is not sufficient: If the thread is
// the master of some split point, it is only available as a slave to the slaves
// which are busy searching the split point at the top of slaves split point
// stack (the "helpful master concept" in YBWC terminology).
bool Thread::available_to(const Thread* master) const {
if (searching)
return false;
// Make a local copy to be sure doesn't become zero under our feet while
// testing next condition and so leading to an out of bound access.
int size = splitPointsSize;
// No split points means that the thread is available as a slave for any
// other thread otherwise apply the "helpful master" concept if possible.
return !size || (splitPoints[size - 1].slavesMask & (1ULL << master->idx));
}
// init() is called at startup to create and launch requested threads, that will
// go immediately to sleep due to 'sleepWhileIdle' set to true. We cannot use
// a c'tor becuase Threads is a static object and we need a fully initialized
// engine at this point due to allocation of Endgames in Thread c'tor.
void ThreadPool::init() {
sleepWhileIdle = true;
timer = new_thread<TimerThread>();
push_back(new_thread<MainThread>());
read_uci_options();
}
// exit() cleanly terminates the threads before the program exits
void ThreadPool::exit() {
delete_thread(timer); // As first because check_time() accesses threads data
for (iterator it = begin(); it != end(); ++it)
delete_thread(*it);
}
// read_uci_options() updates internal threads parameters from the corresponding
// UCI options and creates/destroys threads to match the requested number. Thread
// objects are dynamically allocated to avoid creating in advance all possible
// threads, with included pawns and material tables, if only few are used.
void ThreadPool::read_uci_options() {
maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
size_t requested = Options["Threads"];
assert(requested > 0);
// Value 0 has a special meaning: We determine the optimal minimum split depth
// automatically. Anyhow the minimumSplitDepth should never be under 4 plies.
if (!minimumSplitDepth)
minimumSplitDepth = (requested < 8 ? 4 : 7) * ONE_PLY;
else
minimumSplitDepth = std::max(4 * ONE_PLY, minimumSplitDepth);
while (size() < requested)
push_back(new_thread<Thread>());
while (size() > requested)
{
delete_thread(back());
pop_back();
}
}
// slave_available() tries to find an idle thread which is available as a slave
// for the thread 'master'.
Thread* ThreadPool::available_slave(const Thread* master) const {
for (const_iterator it = begin(); it != end(); ++it)
if ((*it)->available_to(master))
return *it;
return NULL;
}
// 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), 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 then helper threads are
// told 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 <bool Fake>
void Thread::split(Position& pos, const Stack* ss, Value alpha, Value beta, Value* bestValue,
Move* bestMove, Depth depth, Move threatMove, int moveCount,
MovePicker* movePicker, int nodeType, bool cutNode) {
assert(pos.pos_is_ok());
assert(*bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(*bestValue > -VALUE_INFINITE);
assert(depth >= Threads.minimumSplitDepth);
assert(searching);
assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
// Pick the next available split point from the split point stack
SplitPoint& sp = splitPoints[splitPointsSize];
sp.masterThread = this;
sp.parentSplitPoint = activeSplitPoint;
sp.slavesMask = 1ULL << idx;
sp.depth = depth;
sp.bestValue = *bestValue;
sp.bestMove = *bestMove;
sp.threatMove = threatMove;
sp.alpha = alpha;
sp.beta = beta;
sp.nodeType = nodeType;
sp.cutNode = cutNode;
sp.movePicker = movePicker;
sp.moveCount = moveCount;
sp.pos = &pos;
sp.nodes = 0;
sp.cutoff = false;
sp.ss = ss;
// Try to allocate available threads and ask them to start searching setting
// 'searching' flag. This must be done under lock protection to avoid concurrent
// allocation of the same slave by another master.
Threads.mutex.lock();
sp.mutex.lock();
++splitPointsSize;
activeSplitPoint = &sp;
activePosition = NULL;
size_t slavesCnt = 1; // This thread is always included
Thread* slave;
while ( (slave = Threads.available_slave(this)) != NULL
&& ++slavesCnt <= Threads.maxThreadsPerSplitPoint && !Fake)
{
sp.slavesMask |= 1ULL << slave->idx;
slave->activeSplitPoint = &sp;
slave->searching = true; // Slave leaves idle_loop()
slave->notify_one(); // Could be sleeping
}
// Everything is set up. The master thread enters the idle loop, from which
// it will instantly launch a search, because its 'searching' flag is set.
// The thread will return from the idle loop when all slaves have finished
// their work at this split point.
if (slavesCnt > 1 || Fake)
{
sp.mutex.unlock();
Threads.mutex.unlock();
Thread::idle_loop(); // Force a call to base class idle_loop()
// In helpful master concept a master can help only a sub-tree of its split
// point, and because here is all finished is not possible master is booked.
assert(!searching);
assert(!activePosition);
// We have returned from the idle loop, which means that all threads are
// finished. Note that setting 'searching' and decreasing splitPointsSize is
// done under lock protection to avoid a race with Thread::available_to().
Threads.mutex.lock();
sp.mutex.lock();
}
searching = true;
--splitPointsSize;
activeSplitPoint = sp.parentSplitPoint;
activePosition = &pos;
pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
*bestMove = sp.bestMove;
*bestValue = sp.bestValue;
sp.mutex.unlock();
Threads.mutex.unlock();
}
// Explicit template instantiations
template void Thread::split<false>(Position&, const Stack*, Value, Value, Value*, Move*, Depth, Move, int, MovePicker*, int, bool);
template void Thread::split< true>(Position&, const Stack*, Value, Value, Value*, Move*, Depth, Move, int, MovePicker*, int, bool);
// wait_for_think_finished() waits for main thread to go to sleep then returns
void ThreadPool::wait_for_think_finished() {
MainThread* t = main();
t->mutex.lock();
while (t->thinking) sleepCondition.wait(t->mutex);
t->mutex.unlock();
}
// start_thinking() wakes up the main thread sleeping in MainThread::idle_loop()
// so to start a new search, then returns immediately.
void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
const std::vector<Move>& searchMoves, StateStackPtr& states) {
wait_for_think_finished();
Time::processTime = Options["ProcessTime"];
SearchTime = Time::now(); // As early as possible
Signals.stopOnPonderhit = Signals.firstRootMove = false;
Signals.stop = Signals.failedLowAtRoot = false;
RootMoves.clear();
RootPos = pos;
Limits = limits;
if (states.get()) // If we don't set a new position, preserve current state
{
SetupStates = states; // Ownership transfer here
assert(!states.get());
}
for (MoveList<LEGAL> it(pos); *it; ++it)
if ( searchMoves.empty()
|| std::count(searchMoves.begin(), searchMoves.end(), *it))
RootMoves.push_back(RootMove(*it));
main()->thinking = true;
main()->notify_one(); // Starts main thread
}