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Get rid of timer thread

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Unfortunately std::condition_variable::wait_for()
is not accurate in general case and the timer thread
can wake up also after tens or even hundreds of
millisecs after time has elapsded. CPU load, process
priorities, number of concurrent threads, even from
other processes, will have effect upon it.

Even official documentation says: "This function may
block for longer than timeout_duration due to scheduling
or resource contention delays."

So retire timer and use a polling scheme based on a
local thread counter that counts search() calls and
a small trick to keep polling frequency constant,
independently from the number of threads.

Tested for no regression at very fast TC 2+0.05 th 7:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 32969 W: 6720 L: 6620 D: 19629

TC 2+0.05 th 1:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 7765 W: 1917 L: 1765 D: 4083

And at STC TC, both single thread
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 15587 W: 3036 L: 2905 D: 9646

And with 7 threads
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 8149 W: 1367 L: 1227 D: 5555

bench: 8639247
This commit is contained in:
Marco Costalba 2015-11-03 11:15:14 +01:00
parent 27c5cb5912
commit 9c9205860c
4 changed files with 66 additions and 91 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

95
src/search.cpp
View file

@ -141,6 +141,7 @@ namespace {
Value value_from_tt(Value v, int ply);
void update_pv(Move* pv, Move move, Move* childPv);
void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
void check_time();
} // namespace
@ -298,14 +299,10 @@ void MainThread::think() {
}
}
Threads.timer->run = true;
Threads.timer->notify_one(); // Start the recurring timer
search(true); // Let's start searching!
// Stop the threads and the timer
// Stop the threads
Signals.stop = true;
Threads.timer->run = false;
// Wait until all threads have finished
for (Thread* th : Threads)
@ -585,6 +582,20 @@ namespace {
bestValue = -VALUE_INFINITE;
ss->ply = (ss-1)->ply + 1;
// Check for available remaining time
if (thisThread->resetCallsCnt.load(std::memory_order_relaxed))
{
thisThread->resetCallsCnt = false;
thisThread->callsCnt = 0;
}
if (++thisThread->callsCnt > 4096)
{
for (Thread* th : Threads)
th->resetCallsCnt = true;
check_time();
}
// Used to send selDepth info to GUI
if (PvNode && thisThread->maxPly < ss->ply)
thisThread->maxPly = ss->ply;
@ -1455,6 +1466,43 @@ moves_loop: // When in check search starts from here
return best;
}
// check_time() is used to print debug info and, more importantly, to detect
// when we are out of available time and thus stop the search.
void check_time() {
static TimePoint lastInfoTime = now();
int elapsed = Time.elapsed();
TimePoint tick = Limits.startTime + elapsed;
if (tick - lastInfoTime >= 1000)
{
lastInfoTime = tick;
dbg_print();
}
// An engine may not stop pondering until told so by the GUI
if (Limits.ponder)
return;
if (Limits.use_time_management())
{
bool stillAtFirstMove = Signals.firstRootMove.load(std::memory_order_relaxed)
&& !Signals.failedLowAtRoot.load(std::memory_order_relaxed)
&& elapsed > Time.available() * 3 / 4;
if (stillAtFirstMove || elapsed > Time.maximum() - 10)
Signals.stop = true;
}
else if (Limits.movetime && elapsed >= Limits.movetime)
Signals.stop = true;
else if (Limits.nodes && Threads.nodes_searched() >= Limits.nodes)
Signals.stop = true;
}
} // namespace
@ -1565,40 +1613,3 @@ bool RootMove::extract_ponder_from_tt(Position& pos)
return false;
}
/// TimerThread::check_time() is called by when the timer triggers. It is used
/// to print debug info and, more importantly, to detect when we are out of
/// available time and thus stop the search.
void TimerThread::check_time() {
static TimePoint lastInfoTime = now();
int elapsed = Time.elapsed();
if (now() - lastInfoTime >= 1000)
{
lastInfoTime = now();
dbg_print();
}
// An engine may not stop pondering until told so by the GUI
if (Limits.ponder)
return;
if (Limits.use_time_management())
{
bool stillAtFirstMove = Signals.firstRootMove
&& !Signals.failedLowAtRoot
&& elapsed > Time.available() * 3 / 4;
if ( stillAtFirstMove
|| elapsed > Time.maximum() - 2 * TimerThread::Resolution)
Signals.stop = true;
}
else if (Limits.movetime && elapsed >= Limits.movetime)
Signals.stop = true;
else if (Limits.nodes && Threads.nodes_searched() >= Limits.nodes)
Signals.stop = true;
}

2
src/search.h
View file

@ -93,7 +93,7 @@ struct LimitsType {
/// typically in an async fashion e.g. to stop the search by the GUI.
struct SignalsType {
std::atomic<bool> stop, stopOnPonderhit, firstRootMove, failedLowAtRoot;
std::atomic_bool stop, stopOnPonderhit, firstRootMove, failedLowAtRoot;
};
typedef std::unique_ptr<std::stack<StateInfo>> StateStackPtr;

32
src/thread.cpp
View file

@ -66,7 +66,7 @@ void ThreadBase::notify_one() {
// ThreadBase::wait() set the thread to sleep until 'condition' turns true
void ThreadBase::wait(std::atomic<bool>& condition) {
void ThreadBase::wait(std::atomic_bool& condition) {
std::unique_lock<Mutex> lk(mutex);
sleepCondition.wait(lk, [&]{ return bool(condition); });
@ -74,7 +74,7 @@ void ThreadBase::wait(std::atomic<bool>& condition) {
// ThreadBase::wait_while() set the thread to sleep until 'condition' turns false
void ThreadBase::wait_while(std::atomic<bool>& condition) {
void ThreadBase::wait_while(std::atomic_bool& condition) {
std::unique_lock<Mutex> lk(mutex);
sleepCondition.wait(lk, [&]{ return !condition; });
@ -86,34 +86,14 @@ void ThreadBase::wait_while(std::atomic<bool>& condition) {
Thread::Thread() {
searching = false;
maxPly = 0;
searching = resetCallsCnt = false;
maxPly = callsCnt = 0;
history.clear();
counterMoves.clear();
idx = Threads.size(); // Starts from 0
}
// TimerThread::idle_loop() is where the timer thread waits Resolution milliseconds
// and then calls check_time(). When not searching, thread sleeps until it's woken up.
void TimerThread::idle_loop() {
while (!exit)
{
std::unique_lock<Mutex> lk(mutex);
if (!exit)
sleepCondition.wait_for(lk, std::chrono::milliseconds(run ? Resolution : INT_MAX));
lk.unlock();
if (!exit && run)
check_time();
}
}
// Thread::idle_loop() is where the thread is parked when it has no work to do
void Thread::idle_loop() {
@ -174,7 +154,6 @@ void MainThread::join() {
void ThreadPool::init() {
timer = new_thread<TimerThread>();
push_back(new_thread<MainThread>());
read_uci_options();
}
@ -185,9 +164,6 @@ void ThreadPool::init() {
void ThreadPool::exit() {
delete_thread(timer); // As first because check_time() accesses threads data
timer = nullptr;
for (Thread* th : *this)
delete_thread(th);

28
src/thread.h
View file

@ -44,12 +44,12 @@ struct ThreadBase : public std::thread {
virtual ~ThreadBase() = default;
virtual void idle_loop() = 0;
void notify_one();
void wait(std::atomic<bool>& b);
void wait_while(std::atomic<bool>& b);
void wait(std::atomic_bool& b);
void wait_while(std::atomic_bool& b);
Mutex mutex;
ConditionVariable sleepCondition;
std::atomic<bool> exit;
std::atomic_bool exit;
};
@ -68,8 +68,8 @@ struct Thread : public ThreadBase {
Material::Table materialTable;
Endgames endgames;
size_t idx, PVIdx;
int maxPly;
std::atomic<bool> searching;
int maxPly, callsCnt;
std::atomic_bool searching, resetCallsCnt;
Position rootPos;
Search::RootMoveVector rootMoves;
@ -80,25 +80,14 @@ struct Thread : public ThreadBase {
};
/// MainThread and TimerThread are derived classes used to characterize the two
/// special threads: the main one and the recurring timer.
/// MainThread is a derived classes used to characterize the the main one
struct MainThread : public Thread {
MainThread() { thinking = true; } // Avoid a race with start_thinking()
virtual void idle_loop();
void join();
void think();
std::atomic<bool> thinking;
};
struct TimerThread : public ThreadBase {
static const int Resolution = 5; // Millisec between two check_time() calls
virtual void idle_loop();
void check_time();
bool run = false;
std::atomic_bool thinking;
};
@ -108,14 +97,13 @@ struct TimerThread : public ThreadBase {
struct ThreadPool : public std::vector<Thread*> {
void init(); // No constructor and destructor, threads rely on globals that should
void init(); // No constructor and destructor, threads rely on globals that should
void exit(); // be initialized and valid during the whole thread lifetime.
MainThread* main() { return static_cast<MainThread*>(at(0)); }
void read_uci_options();
void start_thinking(const Position&, const Search::LimitsType&, Search::StateStackPtr&);
int64_t nodes_searched();
TimerThread* timer;
};
extern ThreadPool Threads;