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Fix comments in thread.cpp
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And reshuffle a bit the functions to place
them in a consistent order.

To be on the safe side, patch has been
validated for no regression/crashes with
a small 8K games test with 3 threads:

ELO: 3.98 +-4.4 (95%) LOS: 96.3%
Total: 8388 W: 1500 L: 1404 D: 5484

No functional change.
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@mcostalba
mcostalba committed Jan 3, 2015
1 parent 91cc82a commit 62f5312
Showing 1 changed file with 131 additions and 125 deletions.
256 changes: 131 additions & 125 deletions src/thread.cpp
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Expand Up @@ -40,7 +40,7 @@ namespace {


// Helpers to launch a thread after creation and joining before delete. Must be
// outside Thread c'tor and d'tor because the object will be fully initialized
// outside Thread c'tor and d'tor because the object must be fully initialized
// when start_routine (and hence virtual idle_loop) is called and when joining.

template<typename T> T* new_thread() {
Expand All @@ -50,7 +50,11 @@ namespace {
}

void delete_thread(ThreadBase* th) {

th->mutex.lock();
th->exit = true; // Search must be already finished
th->mutex.unlock();

th->notify_one();
thread_join(th->handle); // Wait for thread termination
delete th;
Expand All @@ -59,7 +63,7 @@ namespace {
}


// notify_one() wakes up the thread when there is some work to do
// ThreadBase::notify_one() wakes up the thread when there is some work to do

void ThreadBase::notify_one() {

Expand All @@ -69,7 +73,7 @@ void ThreadBase::notify_one() {
}


// wait_for() set the thread to sleep until 'condition' turns true
// ThreadBase::wait_for() set the thread to sleep until 'condition' turns true

void ThreadBase::wait_for(volatile const bool& condition) {

Expand All @@ -79,8 +83,8 @@ void ThreadBase::wait_for(volatile const bool& condition) {
}


// Thread c'tor just inits data and does not launch any execution thread.
// Such a thread will only be started when c'tor returns.
// Thread c'tor makes some init but does not launch any execution thread that
// will be started only when c'tor returns.

Thread::Thread() /* : splitPoints() */ { // Value-initialization bug in MSVC

Expand All @@ -92,7 +96,7 @@ Thread::Thread() /* : splitPoints() */ { // Value-initialization bug in MSVC
}


// cutoff_occurred() checks whether a beta cutoff has occurred in the
// 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 {
Expand Down Expand Up @@ -127,8 +131,101 @@ bool Thread::available_to(const Thread* master) const {
}


// TimerThread::idle_loop() is where the timer thread waits msec milliseconds
// and then calls check_time(). If msec is 0 thread sleeps until it's woken up.
// Thread::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
// informed 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.

void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bestValue,
Move* bestMove, Depth depth, int moveCount,
MovePicker* movePicker, int nodeType, bool cutNode) {

assert(searching);
assert(-VALUE_INFINITE < *bestValue && *bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(depth >= Threads.minimumSplitDepth);
assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);

// Pick and init the next available split point
SplitPoint& sp = splitPoints[splitPointsSize];

sp.masterThread = this;
sp.parentSplitPoint = activeSplitPoint;
sp.slavesMask = 0, sp.slavesMask.set(idx);
sp.depth = depth;
sp.bestValue = *bestValue;
sp.bestMove = *bestMove;
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();

sp.allSlavesSearching = true; // Must be set under lock protection
++splitPointsSize;
activeSplitPoint = &sp;
activePosition = NULL;

Thread* slave;

while ((slave = Threads.available_slave(this)) != NULL)
{
sp.slavesMask.set(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.
sp.mutex.unlock();
Threads.mutex.unlock();

Thread::idle_loop(); // Force a call to base class idle_loop()

// In the helpful master concept, a master can help only a sub-tree of its
// split point and because everything is finished here, it's not possible
// for the master to be 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 must
// be 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();
}


// 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() {

Expand All @@ -152,7 +249,7 @@ void TimerThread::idle_loop() {

void MainThread::idle_loop() {

while (true)
while (!exit)
{
mutex.lock();

Expand All @@ -166,24 +263,24 @@ void MainThread::idle_loop() {

mutex.unlock();

if (exit)
return;

searching = true;
if (!exit)
{
searching = true;

Search::think();
Search::think();

assert(searching);
assert(searching);

searching = false;
searching = false;
}
}
}


// init() is called at startup to create and launch requested threads, that will
// go immediately to sleep. We cannot use a c'tor because Threads is a static
// object and we need a fully initialized engine at this point due to allocation
// of Endgames in Thread c'tor.
// ThreadPool::init() is called at startup to create and launch requested threads,
// that will go immediately to sleep. We cannot use a c'tor because 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() {

Expand All @@ -193,8 +290,8 @@ void ThreadPool::init() {
}


// exit() cleanly terminates the threads before the program exits. Cannot be done in
// d'tor because we have to terminate the threads before to free ThreadPool object.
// ThreadPool::exit() terminates the threads before the program exits. Cannot be
// done in d'tor because threads must be terminated before freeing us.

void ThreadPool::exit() {

Expand All @@ -205,11 +302,11 @@ void ThreadPool::exit() {
}


// 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 all possible threads
// in advance (which include pawns and material tables), even if only a few
// are to be used.
// ThreadPool::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 all possible
// threads in advance (which include pawns and material tables), even if only a
// few are to be used.

void ThreadPool::read_uci_options() {

Expand All @@ -233,8 +330,8 @@ void ThreadPool::read_uci_options() {
}


// available_slave() tries to find an idle thread which is available as a slave
// for the thread 'master'.
// ThreadPool::available_slave() tries to find an idle thread which is available
// as a slave for the thread 'master'.

Thread* ThreadPool::available_slave(const Thread* master) const {

Expand All @@ -246,98 +343,7 @@ Thread* ThreadPool::available_slave(const Thread* master) const {
}


// 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.

void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bestValue,
Move* bestMove, Depth depth, int moveCount,
MovePicker* movePicker, int nodeType, bool cutNode) {

assert(pos.pos_is_ok());
assert(-VALUE_INFINITE < *bestValue && *bestValue <= alpha && alpha < beta && beta <= 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 = 0, sp.slavesMask.set(idx);
sp.depth = depth;
sp.bestValue = *bestValue;
sp.bestMove = *bestMove;
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();

sp.allSlavesSearching = true; // Must be set under lock protection
++splitPointsSize;
activeSplitPoint = &sp;
activePosition = NULL;

for (Thread* slave; (slave = Threads.available_slave(this)) != NULL; )
{
sp.slavesMask.set(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.
sp.mutex.unlock();
Threads.mutex.unlock();

Thread::idle_loop(); // Force a call to base class idle_loop()

// In the helpful master concept, a master can help only a sub-tree of its
// split point and because everything is finished here, it's not possible
// for the master to be 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();
}

// wait_for_think_finished() waits for main thread to go to sleep then returns
// ThreadPool::wait_for_think_finished() waits for main thread to finish the search

void ThreadPool::wait_for_think_finished() {

Expand All @@ -348,11 +354,11 @@ void ThreadPool::wait_for_think_finished() {
}


// 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, StateStackPtr& states) {
// ThreadPool::start_thinking() wakes up the main thread sleeping in
// MainThread::idle_loop() and starts a new search, then returns immediately.

void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
StateStackPtr& states) {
wait_for_think_finished();

SearchTime = Time::now(); // As early as possible
Expand Down

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