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Move some stuff out of lock protection in split()

Browse source 
We shouldn't need lock protection to increment
splitPointsCnt and set curSplitPoint of masterThread.

Anyhow because this code is very tricky and prone to
races bound the change in a single patch.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2012-02-19 10:32:06 +01:00
parent 821e1c7233
commit 3441e0075d
2 changed files with 9 additions and 8 deletions
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3
src/search.cpp
View file

@ -1906,9 +1906,6 @@ void Thread::idle_loop(SplitPoint* sp_master) {
Threads[master].wake_up();
}
}
// 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(!is_searching);
}

14
src/thread.cpp
View file

@ -317,7 +317,7 @@ Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
return bestValue;
// Pick the next available split point from the split point stack
SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt];
SplitPoint* sp = &masterThread.splitPoints[masterThread.splitPointsCnt++];
sp->parent = masterThread.curSplitPoint;
sp->master = master;
@ -337,6 +337,7 @@ Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
assert(masterThread.is_searching);
masterThread.curSplitPoint = sp;
int slavesCnt = 0;
// Try to allocate available threads and ask them to start searching setting
@ -359,9 +360,6 @@ Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
break;
}
masterThread.curSplitPoint = sp;
masterThread.splitPointsCnt++;
lock_release(splitLock);
lock_release(sp->lock);
@ -371,10 +369,16 @@ Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
// the thread will return from the idle loop when all slaves have finished
// their work at this split point.
if (slavesCnt || Fake)
{
masterThread.idle_loop(sp);
// 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(!masterThread.is_searching);
}
// We have returned from the idle loop, which means that all threads are
// finished. Note that setting is_searching and decreasing activeSplitPoints is
// finished. Note that setting is_searching and decreasing splitPointsCnt is
// done under lock protection to avoid a race with Thread::is_available_to().
lock_grab(sp->lock); // To protect sp->nodes
lock_grab(splitLock);