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Fix a (theoretical) race leading to a crash

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After we release the SplitPoint lock the master, suppose
is main thread, can safely return and if a "quit" command
is pending, main thread exits and associated Thread object
is freed. So when we access master->is_searching a crash
occurs.

I have never found such a race that is of course very rare
becuase assumes that from lock releasing we go to sleep for
a time long enough for the main thread to end the search and
return. But you can never know, and anyhow a race is a race.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2012-04-06 15:22:02 +01:00
parent 5a2d525048
commit bed4075580
1 changed files with 9 additions and 9 deletions
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18
src/search.cpp
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@ -1826,7 +1826,6 @@ void Thread::idle_loop(SplitPoint* sp_master) {
Stack ss[MAX_PLY_PLUS_2];
Position pos(*sp->pos);
Thread* master = sp->master;
memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
(ss+1)->sp = sp;
@ -1848,17 +1847,18 @@ void Thread::idle_loop(SplitPoint* sp_master) {
sp->slavesMask &= ~(1ULL << idx);
sp->nodes += pos.nodes_searched();
// After releasing the lock we cannot access anymore any SplitPoint
// related data in a reliably way becuase it could have been released
// under our feet by the sp master.
lock_release(sp->lock);
// Wake up master thread so to allow it to return from the idle loop in
// case we are the last slave of the split point.
if ( Threads.use_sleeping_threads()
&& this != master
&& !master->is_searching)
master->wake_up();
&& this != sp->master
&& !sp->master->is_searching)
sp->master->wake_up();
// After releasing the lock we cannot access anymore any SplitPoint
// related data in a safe way becuase it could have been released under
// our feet by the sp master. Also accessing other Thread objects is
// unsafe because if we are exiting there is a chance are already freed.
lock_release(sp->lock);
}
}
}