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Do not return from idle_loop() with lock held

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Master thread returns from idle_loop() when sp->cpus == 0,
but cpus is decremented by slave threads under sp->lock,
so it could happen that we return in split(), where we release
the split point, with sp->lock still held.

This patch guarantees that sp->lock is released when returning
to split().

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-05-02 12:02:41 +01:00
parent b89733b46c
commit f16c231bc9
1 changed files with 11 additions and 6 deletions
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17
src/search.cpp
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@ -82,7 +82,7 @@ namespace {
bool thread_should_stop(int threadID) const;
void wake_sleeping_threads();
void put_threads_to_sleep();
void idle_loop(int threadID, SplitPoint* waitSp);
void idle_loop(int threadID, SplitPoint* sp);
bool split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
@ -2636,10 +2636,10 @@ namespace {
// idle_loop() is where the threads are parked when they have no work to do.
// The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
// The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
// object for which the current thread is the master.
void ThreadsManager::idle_loop(int threadID, SplitPoint* waitSp) {
void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
assert(threadID >= 0 && threadID < MAX_THREADS);
@ -2649,7 +2649,7 @@ namespace {
// master should exit as last one.
if (AllThreadsShouldExit)
{
assert(!waitSp);
assert(!sp);
threads[threadID].state = THREAD_TERMINATED;
return;
}
@ -2658,7 +2658,7 @@ namespace {
// instead of wasting CPU time polling for work.
while (AllThreadsShouldSleep || threadID >= ActiveThreads)
{
assert(!waitSp);
assert(!sp);
assert(threadID != 0);
threads[threadID].state = THREAD_SLEEPING;
@ -2695,8 +2695,13 @@ namespace {
// If this thread is the master of a split point and all threads have
// finished their work at this split point, return from the idle loop.
if (waitSp != NULL && waitSp->cpus == 0)
if (sp && sp->cpus == 0)
{
// Because sp->cpus is decremented under lock protection,
// be sure sp->lock has been released before to proceed.
lock_grab(&(sp->lock));
lock_release(&(sp->lock));
assert(threads[threadID].state == THREAD_AVAILABLE);
threads[threadID].state = THREAD_SEARCHING;