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Fix some races in SMP code

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When a search fails high then sp->alpha is increased and
slave threads are requested to stop.

So we have to check for a stop request before to start a search
otherwise we could end up with sp->alpha >= sp->beta
leading to an assert in debug run in search_pv().

This patch fixes the assert and get rid of some of possible races.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-01-24 13:46:27 +01:00
parent eb6ddd54f1
commit 3975a2b94f
1 changed files with 15 additions and 6 deletions
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21
src/search.cpp
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@ -2009,7 +2009,14 @@ namespace {
if (sp->ply == 1 && RootMoveNumber == 1)
Threads[threadID].failHighPly1 = true;
value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
// If another thread has failed high then sp->alpha has been increased
// to be higher or equal then beta, if so, avoid to start a PV search.
localAlpha = sp->alpha;
if (localAlpha < sp->beta)
value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID);
else
assert(thread_should_stop(threadID));
Threads[threadID].failHighPly1 = false;
}
}
@ -2027,11 +2034,7 @@ namespace {
sp->bestValue = value;
if (value > sp->alpha)
{
sp->alpha = value;
sp_update_pv(sp->parentSstack, ss, sp->ply);
if (value == value_mate_in(sp->ply + 1))
ss[sp->ply].mateKiller = move;
// Ask threads to stop before to modify sp->alpha
if (value >= sp->beta)
{
for (int i = 0; i < ActiveThreads; i++)
@ -2040,6 +2043,12 @@ namespace {
sp->finished = true;
}
sp->alpha = value;
sp_update_pv(sp->parentSstack, ss, sp->ply);
if (value == value_mate_in(sp->ply + 1))
ss[sp->ply].mateKiller = move;
}
// If we are at ply 1, and we are searching the first root move at
// ply 0, set the 'Problem' variable if the score has dropped a lot