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Fix four data races.

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the nodes, tbHits, rootDepth and lastInfoTime variables are read by multiple threads, but not declared atomic, leading to data races as found by -fsanitize=thread. This patch fixes this issue. It is based on top of the CI-threading branch (PR #1129), and should fix the corresponding CI error messages.

The patch passed an STC check for no regression:

http://tests.stockfishchess.org/tests/view/5925d5590ebc59035df34b9f
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 169597 W: 29938 L: 30066 D: 109593

Whereas rootDepth and lastInfoTime are not performance critical, nodes and tbHits are. Indeed, an earlier version using relaxed atomic updates on the latter two variables failed STC testing (http://tests.stockfishchess.org/tests/view/592001700ebc59035df34924), which can be shown to be due to x86-32 (http://tests.stockfishchess.org/tests/view/592330ac0ebc59035df34a89). Indeed, the latter have no instruction to atomically update a 64bit variable. The proposed solution thus uses a variable in Position that is accessed only by one thread, which is copied every few thousand nodes to the shared variable in Thread.

No functional change.

Closes #1130
Closes #1129
This commit is contained in:
Joost VandeVondele
2017-06-21 13:36:53 -07:00
committed by Joona Kiiski
parent 2c237da546
commit 3cb0200459
7 changed files with 78 additions and 17 deletions
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3
src/thread.cpp
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@@ -163,7 +163,7 @@ uint64_t ThreadPool::nodes_searched() const {
uint64_t nodes = 0;
for (Thread* th : *this)
nodes += th->rootPos.nodes_searched();
nodes += th->nodes;
return nodes;
}
@@ -212,6 +212,7 @@ void ThreadPool::start_thinking(Position& pos, StateListPtr& states,
{
th->maxPly = 0;
th->tbHits = 0;
th->nodes = 0;
th->rootDepth = DEPTH_ZERO;
th->rootMoves = rootMoves;
th->rootPos.set(pos.fen(), pos.is_chess960(), &setupStates->back(), th);