From 9e479e4763df7801a7da3209f69dcb4875645552 Mon Sep 17 00:00:00 2001 From: Justin Lebar Date: Wed, 6 Apr 2016 23:46:40 +0000 Subject: [PATCH] Fix a race condition in support library ThreadPool. By running TSAN on the ThreadPool unit tests it was discovered that the threads in the pool can pop tasks off the queue at the same time the "wait" routine is trying to check if the task queue is empty. This patch fixes this problem by checking for active threads in the waiter before checking whether the queue is empty. Patch by Jason Henline. Differential Revision: http://reviews.llvm.org/D18811 Reviewers: joker.eph, jlebar llvm-svn: 265618 --- llvm/lib/Support/ThreadPool.cpp | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/llvm/lib/Support/ThreadPool.cpp b/llvm/lib/Support/ThreadPool.cpp index d4dcb2e..db03a4d 100644 --- a/llvm/lib/Support/ThreadPool.cpp +++ b/llvm/lib/Support/ThreadPool.cpp @@ -75,8 +75,11 @@ ThreadPool::ThreadPool(unsigned ThreadCount) void ThreadPool::wait() { // Wait for all threads to complete and the queue to be empty std::unique_lock LockGuard(CompletionLock); + // The order of the checks for ActiveThreads and Tasks.empty() matters because + // any active threads might be modifying the Tasks queue, and this would be a + // race. CompletionCondition.wait(LockGuard, - [&] { return Tasks.empty() && !ActiveThreads; }); + [&] { return !ActiveThreads && Tasks.empty(); }); } std::shared_future ThreadPool::asyncImpl(TaskTy Task) { -- 2.7.4