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author | Alexandre Ganea <alexandre.ganea@ubisoft.com> | 2021-09-18 12:00:17 -0400 |
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committer | Tom Stellard <tstellar@redhat.com> | 2021-12-16 11:02:34 -0800 |
commit | 87ca22cba2fad9bbf553a74eced3b7bb69e187be (patch) | |
tree | 8c391874652c89e9cb4f71ccdd1c23bf09b4fa0a | |
parent | d904698b53e4f21a675d4ca0463843432ff4d590 (diff) | |
download | llvm-87ca22cba2fad9bbf553a74eced3b7bb69e187be.tar.gz |
[Support] Attempt to fix deadlock in ThreadGroup
This is an attempt to fix the situation described by https://reviews.llvm.org/D104207#2826290 and PR41508.
See sequence of operations leading to the bug in https://reviews.llvm.org/D104207#3004689
We ensure that the Latch is completely "free" before decrementing the number of TaskGroupInstances.
Differential revision: https://reviews.llvm.org/D109914
(cherry picked from commit 7b25fa8c7a151e94be46ed8f0a56bf4e2af1c104)
-rw-r--r-- | llvm/include/llvm/Support/Parallel.h | 5 | ||||
-rw-r--r-- | llvm/lib/Support/Parallel.cpp | 7 |
2 files changed, 10 insertions, 2 deletions
diff --git a/llvm/include/llvm/Support/Parallel.h b/llvm/include/llvm/Support/Parallel.h index 28d171d45256..5c3b26d5754c 100644 --- a/llvm/include/llvm/Support/Parallel.h +++ b/llvm/include/llvm/Support/Parallel.h @@ -40,7 +40,10 @@ class Latch { public: explicit Latch(uint32_t Count = 0) : Count(Count) {} - ~Latch() { sync(); } + ~Latch() { + // Ensure at least that sync() was called. + assert(Count == 0); + } void inc() { std::lock_guard<std::mutex> lock(Mutex); diff --git a/llvm/lib/Support/Parallel.cpp b/llvm/lib/Support/Parallel.cpp index 9a2e1003da5a..71e3a1362f7e 100644 --- a/llvm/lib/Support/Parallel.cpp +++ b/llvm/lib/Support/Parallel.cpp @@ -151,7 +151,12 @@ static std::atomic<int> TaskGroupInstances; // lock, only allow the first TaskGroup to run tasks parallelly. In the scenario // of nested parallel_for_each(), only the outermost one runs parallelly. TaskGroup::TaskGroup() : Parallel(TaskGroupInstances++ == 0) {} -TaskGroup::~TaskGroup() { --TaskGroupInstances; } +TaskGroup::~TaskGroup() { + // We must ensure that all the workloads have finished before decrementing the + // instances count. + L.sync(); + --TaskGroupInstances; +} void TaskGroup::spawn(std::function<void()> F) { if (Parallel) { |