[3.x] Fix potential grain timer deadlock during disposal #8949
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ReubenBond
commented
Apr 20, 2024
| { | ||
| // This is called under a lock, so ensure that the method yields before invoking a callback | ||
| // which could take a different lock and potentially cause a deadlock. | ||
| await Task.Yield(); |
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This is the crux of the fix: under the lock, we forward the call to this method, which immediately yields, releasing the lock before the callback is invoked. This way, the callback will not be invoked under the lock and the potential for a deadlock is eliminated.
ReubenBond
commented
Apr 20, 2024
| } | ||
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| private void DisposeTimer() | ||
| { | ||
| var tmp = timer; | ||
| if (tmp == null) return; | ||
| var asyncTimer = Interlocked.CompareExchange(ref timer, null, timer); |
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Rather than taking a lock during disposal, we can use an interlocked operation. This allows us to atomically set the timer to null so that we can dispose it. Note that the existing code sets the timer to null outside of a lock anyway: the new version of the code uses timer is { IsStarted: true } instead of asyncCallback is null to check if the timer has been disposed.
This was referenced Apr 20, 2024
benjaminpetit
approved these changes
Apr 23, 2024
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Fixes #7865
To prevent the deadlock, we yield before invoking the timer callback. See comment.
Microsoft Reviewers: Open in CodeFlow