Fix potential torn reads by counters #1073
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gfoidl
reviewed
Oct 9, 2020
| @@ -136,31 +136,31 @@ protected override void OnEventCommand(EventCommandEventArgs command) | |||
| // This is the convention for initializing counters in the RuntimeEventSource (lazily on the first enable command). | |||
| // They aren't disabled afterwards... | |||
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| _totalCallsCounter ??= new PollingCounter("total-calls", this, () => _totalCalls) | |||
| _totalCallsCounter ??= new PollingCounter("total-calls", this, () => Volatile.Read(ref _totalCalls)) | |||
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It's about Interlocked.Read vs. Volatile.Read.
In ASP.NET Core for the kestrel counters I've used Volatile.Read, which does the correct read, then opened dotnet/docs#20984 to update the docs. The consensus over there is to use Interlocked.Read as it's documented to prevent torn-reads.
I'm fine with either variant here, just wanted to point this fact out (and for completeness).
JunTaoLuo
approved these changes
Oct 12, 2020
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32bit and ARM might have a torn read of counter
longvalues. Volatile ensures correct value is always read.