Fix a deadlock in EventSource and CounterGroup #40259
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noahfalk
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Aug 6, 2020
src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/CounterGroup.cs
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src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/CounterGroup.cs
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src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/CounterGroup.cs
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src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/CounterGroup.cs
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src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/CounterGroup.cs
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src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/CounterGroup.cs
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src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/CounterGroup.cs
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noahfalk
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Aug 14, 2020
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Fix #40190
A deadlock can occur when the callback encountered in counter.WritePayload() contains a path that contains a EventSource constructor. EventSource constructor tries to take EventSource.EventListenerLock which may already be held by another thread. Simultaneously, the thread that holds to the EventListenerLock can be blocked on s_CounterGroupLock if it calls enable on an EventSource with EventCounter enabled, resulting in a deadlock.
Essentially the only change in this PR is taking out the call to counter.WritePayload(); to out of the scope of s_counterGroupLock. The fields in CounterGroup (both static and non-static) are still read/written inside s_counterGroupLock.
Note: We may need to backport this fix to 3.1.