[Breaking change]: 6.0 servicing change to EventSource callback behavior

[davmason]

Description

PR #84680 includes a breaking change in the June 6.0 servicing release

Version

Other (please put exact version in description textbox)

Previous behavior

Prior to this change, we would issue the EventSource.OnEventCommand callback for a EventCommand.Disable prior to setting m_eventSourceEnabled=false. This means that IsEnabled would return true in the OnEventCommand callback for a user EventSource, even if the command would lead to the EventSource being disabled.

The callback happens after we turn off the ability to dispatch events though, so even if an EventSource tries to fire an event it will not be written. Also, for EventCommand.Enable we issue a consistent view - IsEnabled accurately reports the state of the world, and the EventSource can write events from the OnEventCommand callback. This change makes the EventCommand.Disable behavior match the Enable behavior.

New behavior

The change makes the callbacks consistent, now we will mark the EventSource as disabled before the callback.

Type of breaking change

• Binary incompatible: Existing binaries may encounter a breaking change in behavior, such as failure to load or execute, and if so, require recompilation.
• Source incompatible: When recompiled using the new SDK or component or to target the new runtime, existing source code may require source changes to compile successfully.
• Behavioral change: Existing binaries may behave differently at run time.

Reason for change

This change was necessary to support multiple EventCounters instances, which has been requested as a blocker by multiple internal and external customers

Recommended action

I can't think of a scenario where the old behavior is desired, there is no way to revert to it.

Feature area

Core .NET libraries

Affected APIs

No response

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Associated WorkItem - 97022