[release/8.0-staging] EventPipe: Don't clean up thread list on shutdown

[github-actions]

Backport of #96936 to release/8.0-staging

/cc @davmason

Customer Impact

• Customer reported
• Found internally

This was reported by an internal customer, they ported their app to 8.0 and observed that there was regularly crashes on process exit. This was tracked down to a race between shutdown and threads firing events. If _ep_threads_lock is accessed after it is cleaned up it will cause an AV.

Regression

• Yes (from .NET 6)
• No

Testing

Customer has verified the fix

Risk

Low - we are not cleaning up some resources now, which should have no impact on the process and be relatively safe.

[jeffschwMSFT]

approved. please get a code review. we will take for consideration in 8.0.x

[hoyosjs]

Do we need to document anything as breaking for the mono embedding scenarios?

[davmason]

Do we need to document anything as breaking for the mono embedding scenarios?

@lateralusX can correct me here, but I don't believe so. The worst case scenario is we leak a single lock, and the way the code is written we may have leaked it anyways, since the free only happens if _ep_threads is empty.

[lateralusX]

Do we need to document anything as breaking for the mono embedding scenarios?

@lateralusX can correct me here, but I don't believe so. The worst case scenario is we leak a single lock, and the way the code is written we may have leaked it anyways, since the free only happens if _ep_threads is empty.

Its fine, no need to document, but I do think we should have different ways of uninitializing EventPipe at some point in the future, one that assumes process dies and that we have less control of threads (like we have now) and another that is a more strict uninitialize assuming all threads have been stopped/killed before when EventPipe gets uninitialized, in that scenario we could do proper cleanup of all resources allocated.

[carlossanlop]

Friendly reminder that Monday February 12th is the Code Complete deadline for the March Release. Please make sure to send the email to Tactics requesting approval.