Fix AV in host from tracing on exit

[elinor-fung]

Fix #75760

For tracing, we had a static for the mutex which has a destructor. If a thread calls exit, the static destructor was called on that thread with no synchronization with other threads, resulting in potential issues where they would try to use the destructed object.

This change switches to using a spin lock. In the majority of cases (running an application, tracing not enabled, no errors) we won't use it at all. When we do (tracing explicitly enabled, errors, commands for printing info), we don't expect much contention, since most hosting is on a single thread.

Related:

• Host: Consider removing of destructors on types used for statics #36580

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Issue Details

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Fix #75760

For tracing, we had a static for the mutex which has a destructor. If a thread calls exit, the static destructor was called on that thread with no synchronization with other threads, resulting in potential issues where they would try to use the destructed object.

This change just stores the pointer instead. It does have the following effects:

• Mutex is only created when needed - in the majority of cases (running an application, tracing not enabled, no errors) it is not needed
• If it is created, it does not get deleted - it is left around until the process exists

Related:

• Host: Consider removing of destructors on types used for statics #36580

Author:	elinor-fung
Assignees:	-
Labels:	area-Host
Milestone:	-

[mgexo]

On a side, note, I really do not understand why you didnt check for g_trace_file != nullptr in trace::flush() before you even lock.
Thats what I also wrote in #75760 because in most (probably 99% of all environments), the trace feature is not even used and there is simply a useless lock at the end

[elinor-fung]

Avoiding the lock at the end when it is not needed is definitely reasonable - and an improvement I will look at. However, the underlying root cause for the issue is the static object with a destructor, so that is what I wish to fix here.

[elinor-fung]

/backport to release/6.0-staging

[github-actions]

Started backporting to release/6.0-staging: https://github.com/dotnet/runtime/actions/runs/8744005173