[runtime] Don't do GC Unsafe transition in mono_gchandle_free #15214
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…hed to the runtime. Some profiler events (for example gc_handle_deleted) could be raised on threads that aren't attached to the runtime. Since the thread won't participate in Mono's stop the world (since the runtime can't see it), there's no need to do the transition to GC Safe while the thread is trying to grab the profiler buffer lock.
Xamarin.Mac can call back here from a native thread that isn't attached to the runtime. SGen gchandle code is lockfree, and the profiler event can fire without involving Mono.
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Sample stack trace: |
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Please cherry pick to 2019-02 and notify us when it lands. |
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@monojenkins backport to 2019-06 |
This was referenced Jun 18, 2019
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Revert one part of #14979 -
mono_gchandle_freecan be called by Xamarin.Mac formxamarin_dispose_helperwhich can run on a thread that's not attached to the runtime.This is fine for SGen since the gchandle code is lockfree.
SGen also calls back into Mono, which fires a profiler event. The profiler has its own mechanism for tracking threads, but in
buffer_lock()we need to make sure that we don't do the Mono thread state transitions if the thread is attached to the profiler but not to Mono.Follow-up PR for #14975