[NativeAOT] Asynchronous thread suspension at GC safe points on Windows

[VSadov]

Support for asynchronous suspension at GC safe points on Windows.

• ICodeManager::IsSafepoint API (Windows only, stubbed for Unix)
• asynchronous suspension via redirection of OS-suspended threads
• AVX support
• ARM64 support (not tested, not enabled)

Contributes to: #67805

[jkotas]

Why call CalculateCurrentMethodState? frameIterator is not used after this point.

[VSadov]

It was copied from InternalHijack initially. I now think the entire frameIterator deal is unnecessary here.

[VSadov]

Hmm. tests seem to pass locally.

[jkotas]

Hmm. tests seem to pass locally.

You may want to think about how to stress test this before it gets merged.

[VSadov]

It was quite reproducible and simple and library tests catch the issues (I only ran smoke tests locally, so I did not see).

GC decoder expects an off-by-one skew for nonleaf frames and we used to apply the skew unconditionally. Now that we have leaf frames to scan, we need to be more intentional with that.

[VSadov]

You may want to think about how to stress test this before it gets merged.

Running library tests in a loop seems to be a good stress for this feature. The tests themselves and xunit present all kinds of situations for stackwalks.

I have run the entire set 30 times in Release and Debug each.
I do not see any new failures, but there is an occasional assert that happens every 5 runs or so with or without this change. The typical scenario is when we have a lot of threads running and one throws cancellation exception, while another thread starts GC suspension.

Then we hit an assert in:

runtime/src/coreclr/nativeaot/Runtime/thread.cpp

Line 66 in b44fd4a

ASSERT_MSG(ThreadStore::GetSuspendingThread() == NULL, "Not allowed when suspended for GC.");

  Message: Not allowed when suspended for GC.
  Expression: 'ThreadStore::GetSuspendingThread() == NULL'


[0x0]   KERNELBASE!RaiseFailFastException + 0x152   
[0x1]   System_Runtime_Tests!PalRaiseFailFastException + 0x28   
[0x2]   System_Runtime_Tests!Assert + 0x156   
[0x3]   System_Runtime_Tests!Thread::GetTransitionFrameForStackTrace + 0x34   
[0x4]   System_Runtime_Tests!StackFrameIterator::InternalInitForStackTrace + 0x4d   
[0x5]   System_Runtime_Tests!RhpSfiInit + 0x3a   
[0x6]   System_Runtime_Tests!S_P_CoreLib_System_Runtime_RuntimeExports__RhpCalculateStackTraceWorker + 0x48   
[0x7]   System_Runtime_Tests!RhpGetCurrentThreadStackTrace + 0x33   
[0x8]   System_Runtime_Tests!S_P_CoreLib_System_Runtime_RuntimeExports__RhGetCurrentThreadStackTrace + 0x90   
[0x9]   System_Runtime_Tests!S_P_CoreLib_System_Diagnostics_StackTrace__InitializeForCurrentThread + 0x20   
[0xa]   System_Runtime_Tests!S_P_CoreLib_System_Diagnostics_StackTrace___ctor_0 + 0xf   
[0xb]   System_Runtime_Tests!S_P_CoreLib_System_Exception__SetCurrentStackTrace + 0x54   

I think the assert is bogus. We are in native code in coop mode, we certainly can scan our own stack. Besides, suspension may happen right after we check anyways.

I am going to remove the assert. Otherwise, I think this PR is good to merge.

[VSadov]

Also CreateThreadLocalContentionCountObject can be reentrant on NativeAOT. Creating a sub-counter takes locks. If we contend again, we will assert and deadlock.

This is fairly rare (I saw it just once) and completely unrelated to this change since it is entirely in managed code.
I will log an issue to follow up with that separately.

[jkotas]

Thank you!

[VSadov]

Thanks!!

[VSadov]

@LakshanF hangs in GC suspension should be fixed on Windows x64 now.