ICorProfilerCallback.AssemblyUnloadStarted is never called

[kevingosse]

Description

When loading an assembly into an AssemblyLoadContext, the methods AssemblyLoadStarted/AssemblyLoadFinished on ICorProfilerCallback are called as expected. However, when unloading the ALC, AssemblyUnloadStarted is not called (as far as I can tell).

I made extra sure with a debugger that the module was properly unloaded, yet the event is not raised.

I scanned through the code and the event is supposed to be raised by Assembly::StartUnload but it doesn't seem to be called anywhere. Same thing for Module::StartUnload.

Reproduction Steps

• Write an application that properly unloads an ALC
• Attach a profiler

Expected behavior

ICorProfilerCallback::AssemblyUnloadStarted should be called.

Actual behavior

ICorProfilerCallback::AssemblyUnloadStarted aren't called.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

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Issue Details

---

Description

When loading an assembly into an AssemblyLoadContext, the methods AssemblyLoadStarted/AssemblyLoadFinished on ICorProfilerCallback are called as expected. However, when unloading the ALC, AssemblyUnloadStarted/AssemblyUnloadFinished are not called (as far as I can tell).

I made extra sure with a debugger that the module was properly unloaded, yet the event is not raised.

I scanned through the code and the event is supposed to be raised by Assembly::StartUnload but it doesn't seem to be called anywhere. Same thing for Module::StartUnload.

Reproduction Steps

• Write an application that properly unloads an ALC
• Attach a profiler

Expected behavior

ICorProfilerCallback::AssemblyUnloadStarted and ICorProfilerCallback::AssemblyUnloadFinished should be called.

Actual behavior

ICorProfilerCallback::AssemblyUnloadStarted and ICorProfilerCallback::AssemblyUnloadFinished aren't called.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

Author:	kevingosse
Assignees:	-
Labels:	area-Diagnostics-coreclr
Milestone:	-

[teo-tsirpanis]

c.c. @davmason

[kevingosse]

I'm guessing it should happen somewhere around there: https://github.com/dotnet/runtime/blob/main/src/coreclr/vm/loaderallocator.cpp#L524

The ETW event is raised and the debugger is notified, but no love for the profiler.

[tommcdon]

Adding @davmason @janvorli for thoughts

[kevingosse]

I edited the issue: I initially thought that both AssemblyUnloadStarted and AssemblyUnloadFinished were missing, but I wasn't testing properly. Only AssemblyUnloadStarted is missing.

[janvorli]

I have looked through our sources and I have found that we don't have any call to the Assembly::StartUnload that would raise the event. I've found that the call was removed in early 5.0 by #204, but at that time, it was already not being called. I'll look into reenabling it.