Environment variable DOTNET_DbgEnableMiniDump=1 doens't work when unhandled exception occurs in worker thread

[KurokiYukari]

Description

I run a .NET application with environment variable DOTNET_DbgEnableMiniDump=1. If an unhandled exception
occurs in main thread, the dump file is generated correctly. But if an unhandled exception occurs in worker thread, no dump file is generated.

Reproduction Steps

using powershell on windows:

1. dotnet new console
2. Change Program.cs to

var thread = new Thread(() =>
{
    throw new Exception();
});
thread.Start();
thread.Join();

3. run $env:DOTNET_DbgEnableMiniDump=1
4. run dotnet run

Expected behavior

Dump is generated and placed in %LocalAppData%/Temp dir.

Actual behavior

No dump is generated.
Console output:

Unhandled exception. System.Exception: Exception of type 'System.Exception' was thrown.
   at Program.<>c.<<Main>$>b__0_0() in C:\dumptest\Program.cs:line 3

Regression?

No response

Known Workarounds

No response

Configuration

1. Which version of .NET is the code running on? - 8.0.300
2. What OS and version, and what distro if applicable? - windows11 23H2
3. What is the architecture (x64, x86, ARM, ARM64)? - x64
4. Do you know whether it is specific to that configuration? -no. I have tried .NET 6, but also no dump file is generated.

Other information

No response

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[hoyosjs]

threadpool threads don't exhibit this behavior. this works:

await Task.Run(async () =>
{
    await Task.Yield();
    throw new Exception();
});

[KurokiYukari]

@hoyosjs I tried threadpool. it also doesn't work:

ThreadPool.QueueUserWorkItem(state =>
{
    throw new Exception();
});

Task works because unhandled exceptions that are thrown by user code that is running inside a task are propagated back to the calling thread(main thread)

[mikem8361]

It works in .NET 9. I did get it to repro on .NET 8. I'm not sure what change went into 9.0 that fixes this yet.

Hello, World!

Unhandled exception. System.Exception: Exception of type 'System.Exception' was thrown.
   at Program.<>c.<<Main>$>b__0_0() in C:\sd\builds\background\Program.cs:line 7
[createdump] Writing minidump with heap for process 14676 to file c:\sd\builds\background\createdump.9.0.0.dmp
[createdump] Dump successfully written in 922ms

[mikem8361]

It looks like this was fixed as part of the new exception handling support. Not sure what part or where, but on .NET 9 if I disable the new exception handling with set DOTNET_LegacyExceptionHandling=1 dumps are not generated anymore.

@janvorli any thoughts?

[janvorli]

I think that we need to call CreateCrashDumpIfEnabled by the end of the following function if we want to make it work with legacy EH:

runtime/src/coreclr/vm/excep.cpp

Line 4873 in b2b0db0

DefaultCatchHandler(PEXCEPTION_POINTERS pExceptionPointers,

I've tried it and it worked.

[mikem8361]

Thanks Jan. We need to decide if this fix should go into .NET 9 for the legacy EH and if it should go into .NET 8 servicing?

@tommcdon?

[tommcdon]

For correctness I think we should try to fix the legacy exception scenario for .NET 9, and consider this
for .NET 8 servicing if we have a customer request.