Description

SampleType field in ThreadSample event from Microsoft-DotNETCore-SampleProfiler is supposed to report if the thread was executing a managed code when the sample was taken. It should have the value EP_SAMPLE_PROFILER_SAMPLE_TYPE_MANAGED in this case and EP_SAMPLE_PROFILER_SAMPLE_TYPE_EXTERNAL otherwise.

It was working as expected until .NET 9, but doesn't work anymore.

Reproduction Steps

Actually, it's enough to take any application that performs active calculation in C#. We expect a majority of samples to have SampleType == EP_SAMPLE_PROFILER_SAMPLE_TYPE_MANAGED in this case.
As an example, https://github.com/JetBrains/DPA-demo can be taken.

Then run an EventPipe session with enabled sampling for the corresponding application, and look at ThreadSample event from Microsoft-DotNETCore-SampleProfiler.

Expected behavior

A majority of samples has SampleType == EP_SAMPLE_PROFILER_SAMPLE_TYPE_MANAGED.

Actual behavior

All (or almost all) samples have SampleType == EP_SAMPLE_PROFILER_SAMPLE_TYPE_EXTERNAL.

Regression?

Yes, it was working as expected in .NET 8 and earlier, but doesn't work in .NET 9 and .NET 10.

Known Workarounds

No workarounds

Configuration

I have checked the following .NET versions:

• 8.0.15 ✅
• 9.0.12 ❌
• 10.0.2 ❌

I reproduced it on macOS 15.7.3 (aarch64), but it definitely reproduces on Linux x64 too.
I don't think that the issue relates to a specific OS, it looks like some common problem in .NET runtime 9+.

Other information

No response