itest: use notification profiler API instead of main profiler slot

[korniltsev-grafanista]

What

Switch the integration test setup from registering Pyroscope as the main CLR profiler to registering it as a notification profiler.

Changed files:

• itest.Dockerfile — Docker-based integration test environment
• IntegrationTest/Makefile — local make run target

Before

CORECLR_ENABLE_PROFILING=1
CORECLR_PROFILER={BD1A650D-AC5D-4896-B64F-D6FA25D6B26A}
CORECLR_PROFILER_PATH=/path/to/Pyroscope.Profiler.Native.so

After

CORECLR_ENABLE_NOTIFICATION_PROFILERS=1
CORECLR_NOTIFICATION_PROFILERS=/path/to/Pyroscope.Profiler.Native.so={BD1A650D-AC5D-4896-B64F-D6FA25D6B26A}

Why

The .NET runtime only allows a single main profiler (CORECLR_PROFILER). Using the notification profiler API (CORECLR_NOTIFICATION_PROFILERS) allows Pyroscope to coexist with other profilers or tracers that already occupy the main profiler slot (e.g. OpenTelemetry, Datadog tracer). This makes the integration tests reflect real-world deployment scenarios more accurately.

LD_PRELOAD for Pyroscope.Linux.ApiWrapper.x64.so is unchanged — it is still required for the CPU/wall-time sampling to work correctly on Linux.

[chatgpt-codex-connector]

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[korniltsev-grafanista]

@codex review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Return notification mode only when explicitly needed

This now marks every profiler load as notification-only, not just the new integration-test path. Existing deployment scripts still load the profiler as the main profiler via CORECLR_PROFILER (profiler/src/ProfilerEngine/DeployResources/DDProf-SetEnv.sh:15-17), and those runs can request capabilities like COR_PRF_ENABLE_REJIT when managed code cache is enabled (CorProfilerCallback.cpp:1517-1520); however COR_PRF_ENABLE_REJIT is not included in COR_PRF_ALLOWABLE_NOTIFICATION_PROFILER (shared/src/native-lib/coreclr/src/inc/corprof.idl:597-617). Forcing notification mode here can therefore make event-mask setup fail and stop profiling in non-itest configurations.

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[aleks-p]

@korniltsev-grafanista

I tested this with OTEL auto-instrumentation running as the primary profiler and Pyroscope through the notification system. It worked, here it the testing code if you wanted to add it:

https://github.com/grafana/pyroscope-dotnet/compare/vk/39cb-in-the-integrati...test/otel-coexistence?expand=1

[korniltsev-grafanista]

Thanks <3 more tests

I opened a draft from your branch just incase so that we do not forget #236

I recently prompted this integration test change #235

I willlikely merge #236 after #235 but before #232

[korniltsev-grafanista-yolo-vibecoder239]

I've reviewed the changes in the context of the CoreCLR runtime source code.

The implementation of ICorProfilerCallback11 and LoadAsNotificationOnly looks correct for enabling the "Notification-Only" mode. This allows the profiler to be loaded alongside a main profiler (like a tracing APM) by signaling pbNotificationOnly = TRUE.

However, there is a potential blocking issue on ARM64.

1. ARM64 Incompatibility

On ARM64, the profiler forces UseManagedCodeCache to true in Configuration.cpp:

// Configuration.cpp
    bool defaultUseManagedCodeCache =
    #if ARM64
        true;
    #else
        false;
    #endif

When UseManagedCodeCache is enabled, CorProfilerCallback::Initialize adds COR_PRF_ENABLE_REJIT to the event mask:

// CorProfilerCallback.cpp
    if (_pConfiguration->UseManagedCodeCache())
    {
        eventMask |= COR_PRF_MONITOR_JIT_COMPILATION | COR_PRF_ENABLE_REJIT;
    }

The Problem:
In the CoreCLR runtime, COR_PRF_ENABLE_REJIT is not included in the allowable flags for a notification-only profiler (COR_PRF_ALLOWABLE_NOTIFICATION_PROFILER).

When SetEventMask is called by a notification-only profiler with COR_PRF_ENABLE_REJIT, the runtime will return E_INVALIDARG, and initialization will likely fail.

2. x64/x86 Safety

On x64/x86, UseManagedCodeCache defaults to false. The flags used (COR_PRF_MONITOR_THREADS, COR_PRF_ENABLE_STACK_SNAPSHOT, etc.) are all within the allowed set for notification profilers.
The profiler also correctly avoids calling restricted methods like SetILFunctionBody or SetEnterLeaveFunctionHooks.

Recommendation

You should verify the behavior on ARM64. If ManagedCodeCache (and thus COR_PRF_ENABLE_REJIT) is strictly required for ARM64 as the code suggests, this profiler cannot run as a notification-only profiler on that architecture.

You might need to add logic to LoadAsNotificationOnly to return FALSE on ARM64, or adjust the feature flags if possible.

[korniltsev-grafanista]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

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