Summary

Fixes gh-152356.

On Windows, profiling.sampling run --blocking could hang indefinitely after the target process had already exited, leaving an empty binary profile that could not be replayed.

The non-blocking sampling path already terminates correctly when the target exits, but the Windows blocking implementation classified the same process-exit condition differently.

Root Cause

During blocking sampling, the profiler pauses the target through the Windows remote debugging layer.

If the target process has already exited, NtSuspendProcess() fails. The Windows implementation currently reports this as a RuntimeError.

The sampling loop treats RuntimeError as a recoverable sampling failure and continues retrying, so profiling never finishes and the binary profile writer is never finalized.

Other platforms already report terminated processes as ProcessLookupError, which the sampling loop correctly treats as a terminal condition.

Changes

This patch updates the Windows implementation of _Py_RemoteDebug_StopAllThreads().

When NtSuspendProcess() fails because the target process has already terminated, the remote debugging layer now raises ProcessLookupError instead of RuntimeError.

Existing RuntimeError behaviour is preserved for genuine NtSuspendProcess() failures while alive processes are unaffected.

No other profiling behaviour changes.

Tests

Added a Windows-only regression test that:

• runs profiling.sampling run --binary --mode=cpu --blocking against a short-lived Python script,
• verifies the command exits successfully,
• verifies a non-empty binary profile is produced,
• verifies the generated profile can be replayed successfully.

Validation

Validated with:

• PCbuild\build.bat -p x64 -d
• PCbuild\amd64\python_d.exe -m unittest -v test.test_profiling.test_sampling_profiler.test_blocking.TestBlockingModeCLI
• PCbuild\amd64\python_d.exe -m test test_profiling
• PCbuild\amd64\python_d.exe -m test test_importlib test_subprocess
• manual verification of profiling.sampling run --blocking and profiling.sampling replay
• git diff --check

After this change, Windows blocking sampling terminates correctly once the target process exits and produces a valid replayable binary profile.