refactor(profiling): add more GIL assertions to memalloc

[nsrip-dd]

The first GIL assertion I added, to memalloc_add_event, has not tripped
yet on a test application. One the one hand, it's reassuring that we
always see the GIL in that part of the code. On the other hand, there
are other parts of the memory profiler that could in theory be called
concurrently where I didn't add the assertion: when stopping the
profiler, and when iterating over the events to aggregate them. Add GIL
assertions to those points. The goal is ultimately to understand why we
needed to add locks to the profiler to prevent it from crashing, given
that the GIL exists.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
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• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/profiling/collector/_memalloc.c                                 @DataDog/profiling-python

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: nick.ripley/more-gil-assertions
Commit report: 1e58b3f
Test service: dd-trace-py

✅ 0 Failed, 130 Passed, 1468 Skipped, 4m 19.34s Total duration (35m 29.02s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-17 16:59:54

Comparing candidate commit 1e58b3f in PR branch nick.ripley/more-gil-assertions with baseline commit f67a358 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 394 metrics, 2 unstable metrics.

[taegyunkim]

memalloc module has 4 functions, start(), stop(), heap(), iter_events(). You've added the assert to stop() and iter_events() in this PR. Was there any specific reason to leave heap()?

[nsrip-dd]

memalloc module has 4 functions, start(), stop(), heap(), iter_events(). You've added the assert to stop() and iter_events() in this PR. Was there any specific reason to leave heap()?

Fair point. For now I'm focusing just on the allocation profiler stuff and not heap because we found that the crashes went away when adding locks to just the allocation profiler.