fix(profiler): update memalloc guard

[sanchda]

Previously, the memory allocation profiler would use Python's builtin thread-local storage interfaces in order to set and get the state of a thread-local guard.

I've updated a few things here.

• I think get/set idioms are slightly problematic for this type of code, since it pushes the responsibility of maintaining clean internal state up to the parent. A consequence of this is that the propagation of the underlying state by value opens the door for race conditions if execution changes between contexts (unlikely here, but I think minimizing indirection is still cleaner). Accordingly, I've updated this to use native thread-local storage
• Based on @nsrip-dd's observation, I widened the guard over free() operations. I believe this is correct, and if it isn't then the detriment is performance, not correctness.
• I got rid of the PY37 failovers

We don't have any reproductions for the defects that prompted this change, but I've been running a patched library in an environment that does reproduce the behavior, and I haven't seen any defects.

1. I don't believe this patch is harmful, and if our memory allocation tests pass then I believe it should be fine.
2. I have a reason to believe this fixes a critical defect, which can cause crashes.

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
• Release note makes sense to a user of the library
• 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_reentrant.c                       @DataDog/profiling-python
releasenotes/notes/fix-profiling-memalloc-segfault-5593ad951405a75d.yaml  @DataDog/apm-python
ddtrace/internal/datadog/profiling/dd_wrapper/src/sample.cpp            @DataDog/profiling-python
ddtrace/profiling/collector/_memalloc.c                                 @DataDog/profiling-python
ddtrace/profiling/collector/_memalloc_heap.c                            @DataDog/profiling-python
ddtrace/profiling/collector/_memalloc_reentrant.h                       @DataDog/profiling-python
ddtrace/profiling/collector/_memalloc_tb.c                              @DataDog/profiling-python
ddtrace/profiling/collector/_pymacro.h                                  @DataDog/profiling-python
setup.py                                                                @DataDog/python-guild

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-12-19 19:06:17

Comparing candidate commit 655854b in PR branch sanchda/memalloc_lock with baseline commit 89d82c3 in branch main.

Found 0 performance improvements and 2 performance regressions! Performance is the same for 392 metrics, 2 unstable metrics.

scenario:flasksimple-profiler

• 🟥 execution_time [+1.483ms; +1.493ms] or [+74.345%; +74.830%]

scenario:iast_aspects-ospathsplit_aspect

• 🟥 execution_time [+410.779ns; +470.838ns] or [+10.678%; +12.239%]

[sanchda]

@nsrip-dd , could you I ask you to re-review? Your critical eye was very helpful in the last round and I'd like to enjoy its benefit for the final cut.