perf(rc): improve performance of subprocess service sharing

[brettlangdon]

This change will only write service names to the shared file queue only if we have not shared that service name yet.

This improvement avoids locking and writing to disk every time we call Pin.onto which can happen a lot when database connections are cycled/recreated frequently.

It also helps ensure that the same process doesn't continually write the same service name to the same file over and over again.

I also updated the tests to use subprocesses/forking as is expected with it's behavior for RC.

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/settings/_config.py                                             @DataDog/apm-core-python
tests/internal/service_name/test_extra_services_names.py                @DataDog/apm-core-python

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 282 ± 5 ms.

The average import time from base is: 286 ± 7 ms.

The import time difference between this PR and base is: -3.4 ± 0.3 ms.

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 2.075 ms (0.73%)

ddtrace.bootstrap.sitecustomize 1.390 ms (0.49%)

ddtrace.bootstrap.preload 1.390 ms (0.49%)

ddtrace.internal.remoteconfig.client 0.656 ms (0.23%)

ddtrace 0.685 ms (0.24%)

ddtrace.internal._unpatched 0.033 ms (0.01%)

json 0.033 ms (0.01%)

json.decoder 0.033 ms (0.01%)

re 0.033 ms (0.01%)

enum 0.033 ms (0.01%)

types 0.033 ms (0.01%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-06-16 19:21:19

Comparing candidate commit 4848444 in PR branch brettlangdon/perf.extra_services with baseline commit 5692392 in branch main.

Found 0 performance improvements and 4 performance regressions! Performance is the same for 474 metrics, 2 unstable metrics.

scenario:iastaspectsospath-ospathnormcase_aspect

• 🟥 execution_time [+344.743ns; +394.705ns] or [+9.928%; +11.367%]

scenario:iastaspectsospath-ospathsplit_aspect

• 🟥 execution_time [+624.233ns; +807.635ns] or [+12.941%; +16.743%]

scenario:iastaspectsospath-ospathsplitdrive_aspect

• 🟥 execution_time [+352.788ns; +403.078ns] or [+9.697%; +11.079%]

scenario:telemetryaddmetric-flush-1-metric

• 🟥 execution_time [+305.681ns; +456.522ns] or [+7.378%; +11.018%]

[brettlangdon]

I have to fix up the multiple_os_tests which use this test.