An alternative TLS implementation to fix a crash on musl/aarch64

[zhengyu123]

What does this PR do?:
This PR is intended to replace thread_local variables (except Otel ones) with an alternative implementation, which is based on pthread_get/setspecific() API.

Motivation:
We have encountered a quite few defects related to TLS - whose implementation is compiler specific. In some circumstances, the implementation is very restrictive that does not fit our usage pattern - it manifests in SCP-1238

Additional Notes:
To limit the scope, I only replaced 3 thread locals in livenessTracker which led to the crash reported in SCP-1238](https://datadoghq.atlassian.net/browse/SCP-1238)

Converting ProfiledThread to use newly introduced ThreadLocal will be done in separate PR.

How to test the change?:

• CI tests
• New test case.

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a security review (run the dd:platform-security-review
  skill, or file a request via the PSEC review form).
  bewaire also runs automatically on every PR.
• This PR doesn't touch any of that.
• JIRA: PROF-15114

Unsure? Have a question? Request a review!

[dd-octo-sts]

CI Test Results

Run:#28179381105 | Commit:c40b882 | Duration: 13m 21s (longest job)

❌ 5 of 32 test jobs failed

Status Overview

JDK	glibc-aarch64/debug	glibc-amd64/debug	musl-aarch64/debug	musl-amd64/debug
8	-	✅	-	-
8-ibm	-	✅	-	-
8-j9	✅	✅	-	-
8-librca	-	-	❌	✅
8-orcl	-	✅	-	-
11	-	✅	-	-
11-j9	✅	✅	-	-
11-librca	-	-	❌	✅
17	✅	✅	-	-
17-graal	✅	✅	-	-
17-j9	✅	✅	-	-
17-librca	-	-	❌	✅
21	✅	✅	-	-
21-graal	✅	✅	-	-
21-librca	-	-	❌	✅
25	✅	✅	-	-
25-graal	✅	✅	-	-
25-librca	-	-	❌	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Failed Tests

musl-aarch64/debug / 8-librca

Job:View logs

No detailed failure information available. Check the job logs.

musl-aarch64/debug / 11-librca

Job:View logs

No detailed failure information available. Check the job logs.

musl-aarch64/debug / 25-librca

Job:View logs

No detailed failure information available. Check the job logs.

musl-aarch64/debug / 17-librca

Job:View logs

No detailed failure information available. Check the job logs.

musl-aarch64/debug / 21-librca

Job:View logs

No detailed failure information available. Check the job logs.

Summary: Total: 32 | Passed: 27 | Failed: 5

---

Updated: 2026-06-25 15:15:24 UTC

[datadog-prod-us1-4]

✨ Fix all issues with BitsAI

⚠️ Warnings

🚦 21 Pipeline jobs failed

DataDog/java-profiler | reliability-chaos-aarch64: [profiler+tracer, tcmalloc, 25.0.3-tem]

CI Run | test-matrix / test-linux-musl-aarch64 (11-librca, debug)

CI Run | test-matrix / test-linux-musl-aarch64 (17-librca, debug)

View all 21 failed jobs.

Useful? React with 👍 / 👎

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 5e184c8 | Docs | Datadog PR Page | Give us feedback!}

[dd-octo-sts]

Reliability & Chaos Results

❌ 1 failure(s) detected Pipeline: https://gitlab.ddbuild.io/DataDog/java-profiler/-/pipelines/121073174

❌ chaos: profiler tcmalloc amd64 21 0 3 temXchaos

Chaos harness crashed (RC=124)

[Copilot]

Pull request overview

This PR introduces a pthread-key-based ThreadLocal helper as an alternative to C++ thread_local, and migrates LivenessTracker’s per-thread random/subsampling state to use it (motivated by musl/aarch64 TLS issues). It also adds C++ unit tests validating the new TLS wrapper behavior.

Changes:

• Added ddprof-lib/src/main/cpp/threadLocal.h implementing a ThreadLocal<T> wrapper on top of pthread_key_*.
• Updated LivenessTracker::track() to replace thread_local PRNG/distribution/skipped-state with ThreadLocal instances.
• Added threadLocal_ut.cpp gtest coverage for ThreadLocal set/get semantics, per-thread isolation, and per-thread cleanup.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 12 comments.

File	Description
ddprof-lib/src/main/cpp/threadLocal.h	New pthread-key TLS abstraction (generic + double specialization).
ddprof-lib/src/main/cpp/livenessTracker.cpp	Switches liveness subsampling TLS state from thread_local to the new ThreadLocal wrapper.
ddprof-lib/src/test/cpp/threadLocal_ut.cpp	Adds gtests validating correctness and cleanup behavior of the new TLS wrapper.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit:13c88912f3

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit:1de7f18db7

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[rkennke]

There's still the destructor checks that I would like to have added in production code path, plus two (minor) C style casts that should be C++ casts.

[rkennke]

Thanks for making the changes. I'm approving this now.
You might want to add the else { assert .. } parts in the destructors, and I also did a quick pass and found more places where C-style casts could be done with C++ casts. I leave that up to you.