pthread: implement rwlocks

[adamgreloch]

TASK: RTOS-1389

Description

Motivation and Context

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (list targets here).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[gemini-code-assist]

Code Review

This pull request implements POSIX read-write locks (pthread_rwlock_t and pthread_rwlockattr_t) and adds the pthread_testcancel cancellation point. The review feedback highlights several critical issues and improvement opportunities: standard POSIX functions should return positive error codes instead of negative ones, and local variable shadowing should be resolved in pthread_rwlock_lazy_init. Additionally, missing NULL checks in pthread_rwlockattr_setpshared, pthread_rwlock_destroy, and timespec_is_valid should be added to prevent potential crashes. The initialized field in pthread_rwlock_t should be declared as volatile int to ensure thread safety, and the return type of timespec_is_valid should be changed from time_t to int.

[github-actions]

[clang-format-pr] _{reported by reviewdog 🐶}
suggested fix

Suggested change

	#define PTHREAD_RWLOCK_INITIALIZER { 0 }
	#define PTHREAD_RWLOCK_INITIALIZER \
	{ \
	0 \
	}

[adamgreloch]

?

[adamgreloch]

/gemini review

[gemini-code-assist]

Code Review

This pull request implements POSIX read-write locks (pthread_rwlock_t and pthread_rwlockattr_t) and adds support for thread cancellation via pthread_testcancel. The review feedback highlights two critical issues: a potential segmentation fault in timespec_is_valid due to a missing NULL check on the time pointer, and a concurrency bug in the cancellation logic where cleanup handlers and key data lists can be executed or freed twice, leading to double-free or use-after-free vulnerabilities.

[github-actions]

Unit Test Results

11 307 tests   10 600 ✅  52m 55s ⏱️
   690 suites     707 💤
     1 files         0 ❌

Results for commit 3a3e9ee.