Fix/thread safety and logging

[Waqar53]

Summary

Three targeted fixes improving thread-safety and debuggability in core utilities. 24 new tests, 0 failures, all ruff checks pass.

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1. RPM Controller Thread-Safety & Timer Lifecycle Bugs

Files: utilities/rpm_controller.py, tests/utilities/test_rpm_controller.py (new)

Bug	Fix
_wait_for_next_minute() slept 60s holding the lock, blocking all threads	Wait outside lock using Event.wait(60)
_shutdown_flag read/written without lock (race condition)	Replaced with threading.Event (atomic)
Timer could fire after stop_rpm_counter()	Cancel under lock, check _shutdown_event
_lock could be None despite being required	Always initialized via default_factory

Tests added: 9 new dedicated tests (previously 0 existed for RPMController)

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2. RWLock Writer Starvation Fix

Files: utilities/rw_lock.py, tests/utilities/events/test_rw_lock.py

New readers could indefinitely starve waiting writers because r_acquire only checked if a writer held the lock, not if one was waiting.

Fix: Added _waiting_writers counter — standard practice for production RWLock implementations. r_acquire now blocks when _waiting_writers > 0. No behavior change when there are no waiting writers, so all 10 existing tests pass unchanged.

Tests added: 1 new test (test_writer_not_starved_by_continuous_readers)

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3. Debug Logging for OutputParser Retries (Closes #4246)

Files: utilities/agent_utils.py, tests/utilities/test_output_parser_logging.py (new)

Added logger.debug() to handle_output_parser_exception so every retry is logged at DEBUG level, regardless of verbose setting or iteration count.

Previously, retry information was only visible when verbose=True AND iterations exceeded log_error_after (default 3), making it nearly impossible to debug retry loops in production.

Tests added: 4 new tests

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Verification

# RPM Controller (9 tests)
pytest lib/crewai/tests/utilities/test_rpm_controller.py -v

# RWLock (11 tests — 10 existing + 1 new)
pytest lib/crewai/tests/utilities/events/test_rw_lock.py -v

# OutputParser logging (4 tests)
pytest lib/crewai/tests/utilities/test_output_parser_logging.py -v

# Linting
ruff check lib/crewai/src/crewai/utilities/rpm_controller.py lib/crewai/src/crewai/utilities/rw_lock.py lib/crewai/src/crewai/utilities/agent_utils.py

<!-- CURSOR_SUMMARY -->
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> [!NOTE]
> **Medium Risk**
> Touches core concurrency and rate-limiting utilities used across agents/crew; changes are well-covered by new multithreaded regression tests but could still affect timing-sensitive behavior in production.
> 
> **Overview**
> Adds **DEBUG-level logging** to `handle_output_parser_exception` so every `OutputParserError` retry records the iteration and error message independent of `verbose` settings.
> 
> Refactors `RPMController` to be thread-safe and stoppable: always initializes `_lock`, replaces the shutdown flag with a `threading.Event`, moves the rate-limit wait outside the lock, and ensures timer reset/stop operations are synchronized to avoid races and limit bypass on concurrent wakeups.
> 
> Updates `RWLock` to prevent writer starvation by blocking new readers when writers are queued, and adds regression tests for the new logging behavior, RPM controller lifecycle/limit correctness under concurrency, and RWLock fairness.
> 
> <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 8ace304570a039f7e8c2322319707b546db22463. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}

[cursor]

Nested read locks deadlock when writer is waiting

Medium Severity

The new _waiting_writers > 0 check in r_acquire introduces a deadlock for reentrant (nested) read locks under writer contention. If Thread A holds a read lock and Thread B calls w_acquire (incrementing _waiting_writers), Thread A's inner r_acquire blocks on _waiting_writers > 0, while Thread B blocks on _readers > 0 — neither can proceed. The existing test_nested_read_locks_same_thread test validates nested reads as a supported pattern but only passes because no writer is contending; under real-world contention it would deadlock.

Additional Locations (1)

• lib/crewai/tests/utilities/events/test_rw_lock.py#L242-L251