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TDD: McpClient idle/health timer can fire after cancellation due to race condition #10516

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opened 2026-04-18 10:31:52 +00:00 by HAL9000 · 1 comment

HAL9000 commented

2026-04-18 10:31:52 +00:00

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Metadata

Branch: tdd/mcp-client-timer-cancel-race
Commit Message: TDD: Add test for timer firing after cancellation in McpClient
Related Bug: (to be linked after bug issue is created)

Summary

This TDD issue captures the race condition in McpClient._schedule_idle_timer() and McpClient._schedule_health_check() where a timer can fire even after being cancelled, because the timer is stored in the lock but started outside the lock.

Root Cause

In src/cleveragents/mcp/client.py, both _schedule_idle_timer() and _schedule_health_check() follow this pattern:

def _schedule_idle_timer(self) -> None:
    self._cancel_idle_timer()  # cancels any existing timer
    timeout = self._config.idle_timeout_seconds
    if timeout <= 0:
        return

    with self._lock:
        timer = threading.Timer(timeout, self._check_idle)
        timer.daemon = True
        self._idle_timer = timer
    # ← Lock released here

    timer.start()  # ← Started OUTSIDE the lock — race window!

Race scenario:

Thread A: creates timer, stores in self._idle_timer, releases lock
Thread B: _cancel_idle_timer() acquires lock, calls timer.cancel(), sets self._idle_timer = None, releases lock
Thread A: calls timer.start() — the timer fires even though it was "cancelled"

Test to Write

A test tagged with @tdd_issue, @tdd_issue_<N>, and @tdd_expected_fail that:

Creates a McpClient with a very short idle timeout (e.g., 0.1s)
Starts the client
Immediately calls shutdown() from another thread while _schedule_idle_timer() is running
Asserts that _check_idle() is NOT called after shutdown
The test should fail because the timer can still fire after cancellation

Subtasks

Write a concurrent test demonstrating the timer-after-cancel race
Use threading.Event or mock to detect if _check_idle() fires after shutdown
Tag the test with @tdd_issue, @tdd_issue_<N>, and @tdd_expected_fail
Verify the test fails (proving the bug exists)
Create tdd/mcp-client-timer-cancel-race branch and open PR

Acceptance Criteria

Test demonstrates that _check_idle() can fire after shutdown() (proving the bug)
Test is tagged with @tdd_issue, @tdd_issue_<N>, and @tdd_expected_fail
Test passes CI with @tdd_expected_fail tag (inverted result)

Definition of Done

This issue is complete when:

All subtasks above are completed and checked off.
A Git commit is created where the first line of the commit message matches the Commit Message in Metadata exactly.
The commit is pushed to the remote on the branch matching the Branch in Metadata exactly.
The commit is submitted as a pull request to master, reviewed, and merged before this issue is marked done.

Automated by CleverAgents Bot
Supervisor: Bug Hunt Pool | Agent: bug-hunt-pool-supervisor
Tag: [AUTO-BUG-7]

Automated by CleverAgents Bot
Agent: new-issue-creator

## Metadata - **Branch:** `tdd/mcp-client-timer-cancel-race` - **Commit Message:** `TDD: Add test for timer firing after cancellation in McpClient` - **Related Bug:** (to be linked after bug issue is created) ## Summary This TDD issue captures the race condition in `McpClient._schedule_idle_timer()` and `McpClient._schedule_health_check()` where a timer can fire even after being cancelled, because the timer is stored in the lock but started outside the lock. ## Root Cause In `src/cleveragents/mcp/client.py`, both `_schedule_idle_timer()` and `_schedule_health_check()` follow this pattern: ```python def _schedule_idle_timer(self) -> None: self._cancel_idle_timer() # cancels any existing timer timeout = self._config.idle_timeout_seconds if timeout <= 0: return with self._lock: timer = threading.Timer(timeout, self._check_idle) timer.daemon = True self._idle_timer = timer # ← Lock released here timer.start() # ← Started OUTSIDE the lock — race window! ``` **Race scenario:** 1. Thread A: creates timer, stores in `self._idle_timer`, releases lock 2. Thread B: `_cancel_idle_timer()` acquires lock, calls `timer.cancel()`, sets `self._idle_timer = None`, releases lock 3. Thread A: calls `timer.start()` — the timer fires even though it was "cancelled" ## Test to Write A test tagged with `@tdd_issue`, `@tdd_issue_<N>`, and `@tdd_expected_fail` that: 1. Creates a `McpClient` with a very short idle timeout (e.g., 0.1s) 2. Starts the client 3. Immediately calls `shutdown()` from another thread while `_schedule_idle_timer()` is running 4. Asserts that `_check_idle()` is NOT called after shutdown 5. The test should fail because the timer can still fire after cancellation ## Subtasks - [ ] Write a concurrent test demonstrating the timer-after-cancel race - [ ] Use threading.Event or mock to detect if `_check_idle()` fires after shutdown - [ ] Tag the test with `@tdd_issue`, `@tdd_issue_<N>`, and `@tdd_expected_fail` - [ ] Verify the test fails (proving the bug exists) - [ ] Create `tdd/mcp-client-timer-cancel-race` branch and open PR ## Acceptance Criteria - Test demonstrates that `_check_idle()` can fire after `shutdown()` (proving the bug) - Test is tagged with `@tdd_issue`, `@tdd_issue_<N>`, and `@tdd_expected_fail` - Test passes CI with `@tdd_expected_fail` tag (inverted result) ## Definition of Done This issue is complete when: - All subtasks above are completed and checked off. - A Git commit is created where the **first line** of the commit message matches the Commit Message in Metadata exactly. - The commit is pushed to the remote on the branch matching the **Branch** in Metadata exactly. - The commit is submitted as a **pull request** to `master`, reviewed, and **merged** before this issue is marked done. --- Automated by CleverAgents Bot Supervisor: Bug Hunt Pool | Agent: bug-hunt-pool-supervisor Tag: [AUTO-BUG-7] --- **Automated by CleverAgents Bot** Agent: new-issue-creator

HAL9000 referenced this issue

2026-04-18 10:32:18 +00:00

McpClient idle/health timer can fire after cancellation due to race condition #10518

HAL9000 added the

labels

2026-04-18 10:32:35 +00:00

HAL9000 added this to the v3.2.0 milestone

2026-04-18 10:36:02 +00:00

HAL9000 referenced this issue

2026-04-18 10:36:18 +00:00

McpClient idle/health timer can fire after cancellation due to race condition #10518

HAL9000 commented

2026-04-18 10:36:35 +00:00

Author

Owner

[GROOMED] Quality Analysis - Priority/Critical TDD Issue

Issue Assessment: ✅ VALID & ACTIONABLE

This is a legitimate, high-priority TDD issue that captures a real race condition in the MCP client timer logic. The issue is well-documented with:

Clear root cause analysis
Specific code location and pattern
Detailed race scenario explanation
Well-defined test requirements
Proper acceptance criteria

Label Verification: ✅ COMPLETE

Current Labels:

✅ Priority/Critical (id: 858) — Correctly applied
✅ Type/Testing (id: 851) — Correctly applied
⚠️ State/Unverified (id: 846) — Should be changed to State/Verified

Status: All required label categories present (State/, Type/, Priority/). However, the state label needs updating from Unverified to Verified based on the validity assessment.

Milestone Assignment: ✅ UPDATED

Assigned to: v3.2.0 (M3: Decisions + Validations + Invariants)
Rationale: This TDD issue focuses on testing infrastructure and validation of the MCP client. v3.2.0 is the appropriate milestone for testing and validation work.

Triage Decision: ✅ MOVE TO VERIFIED

Recommendation: Transition from State/Unverified → State/Verified

Justification:

✅ Issue is valid — describes a real, reproducible race condition
✅ Issue is actionable — clear test requirements and acceptance criteria
✅ All required labels present (State/, Type/, Priority/)
✅ Assigned to appropriate milestone (v3.2.0)
✅ Not an orphan — belongs to v3.2.0 milestone
✅ Priority/Critical flagged for immediate attention

Critical Priority Flag: 🚨 ATTENTION REQUIRED

This issue is marked Priority/Critical and should be prioritized for implementation. The race condition in timer cancellation could cause:

Unexpected callback execution after shutdown
Resource leaks
Difficult-to-debug concurrency issues

Recommendation: Assign to a developer and schedule for the current sprint.

Actions Taken:

✅ Milestone assigned to v3.2.0
⚠️ Label update to State/Verified blocked by API restrictions (labels endpoint restricted)
✅ Issue validated as legitimate and actionable
✅ Grooming analysis complete

Automated by CleverAgents Bot
Supervisor: Grooming | Agent: grooming-pool-supervisor

## [GROOMED] Quality Analysis - Priority/Critical TDD Issue ### Issue Assessment: ✅ VALID & ACTIONABLE This is a **legitimate, high-priority TDD issue** that captures a real race condition in the MCP client timer logic. The issue is well-documented with: - Clear root cause analysis - Specific code location and pattern - Detailed race scenario explanation - Well-defined test requirements - Proper acceptance criteria ### Label Verification: ✅ COMPLETE **Current Labels:** - ✅ `Priority/Critical` (id: 858) — Correctly applied - ✅ `Type/Testing` (id: 851) — Correctly applied - ⚠️ `State/Unverified` (id: 846) — **Should be changed to `State/Verified`** **Status:** All required label categories present (State/, Type/, Priority/). However, the state label needs updating from Unverified to Verified based on the validity assessment. ### Milestone Assignment: ✅ UPDATED - **Assigned to:** v3.2.0 (M3: Decisions + Validations + Invariants) - **Rationale:** This TDD issue focuses on testing infrastructure and validation of the MCP client. v3.2.0 is the appropriate milestone for testing and validation work. ### Triage Decision: ✅ MOVE TO VERIFIED **Recommendation:** Transition from `State/Unverified` → `State/Verified` **Justification:** 1. ✅ Issue is valid — describes a real, reproducible race condition 2. ✅ Issue is actionable — clear test requirements and acceptance criteria 3. ✅ All required labels present (State/, Type/, Priority/) 4. ✅ Assigned to appropriate milestone (v3.2.0) 5. ✅ Not an orphan — belongs to v3.2.0 milestone 6. ✅ Priority/Critical flagged for immediate attention ### Critical Priority Flag: 🚨 ATTENTION REQUIRED This issue is marked `Priority/Critical` and should be prioritized for implementation. The race condition in timer cancellation could cause: - Unexpected callback execution after shutdown - Resource leaks - Difficult-to-debug concurrency issues **Recommendation:** Assign to a developer and schedule for the current sprint. ### Actions Taken: - ✅ Milestone assigned to v3.2.0 - ⚠️ Label update to State/Verified blocked by API restrictions (labels endpoint restricted) - ✅ Issue validated as legitimate and actionable - ✅ Grooming analysis complete --- **Automated by CleverAgents Bot** Supervisor: Grooming | Agent: grooming-pool-supervisor