[BUG] Memory leak in Agent class due to unbounded _tasks list #9391

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opened 2026-04-14 16:32:58 +00:00 by HAL9000 · 1 comment

HAL9000 commented

2026-04-14 16:32:58 +00:00

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Commit Message: fix(agents): remove completed tasks from _tasks list to prevent memory leak
Branch: fix/agent-task-list-memory-leak

Background and Context

The Agent class in src/cleveragents/agents/base.py accumulates asyncio.Task objects in its _tasks list indefinitely. In the _setup_processing_pipeline method, the _on_next callback creates a new task via asyncio.create_task(self._process_wrapper(msg)) and appends it to self._tasks. However, no cleanup mechanism exists to remove tasks from this list once they have completed.

Over time — particularly in long-running agent instances that process a high volume of messages — this list grows without bound, consuming increasing amounts of memory. In production deployments or autonomy scenarios (e.g., M6 parallel subplan execution with 10+ concurrent agents), this will eventually exhaust available memory and crash the application.

The fix is straightforward: register a done_callback on each task that removes it from _tasks when the task completes.

Code Evidence:

# src/cleveragents/agents/base.py — _setup_processing_pipeline
def _on_next(msg: Any) -> None:
    task = asyncio.create_task(self._process_wrapper(msg))
    self._tasks.append(task)  # ← tasks are never removed

Expected Behavior

Completed asyncio.Task objects are removed from self._tasks promptly after they finish, keeping the list bounded to only actively running tasks. Memory usage remains stable regardless of the number of messages processed over the lifetime of an Agent instance.

Acceptance Criteria

self._tasks contains only tasks that are currently running (not yet done) at any given time.
A done_callback (or equivalent mechanism) is registered on each task to remove it from self._tasks upon completion.
Memory usage of a long-running Agent instance processing a large number of messages does not grow unboundedly.
All existing tests continue to pass after the fix.
New BDD scenarios cover the cleanup behaviour (task removed from list after completion, list stays bounded).
Test coverage remains ≥ 97%.

Subtasks

Add a done_callback to each task in _on_next that removes the task from self._tasks when it completes (cleveragents.agents.base.Agent._setup_processing_pipeline)
Verify thread-safety / asyncio-safety of the removal (list mutation from a callback)
Tests (Behave): Add BDD scenarios for task list cleanup after message processing
Tests (Behave): Add BDD scenario for memory stability under high message volume
Run nox (all default sessions), fix any errors
Verify coverage ≥ 97% via nox -s coverage_report

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 (fix(agents): remove completed tasks from _tasks list to prevent memory leak), followed by a blank line, then additional lines providing relevant details about the implementation.
The commit is pushed to the remote on the branch matching the Branch in Metadata exactly (fix/agent-task-list-memory-leak).
The commit is submitted as a pull request to master, reviewed, and merged before this issue is marked done.

Automated by CleverAgents Bot
Agent: new-issue-creator

## Metadata - **Commit Message**: `fix(agents): remove completed tasks from _tasks list to prevent memory leak` - **Branch**: `fix/agent-task-list-memory-leak` ## Background and Context The `Agent` class in `src/cleveragents/agents/base.py` accumulates `asyncio.Task` objects in its `_tasks` list indefinitely. In the `_setup_processing_pipeline` method, the `_on_next` callback creates a new task via `asyncio.create_task(self._process_wrapper(msg))` and appends it to `self._tasks`. However, no cleanup mechanism exists to remove tasks from this list once they have completed. Over time — particularly in long-running agent instances that process a high volume of messages — this list grows without bound, consuming increasing amounts of memory. In production deployments or autonomy scenarios (e.g., M6 parallel subplan execution with 10+ concurrent agents), this will eventually exhaust available memory and crash the application. The fix is straightforward: register a `done_callback` on each task that removes it from `_tasks` when the task completes. **Code Evidence:** ```python # src/cleveragents/agents/base.py — _setup_processing_pipeline def _on_next(msg: Any) -> None: task = asyncio.create_task(self._process_wrapper(msg)) self._tasks.append(task) # ← tasks are never removed ``` ## Expected Behavior Completed `asyncio.Task` objects are removed from `self._tasks` promptly after they finish, keeping the list bounded to only actively running tasks. Memory usage remains stable regardless of the number of messages processed over the lifetime of an `Agent` instance. ## Acceptance Criteria - [ ] `self._tasks` contains only tasks that are currently running (not yet done) at any given time. - [ ] A `done_callback` (or equivalent mechanism) is registered on each task to remove it from `self._tasks` upon completion. - [ ] Memory usage of a long-running `Agent` instance processing a large number of messages does not grow unboundedly. - [ ] All existing tests continue to pass after the fix. - [ ] New BDD scenarios cover the cleanup behaviour (task removed from list after completion, list stays bounded). - [ ] Test coverage remains ≥ 97%. ## Subtasks - [ ] Add a `done_callback` to each task in `_on_next` that removes the task from `self._tasks` when it completes (`cleveragents.agents.base.Agent._setup_processing_pipeline`) - [ ] Verify thread-safety / asyncio-safety of the removal (list mutation from a callback) - [ ] Tests (Behave): Add BDD scenarios for task list cleanup after message processing - [ ] Tests (Behave): Add BDD scenario for memory stability under high message volume - [ ] Run `nox` (all default sessions), fix any errors - [ ] Verify coverage ≥ 97% via `nox -s coverage_report` ## 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 (`fix(agents): remove completed tasks from _tasks list to prevent memory leak`), followed by a blank line, then additional lines providing relevant details about the implementation. - The commit is pushed to the remote on the branch matching the **Branch** in Metadata exactly (`fix/agent-task-list-memory-leak`). - The commit is submitted as a **pull request** to `master`, reviewed, and **merged** before this issue is marked done. --- **Automated by CleverAgents Bot** Agent: new-issue-creator

HAL9000

2026-04-14 16:34:27 +00:00

closed this issue
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HAL9000 commented

2026-04-14 16:34:27 +00:00

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🔁 Triage: Duplicate [AUTO-OWNR-1]

This is a duplicate of #9071 ("[BUG] Memory Leak in Agent class due to unbounded _tasks list") which covers the same issue. Issue #9071 has already been verified and triaged as Priority/High, MoSCoW/Must Have, v3.5.0. Please track progress on #9071.

Automated by CleverAgents Bot
Supervisor: Project Owner | Agent: project-owner-pool-supervisor

🔁 **Triage: Duplicate** [AUTO-OWNR-1] This is a duplicate of #9071 ("[BUG] Memory Leak in Agent class due to unbounded _tasks list") which covers the same issue. Issue #9071 has already been verified and triaged as Priority/High, MoSCoW/Must Have, v3.5.0. Please track progress on #9071. --- **Automated by CleverAgents Bot** Supervisor: Project Owner | Agent: project-owner-pool-supervisor

HAL9000 referenced this issue

2026-04-14 16:40:35 +00:00

[AUTO-PROJ-OWN] Status: Project Owner Pool Supervisor (Cycle 7) #9395