Fix Celery Worker Deadlock

What's Actually Happening

Celery workers freeze and stop processing tasks. Tasks remain in pending state indefinitely.

The Error You'll See

```bash # Tasks stuck: $ celery -A myapp inspect active

No tasks in active queue, but pending tasks not processed ```

Why This Happens

1. 1.Task blocking - Task waiting on lock or resource
2. 2.Pool exhausted - All workers busy
3. 3.Memory pressure - Worker OOM
4. 4.Database lock - Long DB transaction
5. 5.Circular task dependency - Tasks waiting on each other

Step 1: Check Worker Status

```bash # Check workers: celery -A myapp inspect active

# Check reserved: celery -A myapp inspect reserved

# Check stats: celery -A myapp inspect stats ```

Step 2: Restart Workers

```bash # Stop workers: pkill -f celery

# Start with concurrency: celery -A myapp worker --concurrency=4 --loglevel=info

# Or with pool: celery -A myapp worker --pool=prefork --concurrency=4 ```

Step 3: Fix Blocking Tasks

```python # BAD: Blocking task @celery_app.task def blocking_task(): time.sleep(3600) # Blocks for 1 hour

# GOOD: Use async or break up: @celery_app.task def non_blocking_task(): # Use smaller subtasks for chunk in chunks: process_chunk.delay(chunk) ```

Step 4: Set Time Limits

@celery_app.task(time_limit=300, soft_time_limit=240)
def my_task():
    # Task will timeout after 5 minutes
    pass

Celery Worker Checklist

Verify the Fix

celery -A myapp inspect active
# Output: Tasks processing normally

Related Issues

• [Fix Celery Task Retry Loop](/articles/fix-celery-task-retry-loop)
• [Fix Celery Beat Schedule Not Running](/articles/fix-celery-beat-schedule-not-running)