[Python] How to get the number of background tasks currently running in a FastAPI application?

The below run_tasks FastAPI route handler spawns a background task on each HTTP call to the /run-tasks endpoint.

import asyncio
import time

from fastapi import APIRouter
from starlette.background import BackgroundTasks


router = APIRouter()


async def background_task(sleep_time: int, task_id: int):
print(f"Task {task_id} started")
await asyncio.sleep(sleep_time) # Simulate a long-running task
print(f"Task {task_id} completed")


@router.post("/run-tasks")
async def run_tasks(background_tasks: BackgroundTasks, sleep_time: int):
background_tasks.add_task(background_task, sleep_time, int(time.time()))
print(len(background_tasks.tasks))
return {"message": "NEW SLEEP query arg background task started"}


When a SIGTERM signal is sent to the process running this FastAPI app, the following sequence is observed in the logs:

1. Waiting for background tasks to complete appears.
2. Afterward, messages like "Task {some_id} completed" are logged.
3. Finally, the log shows "Waiting for application shutdown", and the application then shuts down.

Is there a way to get how many background tasks are currently running? I'd like to print the number of remaining tasks after each task completion (i.e., after print(f"Task {task_id} completed")).

My goal is to see '0' at the end, so that to be sure that all background tasks finished, before application shutdown.

I understand that a FastAPI app running in Python should wait for all background tasks to finish. However, I want to ensure this also happens when the app runs inside a container within a Kubernetes pod. This is crucial for correctly tuning the terminationGracePeriodSeconds parameter of the pod (see the relevant Termination of Pods documentation).

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