Background Tasks

Starlette contains an BackgroundTask class for in-process background tasks.

A background task should be attached to the response and run only once after the response has been sent.

background task

Use to add a single background task to the response.

Signed by: BackgroundTask(func, *args, **kwargs)

from starlette.applications import Starlette
from starlette.responses import JSONResponse
from starlette.routing import Route
from starlette.background import BackgroundTask


...

async def signup(request):
    data = await request.json()
    username = data['username']
    email = data['email']
    task = BackgroundTask(send_welcome_email, to_address=email)
    message = {'status': 'Signup successful'}
    return JSONResponse(message, background=task)

async def send_welcome_email(to_address):
    ...


routes = [
    ...
    Route('/user/signup', endpoint=signup, methods=['POST'])
]

app = Starlette(routes=routes)

background task

Use to add multiple background tasks to the response.

Signed by: BackgroundTasks(tasks=[])

from starlette.applications import Starlette
from starlette.responses import JSONResponse
from starlette.background import BackgroundTasks

async def signup(request):
    data = await request.json()
    username = data['username']
    email = data['email']
    tasks = BackgroundTasks()
    tasks.add_task(send_welcome_email, to_address=email)
    tasks.add_task(send_admin_notification, username=username)
    message = {'status': 'Signup successful'}
    return JSONResponse(message, background=tasks)

async def send_welcome_email(to_address):
    ...

async def send_admin_notification(username):
    ...

routes = [
    Route('/user/signup', endpoint=signup, methods=['POST'])
]

app = Starlette(routes=routes)

!!! Important tasks are executed sequentially. If one of the tasks throws an exception, subsequent tasks have no chance to execute.