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Lifespan

Mangum supports the ASGI Lifespan protocol. This allows applications to define lifespan startup and shutdown event handlers.

from mangum import Mangum
from fastapi import FastAPI

app = FastAPI()


@app.on_event("startup")
async def startup_event():
    pass


@app.on_event("shutdown")
async def shutdown_event():
    pass


@app.get("/")
def read_root():
    return {"Hello": "World"}

handler = Mangum(app, lifespan="auto")

Configuring Lifespan events

Lifespan support is automatically determined unless explicitly turned on or off. A string value option is used to configure lifespan support, the choices are auto, on, and off.

Options

  • auto

    Application support for lifespan is inferred using the state transitions. Any error that occurs during startup will be logged and the ASGI application cycle will continue unless a lifespan.startup.failed event is sent.

  • on

    Application support for lifespan is explicit. Any error that occurs during startup will be raised and a 500 response will be returned.

  • off

    Application support for lifespan is ignored. The application will not enter the lifespan cycle context.

Defaults to auto.

State machine

The LifespanCycle is a state machine that handles ASGI lifespan events intended to run before and after HTTP and WebSocket requests are handled.

LifespanCycle

::: mangum.protocols.lifespan.LifespanCycle :docstring: :members: run receive send startup shutdown

Context manager

Unlike the HTTPCycle and WebSocketCycle classes, the LifespanCycle is also used as a context manager in the adapter class. If lifespan support is turned off, then the application never enters the lifespan cycle context.

 with ExitStack() as stack:
    # Ignore lifespan events entirely if the `lifespan` setting is `off`.
    if self.lifespan in ("auto", "on"):
        asgi_cycle: typing.ContextManager = LifespanCycle(
            self.app, self.lifespan
        )
        stack.enter_context(asgi_cycle)

The magic methods __enter__ and __exit__ handle running the async tasks that perform startup and shutdown functions.

    def __enter__(self) -> None:
        """
        Runs the event loop for application startup.
        """
        self.loop.create_task(self.run())
        self.loop.run_until_complete(self.startup())

    def __exit__(
        self,
        exc_type: typing.Optional[typing.Type[BaseException]],
        exc_value: typing.Optional[BaseException],
        traceback: typing.Optional[types.TracebackType],
    ) -> None:
        """
        Runs the event loop for application shutdown.
        """
        self.loop.run_until_complete(self.shutdown())

LifespanCycleState

::: mangum.protocols.lifespan.LifespanCycleState :docstring:
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