labthings_fastapi.dependencies.blocking_portal

FastAPI dependency for a blocking portal.

This allows dependencies that are called by threaded code to send things back to the async event loop. See Concurrency in LabThings-FastAPI for more details.

Threaded code can call asynchronous code in the anyio event loop used by fastapi, if an anyio.BlockingPortal is used.

The ThingServer sets up an anyio.from_thread.BlockingPortal when the server starts (in ThingServer.lifespan). This may be accessed from an action using the BlockingPortal dependency in this module.

Note

The blocking portal is accessed via a dependency to ensure we only ever use the blocking portal attached to the server handling the current request.

This may be simplified in the future, as a Thing can only ever be attached to one ThingServer, and each ThingServer corresponds to exactly one event loop. That means a mechanism may be introduced in the future that allows Thing code to access a blocking portal without the need for a dependency.

Functions

blocking_portal_from_thing_server(...)

Return the blocking portal from our ThingServer.

Module Contents

labthings_fastapi.dependencies.blocking_portal.blocking_portal_from_thing_server(request: fastapi.Request) → anyio.from_thread.BlockingPortal

Return the blocking portal from our ThingServer.

This is for use as a FastAPI dependency, to allow threaded code to call async code. See the module-level docstring for blocking_portal.

Parameters:

request – The fastapi.Request object, supplied by the Dependencies mechanism.

Returns:

the anyio.from_thread.BlockingPortal allowing access to the ThingServer‘s event loop.