asgiref

• https://github.com/django/asgiref

ASGI:

• ASGI is a standard for Python asynchronous web apps and servers to communicate with each other,
• and positioned as an asynchronous successor to WSGI.
• You can read more at https://asgi.readthedocs.io/en/latest/

This package includes ASGI base libraries, such as:

• Sync-to-async and async-to-sync function wrappers, asgiref.sync
• Server base classes, asgiref.server
• A WSGI-to-ASGI adapter, in asgiref.wsgi

Function wrappers

These allow you to wrap or decorate async or sync functions to call them from the other style (so you can call async functions from a synchronous thread, or vice-versa).

In particular:

• AsyncToSync lets a synchronous subthread stop and wait while the async function is called on the main thread’s event loop, and then control is returned to the thread when the async function is finished.
• SyncToAsync lets async code call a synchronous function, which is run in a threadpool and control returned to the async coroutine when the synchronous function completes.

Easy to Call:

• The idea is to make it easier to call synchronous APIs from async code and asynchronous APIs from synchronous code
• so it’s easier to transition code from one style to the other.
• In the case of Channels, we wrap the (synchronous) Django view system with SyncToAsync to allow it to run inside the (asynchronous) ASGI server.

Note:

• Note that exactly what threads things run in is very specific, and aimed to keep maximum compatibility with old synchronous code.
• See “Synchronous code & Threads” below for a full explanation.
• By default, sync_to_async will run all synchronous code in the program in the same thread for safety reasons;
• you can disable this for more performance with @sync_to_async(thread_sensitive=False),
• but make sure that your code does not rely on anything bound to threads (like database connections) when you do.

Threadlocal replacement

asgiref.local:

• This is a drop-in replacement for threading.local that works with both threads and asyncio Tasks.
• Even better, it will proxy values through from a task-local context to a thread-local context
• when you use sync_to_async to run things in a threadpool, and vice-versa for async_to_sync.
• If you instead want true thread- and task-safety, you can set thread_critical on the Local object to ensure this instead.

記事:

• Why is using thread locals in Django bad?

Server base classes

Includes a StatelessServer class which provides all the hard work of writing a stateless server (as in, does not handle direct incoming sockets but instead consumes external streams or sockets to work out what is happening).

An example of such a server would be a chatbot server that connects out to a central chat server and provides a “connection scope” per user chatting to it. There’s only one actual connection, but the server has to separate things into several scopes for easier writing of the code.

You can see an example of this being used in frequensgi.

WSGI-to-ASGI adapter

• Allows you to wrap a WSGI application so it appears as a valid ASGI application.

• Simply wrap it around your WSGI application like so:

  asgi_application = WsgiToAsgi(wsgi_application)

• The WSGI application will be run in a synchronous threadpool,

• and the wrapped ASGI application will be one that accepts http class messages.

• Please note that not all extended features of WSGI may be supported (such as file handles for incoming POST bodies).