Taking Django Async

A talk I gave at PyCon US 2018

Transcript

1. TAKING Andrew Godwin @andrewgodwin DJANGO ASYNC
2. Hi, I’m Andrew Godwin • Django core team member • Senior Software Engineer at • Does network programming for "fun"
3. 2015: Channels 0.1
4. Adds async protocol support to Django Headline protocol is WebSockets Also allows background jobs
5. 2017: Channels 1.0
6. Python 2.7 compatible Twisted for webserver Synchronous Django code
7. Webserver (Twisted) Django (Sync worker process) Client Channel Layer (Redis or other)
8. Webserver (Twisted) Django (Sync worker process) Clients Channel Layer (Redis or other) Webserver (Twisted) Django (Sync worker process)
9. Too many moving pieces No asyncio support Easy to shoot yourself in the foot
10. I was wrong.
11. 2018: Channels 2.0
12. Asyncio-native Python 3.5 and up Supports async coroutines and sync threads
13. Webserver (asyncio-native) Django (coroutines/threads) Client
14. Webserver (Twisted) Django (Sync worker process) Clients Webserver (Twisted) Django (Sync worker process) Channel Layer (Redis or other)
15. 75% rewrite
16. Async interfaces are separate to sync You can't provide both through one API
17. bit.ly/py-async-simp https://www.aeracode.org/2018/02/19/python-async-simplified/
18. Django had to be partially async
19. WSGI Handler (WSGI-to-request translator) URL Routing (path to view mapping) Django Middleware (auth, sessions, etc) Views (logic and presentation) ORM (database kerfuffling)
20. ASGI Handler (ASGI-to-request translator) URL Routing (path to view mapping) Django Middleware (auth, sessions, etc.) Views (logic and presentation) ORM (database kerfuffling)
21. ASGI Handler (ASGI-to-request translator) URL Routing (path to view mapping) Django Middleware (auth, sessions, etc.) Views (logic and presentation) ORM (database kerfuffling) ASGI Routing (path/protocol/etc. mapping) ASGI Middleware (auth, sessions, etc.) Consumers (logic and presentation) synchronous
22. Async-native most of the way
23. But how?
24. sync_to_async async_to_sync
25. sync_to_async async_to_sync
26. Synchronous code has to run in threads ThreadPoolExecutor does most of the hard work
27. loop = asyncio.get_event_loop() future = loop.run_in_executor( self.threadpool, func, ) return await future
28. Calling the ORM Rendering templates Handing off to Django views
29. sync_to_async async_to_sync
30. Async code runs on the event loop We need to go find it! Or make our own.
31. # Make a future for the return information call_result = Future() # Use call_soon_threadsafe to schedule a synchronous callback on the # main event loop's thread if not (self.main_event_loop and self.main_event_loop.is_running()): # Make our own event loop and run inside that. loop = asyncio.new_event_loop() asyncio.set_event_loop(loop) try: loop.run_until_complete(self.main_wrap(args, kwargs, call_result)) finally: try: if hasattr(loop, "shutdown_asyncgens"): loop.run_until_complete(loop.shutdown_asyncgens()) finally: loop.close() asyncio.set_event_loop(self.main_event_loop) else: self.main_event_loop.call_soon_threadsafe( self.main_event_loop.create_task, self.main_wrap( args, kwargs, call_result, ), ) # Wait for results from the future. return call_result.result()
32. Make a Future Jump to the main thread and add the coroutine Tie the coroutine's end to triggering the Future Block the thread on the Future
33. Lets us provide async-native APIs And still let synchronous code use them
34. Both async and sync code are useful Channels lets you write your code as both
35. ASGI Handler (ASGI-to-request translator) URL Routing (path to view mapping) Django Middleware (auth, sessions, etc.) Views (logic and presentation) ORM (database kerfuffling) ASGI Routing (path/protocol/etc. mapping) ASGI Middleware (auth, sessions, etc.) Consumers (logic and presentation) synchronous
36. How to make WSGI async?
37. ASGI: It's like WSGI but with an A in it Also asyncio and stuff like that
38. def application(environ, start_response): ... start_response(...) yield data
39. class Application: def __init__(self, scope): ... async def __call__(self, receive, send): event = await receive() ... await send(data)
40. "Turtles all the way down" Routing is an ASGI app. Middleware is too.
41. What does this mean for Django?
42. How much can we make async? Can we keep sync compatability?
43. What does an async ORM look like? Is it even a sensible endeavour?
44. Can we make Django more pluggable? Finally get to that shareable-middleware goal
45. Do we need to replace WSGI? Or does nobody want long-polling or websockets?
46. Multiple servers (daphne, uvicorn) Multiple frameworks (Django, …?)
47. Do we want to have everyone writing async? What's the balance? How do we be flexible enough?
48. What is Django?
49. Thanks. Andrew Godwin @andrewgodwin aeracode.org