Concurrency to Channels

My keynote from Python Brasil 13 (2017).

1. Andrew Godwin @andrewgodwin
2. Hi, I’m Andrew Godwin • Django core developer • Senior Software Engineer at • South, Django migrations, Channels
3. What is Channels?
4. What is Channels?
5. Why Channels?
6. 2000 2008 2015
7. Python 1.5 Threading 2000
8. Twisted 1.0 2002
9. WSGI (PEP 333) 2003
10. Python 2.6 Multiprocessing 2008
11. Django 1.0 2008
12. Eventlet / gevent 2009
13. Python 3.4 asyncio 2014
14. Python 3.5 async / await 2015
15. Web request handling is “solved” We have good patterns and standards
16. Web request handling is easy It’s stateless, and has a fixed response pattern
17. Client Server Request Response Process
18. Other protocols are not so easy Like WebSockets and MQTT
19. This is why they are more efficient No overheads of cookies, headers and TCP handshake
20. Client Server Connect Data ??? Data Data Data
21. Writing async code is harder There’s a reason we don’t do it all the time
22. Deadlocks Livelocks Race conditions Resource starvation
23. Simple Race Condition
24. Thread 1 Thread 2 if self.funds[..] < .. if self.funds[..] < .. self.funds[..] += .. self.funds[..] -= .. self.funds[..] += .. self.funds[..] -= .. {"a": 20, "b": 0} {"a": 0, "b": 20} {"a": -20, "b": 40}
25. “Fixing” it, but actually adding a deadlock
26. Thread 1 Thread 2 get lock a get lock b release lock b release lock a get lock b get lock a release lock a release lock b
27. Thread 1 Thread 2 get lock a get lock b get lock b get lock a
28. More threads = more problems And hard to find in development when you have no users
29. CSP “Communicating Sequential Processes” Algebra for talking about concurrency & problems
30. You don’t need everything async Only the important bits
31. Channels: sync + async tooling Traditional synchronous Django with async handling
32. “ASGI”: WSGI + async An interface that works for more than request-response.
33. Goal: You mostly write sync code Channels/Django handles the annoying part
34. Sync code for async behaviour
35. Why not just use asyncio? Do we need channels at all?
36. Channels 1: Can’t write async code too Have to write it separate outside of Channels framework
37. Channels 2: asyncio + sync support You can write code as complex as you need to
38. Channels does not solve everything Neither does Django, the goal is a good place to start
39. Working on more than just WebSocket Ways to write Django/Python against anything with “events”
40. WebSockets? Emails? Chat? SMS?
41. What is Django in future? Is it HTTP requests forever?
42. Making async code easier = good Give people a way to learn safely
43. Make Python the best place for these Even if it doesn’t end up being Django.
44. Thanks. Andrew Godwin @andrewgodwin aeracode.org