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Concurrency to Channels
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Andrew Godwin
October 08, 2017
Programming
1
320
Concurrency to Channels
My keynote from Python Brasil 13 (2017).
Andrew Godwin
October 08, 2017
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Transcript
Andrew Godwin @andrewgodwin
Hi, I’m Andrew Godwin • Django core developer • Senior
Software Engineer at • South, Django migrations, Channels
What is Channels?
What is Channels?
Why Channels?
2000 2008 2015
Python 1.5 Threading 2000
Twisted 1.0 2002
WSGI (PEP 333) 2003
Python 2.6 Multiprocessing 2008
Django 1.0 2008
Eventlet / gevent 2009
Python 3.4 asyncio 2014
Python 3.5 async / await 2015
Web request handling is “solved” We have good patterns and
standards
Web request handling is easy It’s stateless, and has a
fixed response pattern
Client Server Request Response Process
Other protocols are not so easy Like WebSockets and MQTT
This is why they are more efficient No overheads of
cookies, headers and TCP handshake
Client Server Connect Data ??? Data Data Data
Writing async code is harder There’s a reason we don’t
do it all the time
Deadlocks Livelocks Race conditions Resource starvation
Simple Race Condition
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}
“Fixing” it, but actually adding a deadlock
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
Thread 1 Thread 2 get lock a get lock b
get lock b get lock a
More threads = more problems And hard to find in
development when you have no users
CSP “Communicating Sequential Processes” Algebra for talking about concurrency &
problems
You don’t need everything async Only the important bits
Channels: sync + async tooling Traditional synchronous Django with async
handling
“ASGI”: WSGI + async An interface that works for more
than request-response.
Goal: You mostly write sync code Channels/Django handles the annoying
part
Sync code for async behaviour
Why not just use asyncio? Do we need channels at
all?
Channels 1: Can’t write async code too Have to write
it separate outside of Channels framework
Channels 2: asyncio + sync support You can write code
as complex as you need to
Channels does not solve everything Neither does Django, the goal
is a good place to start
Working on more than just WebSocket Ways to write Django/Python
against anything with “events”
WebSockets? Emails? Chat? SMS?
What is Django in future? Is it HTTP requests forever?
Making async code easier = good Give people a way
to learn safely
Make Python the best place for these Even if it
doesn’t end up being Django.
Thanks. Andrew Godwin @andrewgodwin aeracode.org