Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Channels (Under The Hood)
Search
Andrew Godwin
November 03, 2016
Programming
1
7.5k
Channels (Under The Hood)
A talk I gave at Django Under The Hood 2016.
Andrew Godwin
November 03, 2016
Tweet
Share
More Decks by Andrew Godwin
See All by Andrew Godwin
Reconciling Everything
andrewgodwin
1
330
Django Through The Years
andrewgodwin
0
220
Writing Maintainable Software At Scale
andrewgodwin
0
450
A Newcomer's Guide To Airflow's Architecture
andrewgodwin
0
360
Async, Python, and the Future
andrewgodwin
2
680
How To Break Django: With Async
andrewgodwin
1
730
Taking Django's ORM Async
andrewgodwin
0
730
The Long Road To Asynchrony
andrewgodwin
0
660
The Scientist & The Engineer
andrewgodwin
1
780
Other Decks in Programming
See All in Programming
MCPでVibe Working。そして、結局はContext Eng(略)/ Working with Vibe on MCP And Context Eng
rkaga
5
2.3k
Performance for Conversion! 分散トレーシングでボトルネックを 特定せよ
inetand
0
3.6k
Swift Updates - Learn Languages 2025
koher
2
520
Putting The Genie in the Bottle - A Crash Course on running LLMs on Android
iurysza
0
140
速いWebフレームワークを作る
yusukebe
5
1.7k
Introducing ReActionView: A new ActionView-compatible ERB Engine @ Rails World 2025, Amsterdam
marcoroth
0
710
Things You Thought You Didn’t Need To Care About That Have a Big Impact On Your Job
hollycummins
0
110
AI Coding Agentのセキュリティリスク:PRの自己承認とメルカリの対策
s3h
0
240
テストコードはもう書かない:JetBrains AI Assistantに委ねる非同期処理のテスト自動設計・生成
makun
0
570
Flutter with Dart MCP: All You Need - 박제창 2025 I/O Extended Busan
itsmedreamwalker
0
150
🔨 小さなビルドシステムを作る
momeemt
4
690
今だからこそ入門する Server-Sent Events (SSE)
nearme_tech
PRO
3
260
Featured
See All Featured
RailsConf 2023
tenderlove
30
1.2k
Fantastic passwords and where to find them - at NoRuKo
philnash
52
3.4k
Fireside Chat
paigeccino
39
3.6k
"I'm Feeling Lucky" - Building Great Search Experiences for Today's Users (#IAC19)
danielanewman
229
22k
Improving Core Web Vitals using Speculation Rules API
sergeychernyshev
18
1.1k
XXLCSS - How to scale CSS and keep your sanity
sugarenia
248
1.3M
It's Worth the Effort
3n
187
28k
A Tale of Four Properties
chriscoyier
160
23k
GraphQLとの向き合い方2022年版
quramy
49
14k
Intergalactic Javascript Robots from Outer Space
tanoku
272
27k
How to Ace a Technical Interview
jacobian
279
23k
Helping Users Find Their Own Way: Creating Modern Search Experiences
danielanewman
29
2.9k
Transcript
None
Andrew Godwin Hi, I'm Django core developer Senior Software Engineer
at Used to complain about migrations a lot
It's magic.
It's magic.
The Problem 1
The Web is changing.
WebSockets
WebSockets WebRTC Long-polling MQTT Server-Sent Events
Python is synchronous. Django is synchronous.
Synchronous code is easier to write. Single-process async is not
enough.
Proven design pattern Not too hard to reason about
What could fit these constraints?
Loose Coupling 2
Not too tied to WebSockets Not too tied to Django
Well-defined, minimal interfaces
Easy to swap out or rewrite
The Message Bus HTTP Server Message Bus WSock Server Django
Project
What do you send? How do you send it?
ASGI
nonblocking send blocking receive add to group discard from group
send to group
JSON-compatible, dictionary-based messages onto named channels
Concrete Ideas 3
Develop using concrete examples
WebSocket connect receive disconnect accept/reject send
WebSocket websocket.connect websocket.send!abc1234 websocket.receive websocket.disconnect
At-most-once First In First Out Backpressure via capacity Not sticky
No guaranteed ordering No serial processing
HTTP & WS Channel Layer Django Worker HTTP & WS
Django Worker Django Worker Django Worker
{ "text": "Hello, world!", "path": "/chat/socket/", "reply_channel": "websocket.send!9m12in2p", }
Developed and spec'd HTTP WebSocket Rough drafts IRC Email Slack
Please, no. Minecraft Mainframe Terminal
{ "reply_channel": "http.response!g23vD2x5", "method": "GET", "http_version": "2", "path": "/chat/socket/", "query_string":
"foo=bar", "headers": [["cookie", "abcdef..."]], }
At-most-once First In First Out Backpressure via capacity Not sticky
No guaranteed ordering No serial processing
At-most-once First In First Out Backpressure via capacity Not sticky
No guaranteed ordering No serial processing
"order" key on receive messages Connection acceptance
Daphne HTTP/WebSocket Server Channels Django integration asgi-redis Redis backend asgi-ipc
Local memory backend asgiref Shared code and libs
Django-ish 4
It can take several tries to get a nice API.
Consumers based on Views Callable that takes an object Decorators
for functionality Class-based generics
@channel_session def chat_receive(message): name = message.channel_session["name"] message.reply_channel.send({"text": "OK"}) Group("chat").send({ "text":
"%s: %s" % (name, message["text"]), }) Message.objects.create( name=name, content=message["text"], )
Routing based on URLs List of regex-based matches Includes with
prefix stripping on paths More standardised interface
routing = [ route( "websocket.receive", consumers.chat_receive, path=r"^/chat/socket/$", ), include("stats.routing", path="^/stats/"),
route_class(ConsumerClass, path="^/v1/"), ]
Sessions are the only state Sessions hang off reply channels
not cookies Uses same sessions backends Available on the consumer's argument Can also access long-term cookie sessions
@enforce_ordering def receive_consumer(message): Log.objects.create(...)
session = session_for_reply_channel( message.reply_channel.name ) if not session.exists(session.session_key): try: session.save(must_create=True)
except CreateError: # Session wasn't unique raise ConsumeLater() message.channel_session = session
No Middleware New-style middleware half works No ability to capture
sends Decorators replace most cases
View/HTTP Django still there Can intermingle or just use one
type View system is just a consumer now
def view_consumer(message): replies = AsgiHandler()(message) for reply in replies: while
True: try: message.reply_channel.send(reply) except ChannelFull: time.sleep(0.05) else: break
Signals and commands runserver works as expected Signals for handling
lifecycle staticfiles configured for development
Beyond 5
Generalised async communication
Service messaging Security/CPU separation Sync & Async / Py2 &
Py3
Diversity of implementations More web servers More channel layers
More optimisation More efficient bulk sends Less network traffic on
receive
More maintainers More viewpoints, more time
1.0 coming soon Stable APIs for everything except binding
Thanks. Andrew Godwin @andrewgodwin channels.readthedocs.io github.com/andrewgodwin/channels-examples