Async Task Channels Demo
It is split up into a few different step with tags so you can more easily see how it was built up.
git clone https://github.com/albertoconnor/asyncdemo.git cd asyncdemo git checkout step1
At this point, the code is for a basic Django 1.10 web app. Get into your favorite type of virtual env and then run the following.
pip install -r requirements.text cd asyncdemo python manage.py migrate python manage.py runserver
Now you should have the hello_view being served at http://127.0.0.1:8000/. You can append "?name=yourname" to change the name displayed.
Meanwhile, there is a simulated slow network call which writes out the hello message to the console and takes between 5 and 30 seconds to do it.
git checkout step2 python manage.py runserver
This has updated requirements.txt and settings.py and created a routes.py which is even to get Django to run with Channels. The view remains unchanged, so it will still be slow when you runserver. You can see though the output Django produces when you runserver has been changed.
git checkout step3 python manage.py runserver
A "notify" channel has been declared and the view now uses it. When you runserver the website is more responsive, but if you hammer it those slow 30 second simulated network calls will gum up the system.
git checkout bonusround
This changes channels to use redis as the broker of messages. Even to runserver you will need to have redis running locally.
When you do you will get the same behavior of step 3. To get around the slow down under load we will need to run everything in separate processes, in separate terminals.
daphne asyncdemo.asgi:channel_layer --port 8000
This runs the interface server in it's own process. If you try to connect now it will time out because there are no workers running.
You can run workers in as many separate terminals as you like:
python manage.py runworker
But the key to trying to maintain throughput is to run a worker which will never be tied up with a notification task:
python manage.py runworker --exclude-channels=notify
This worker will ensure that hello_view remains responsive.