Parallelism in one web request

Question

Our server has a lot if CPUs, and some web requests could be faster if request handlers would do some parallel processing.

Example: Some work needs to be done on N (about 1-20) pictures, to severe one web request.

Caching or doing the stuff before the request comes in is not possible.

What can be done to use several CPUs of the hardware:

• threads: I don't like them
• multiprocessing: Every request needs to start N processes. Many CPU cycles will be lost for starting a new process and importing libraries.
• special (hand made) service, which has N processes ready for processing
• cellery (rabbitMQ): I don't know how big the communication overhead is...
• Other solution?

Platform: Django (Python)

Answer 1

Regarding your second and third alternatives: you do not need to start a new process for every request. This is what process pools are for. New processes are created when your app starts up. When you submit a request to the pool, it is automatically queued until a worker is available. The disadvantage is that requests are blocking- if no worker is available at the moment, your user will sit and wait.

Answer 2

You could use the standard library module asyncore.

This module provides the basic infrastructure for writing asynchronous socket service clients and servers.

There is an example for how to create a basic HTML client.

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Then there's Twisted, it can do lots and lots of things, which is why it's somewhat daunting. Here is an example using its HTTP client.

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Twisted "speaks HTTP", asyncore does not, you'll have to.

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Other libraries:

• Tornado's httpclient
• asynchttp