Thread inside Application vs. Server process

I have a site which sometimes takes particularly long to process a request (and that's not a defect). 99% of the time it's pretty quick because it almost doesn't do any processing.

I want to show a message that says "Loading" when the site takes long to process the request. My site uses mod_wsgi and Apache. The way I see it, I would respond saying 'Loading' before completing the processing and do one of two things right before:

-spawn a (daemon) thread to take care of the processing.

-communicate through socket with other process and tell it to take care of the processing (most likely send request to http://localhost:8080/do_processing).

What are the pros and cons of one approach v开发者_Go百科s the other?

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Using a separate process is better. It does not have to be hard at all as suggested in another answer as you can use an existing system for doing exactly that such as Celery (http://celeryproject.org/). Relying on in process threads is not necessarily a good idea unless you are going to implement an internal job queueing system of your own to prevent blowing out of number of threads. Also, in a multiprocess server configuration you cant be guaranteed a request comes back to the same process and so not easy to get status of a running operation. Finally, the web server processes could get killed off and thus your background task could also be killed before it finishes. You would need to have a mechanism for holding state which can survive such an event if that was important. Far easier to use something like Celery.

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The process route requires quite a bit of a system processing. Creation of a separate process is relatively expensive and slow. However if your process crashes it doesn't affect your main governing process (you will receive the exit status code and will have an opportunity to respawn a new working process). You will also need some sort of InterProcessCommunication layer (can be a socket, pipe, shared memory, etc...) which is adds to complexity if your project.

Threads are lightweight and cheap. All you need to do is to manage concurrent access to shared resources. So it really depends on the task you have in mind. Threads probably will be more likely the appropriate way to implement your task.