Should I use fork or threads?

Question

In my script, I have a function foo which basically uses pynotify to notify user about something repeatedly after a time interval say 15 minutes.

def foo:
    while True:
        """Does something"""
        time.sleep(900)

My main script has to interact with user & does all other things so I just cant call the foo() function. directly.

Whats the better way of doing it and why? Using fork or threads?

Answer 1

I won't tell you which one to use, but here are some of the advantages of each:

Threads can start more quickly than processes, and threads use fewer operating system resources than processes, including memory, file handles, etc. Threads also give you the option of communicating through shared variables (although many would say this is more of a disadvantage than an advantage - See below).

Processes each have their own separate memory and variables, which means that processes generally communicate by sending messages to each other. This is much easier to do correctly than having threads communicate via shared memory. Processes can also run truly concurrently, so that if you have multiple CPU cores, you can keep all of them busy using processes. In Python^*, the global interpreter lock prevents threads from making much use of more than a single core.

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^* - That is, CPython, which the implementation of Python that you get if you go to http://python.org and download Python. Other Python implementations (such as Jython) do not necessarily prohibit Python from running threads on multiple CPUs simultaneously. Thanks to @EOL for the clarification.

Answer 2

For these kinds of problems, neither threads nor forked processes seem the right approach. If all you want to do is to once every 15 minutes notify the user of something, why not use an event loop like GLib's or Twisted's reactor ? This allows you to schedule operations that should run once in a while, and get on with the rest of your program.