[SOLVED] How can I stop the execution of a Python function from outside of it?

Issue

So I have this library that I use and within one of my functions I call a function from that library, which happens to take a really long time. Now, at the same time I have another thread running where I check for different conditions, what I want is that if a condition is met, I want to cancel the execution of the library function.

Right now I’m checking the conditions at the start of the function, but if the conditions happen to change while the library function is running, I don’t need its results, and want to return from it.

Basically this is what I have now.

def my_function():
    if condition_checker.condition_met():
        return
    library.long_running_function()

Is there a way to run the condition check every second or so and return from my_function when the condition is met?

I’ve thought about decorators, coroutines, I’m using 2.7 but if this can only be done in 3.x I’d consider switching, it’s just that I can’t figure out how.

Solution

You cannot terminate a thread. Either the library supports cancellation by design, where it internally would have to check for a condition every once in a while to abort if requested, or you have to wait for it to finish.

What you can do is call the library in a subprocess rather than a thread, since processes can be terminated through signals. Python’s multiprocessing module provides a threading-like API for spawning forks and handling IPC, including synchronization.

Or spawn a separate subprocess via subprocess.Popen if forking is too heavy on your resources (e.g. memory footprint through copying of the parent process).

I can’t think of any other way, unfortunately.

Answered By – twiebe

Answer Checked By – Mildred Charles (BugsFixing Admin)

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