[FIXED] Make two competing functions and kill the slow one

Issue

In python, I have to fetch crypto data from binance every minute and do some calculations. For fetching data I have two functions func_a() and func_b(). They both do the same thing but in wildly different manner. Sometimes func_a is faster and sometimes func_b is faster. I want to run both the functions in parallel, if any of the function returns result to me faster, I want to kill the other one and move on (because they both are going to bring the same result).

How can I achieve this in python? Please mind that I do not want to replace these functions or their mechanics.

Solution

Python threads aren't very suitable for this purpose for two reasons:

1. The Python GIL means that if you spawn two CPU-bound threads, each of the two threads will run at half its normal speed (because only one thread is actually running at any given instant; the other is waiting to acquire the interpreter lock)
2. There is no reliable way to unilaterally kill a thread, because if you do that, any resources it had allocated will be leaked, causing major problems.

If you really want to be able to cancel a function-in progress, then, you have two options:

1. Modify the function to periodically check a "please_quit" boolean variable (or whatever) and return immediately if that boolean's state has changed to True. Then your main thread can set the please_quit variable and then call join() on the thread, and rest assured that the thread will quit ASAP. (This does require that you have the ability to modify the function's implementation)
2. Spawn child processes instead of child threads. A child process takes more resources to launch, but it can run truly in parallel (since it has its own separate Python interpreter) and it is safe (usually) to unilaterally kill it, because the OS will automatically clean up all of the process's held resources when the process is killed.

Answered By - Jeremy Friesner