Python thread exit code

Question

Is there a way to tell if a thread has exited normally or because of an exception?

Answer 1

Have your thread function catch exceptions. (You can do this with a simple wrapper function that just calls the old thread function inside a try...except or try...except...else block). Then the question just becomes "how to pass information from one thread to another", and I guess you already know how to do that.

Answer 2

As mentioned, a wrapper around the Thread class could catch that state. Here's an example.

>>> from threading import Thread
>>> class MyThread(Thread):
    def run(self):
        try:
            Thread.run(self)
        except Exception as err:
            self.err = err
            pass # or raise err
        else:
            self.err = None


>>> mt = MyThread(target=divmod, args=(3, 2))
>>> mt.start()
>>> mt.join()
>>> mt.err
>>> mt = MyThread(target=divmod, args=(3, 0))
>>> mt.start()
>>> mt.join()
>>> mt.err
ZeroDivisionError('integer division or modulo by zero',)

Answer 3

You could set some global variable to 0 if success, or non-zero if there was an exception. This is a pretty standard convention.

However, you'll need to protect this variable with a mutex or semaphore. Or you could make sure that only one thread will ever write to it and all others would just read it.