CODEWITHSUNDEEP
pythonmultithreadingblockingqueue
Vincent Beltman
Vincent Beltman

Reputation: 2112

What happens with a thread if it's in a infinite while loop python

I found this article about queue's in python: http://www.blog.pythonlibrary.org/2012/08/01/python-concurrency-an-example-of-a-queue/

It works fine but I have question about it. In the run method of the thread we see:

def run(self):
    while True:
        # gets the url from the queue
        url = self.queue.get()

        # download the file
        self.download_file(url)

        # send a signal to the queue that the job is done
        self.queue.task_done()

The thread is in a infinite while-loop without calling break. What happens to this thread when the program ends?

Upvotes: 1

Views: 580

Answers (1)

dano
dano

Reputation: 94961

It depends on what you mean by "the program ends". If the main thread just reaches the end of its execution, there are two possibilities:

  1. If the thread is a non-daemon threading.Thread, the running thread will keep the program alive indefinitely.

  2. If the thread is a daemon, the thread will be abruptly terminated as soon as the main thread ends.

The daemon property is described in the docs like this:

A boolean value indicating whether this thread is a daemon thread (True) or not (False). This must be set before start() is called, otherwise RuntimeError is raised. Its initial value is inherited from the creating thread; the main thread is not a daemon thread and therefore all threads created in the main thread default to daemon = False.

The entire Python program exits when no alive non-daemon threads are left.

If by "program ends" you mean the process gets a SIGTERM or SIGKILL or something similar, then the thread will terminate along with the rest of the program, even if its not a daemon.

Upvotes: 2

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