Python threads are not being garbage collected

Question

Here is my threading setup. On my machine the maximum number of threads is 2047.

class Worker(Thread):
    """Thread executing tasks from a given tasks queue"""
    def __init__(self, tasks):
        Thread.__init__(self)
        self.tasks = tasks
        self.daemon = True
        self.start()

    def run(self):
        while True:
            func, args, kargs = self.tasks.get()
            try:
                func(*args, **kargs)
            except Exception, e:
                print e
            self.tasks.task_done()

class ThreadPool:
    """Pool of threads consuming tasks from a queue"""
    def __init__(self, num_threads):
        self.tasks = Queue(num_threads)
        for _ in range(num_threads):
            Worker(self.tasks)

    def add_task(self, func, *args, **kargs):
        """Add a task to the queue"""
        self.tasks.put((func, args, kargs))

    def wait_completion(self):
        """Wait for completion of all the tasks in the queue"""
        self.tasks.join()

In other classes in my module, I call the ThreadPool class from above to create a new pool of threads. I then perform operations. Here is an example:

def upload_images(self):
    '''batch uploads images to s3 via multi-threading'''
    num_threads = min(500, len(pictures))
    pool = ThreadPool(num_threads)

    for p in pictures:
        pool.add_task(p.get_set_upload_img)

    pool.wait_completion()

The problem I am having is that these threads are not being garbage collected.

After a few runs, here is my error:

File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 495, in start _start_new_thread(self.__bootstrap, ()) thread.error: can't start new thread

Which means I have hit the thread limit of 2047.

Any ideas? Thanks.

Answer 1

Your worker thread never returns from run, so your thread never ends.

Perhaps something like the following for your run method?

def run(self):
    while True:
        try:
            func, args, kargs = self.tasks.get()
        except Queue.Empty:
            break

        try:
            func(*args, **kargs)
        except Exception, e:
            print e

        self.tasks.task_done()