import sys
IS_PY2 = sys.version_info < (3, 0)

if IS_PY2:
    from Queue import Queue
else:
    from queue import Queue

from threading import Thread


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 as e:
                # An exception happened in this thread
                print(e)
            finally:
                # Mark this task as done, whether an exception happened or not
                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 map(self, func, args_list, kwargs_list=None):
        """ Add a list of tasks to the queue """
        no_kwargs = kwargs_list is None
        inputs = args_list if no_kwargs else zip(args_list, kwargs_list)
        for inp in inputs:
            if no_kwargs:
                self.add_task(func, *inp)
            else:
                self.add_task(func, *inp[0], **inp[1])

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


if __name__ == "__main__":
    from random import randrange
    from time import sleep

    # Function to be executed in a thread
    def wait_delay(d, extra, kw=None):
        print("sleeping for (%d)sec" % d)
        print(kw)
        sleep(d)

    # Generate random delays and other arguments
    num_inp = 20
    delays = [[randrange(3, 7) for j in range(2)] for i in range(num_inp)]
    kwargs = [{'kw':7} for j in range(num_inp)]

    # Instantiate a thread pool with 5 worker threads
    pool = ThreadPool(5)

    # Add the jobs in bulk to the thread pool. Alternatively you could use
    # `pool.add_task` to add single jobs. The code will block here, which
    # makes it possible to cancel the thread pool with an exception when
    # the currently running batch of workers is finished.
    pool.map(wait_delay, delays, kwargs)
    pool.wait_completion()