Python multiprocessing processes sleep after a while

As @Felipe-Lema pointed out it is a classical RTFM.

I reworked the mentioned part of the script using a multiprocessing Queue instead of a Pool and improved the runtime:

def check_files(file_list):
    """Checks and replaces lines in files
    @param file_list: list of files to search
    @return counter: number of occurrence """

    # as much workers as CPUs are available (HT included)
    workers = multiprocessing.cpu_count()

    # create two queues: one for files, one for results
    work_queue = Queue()
    done_queue = Queue()
    processes = []

    # add every file to work queue
    for filename in file_list:
        work_queue.put(filename)

    # start processes
    for w in xrange(workers):
        p = Process(target=worker, args=(work_queue, done_queue))
        p.start()
        processes.append(p)
        work_queue.put('STOP')

    # wait until all processes finished
    for p in processes:
        p.join()

    done_queue.put('STOP')

    # beautify results and return them
    results = []
    for status in iter(done_queue.get, 'STOP'):
        if status is not None:
             results.append(status)

     return results