Monitoring thread function.

    Checks if thread is hanging for time defined by
    ``seconds_frozen`` parameter every ``test_interval`` milliseconds.

def monitor(seconds_frozen, test_interval):
    """Monitoring thread function.

    Checks if thread is hanging for time defined by
    ``seconds_frozen`` parameter every ``test_interval`` milliseconds.
    """
    current_thread = threading.current_thread()
    hanging_threads = set()
    old_threads = {}  # Threads found on previous iteration.

    while not current_thread.is_stopped():
        new_threads = get_current_frames()

        # Report died threads.
        for thread_id in old_threads.keys():
            if thread_id not in new_threads and thread_id in hanging_threads:
                log_died_thread(thread_id)

        # Process live threads.
        time.sleep(test_interval/1000.)
        now = time.time()
        then = now - seconds_frozen
        for thread_id, thread_data in new_threads.items():
            # Don't report the monitor thread.
            if thread_id == current_thread.ident:
                continue
            frame = thread_data['frame']
            # If thread is new or it's stack is changed then update time.
            if (thread_id not in old_threads or
                    frame != old_threads[thread_id]['frame']):
                thread_data['time'] = now
                # If the thread was hanging then report awaked thread.
                if thread_id in hanging_threads:
                    hanging_threads.remove(thread_id)
                    log_awaked_thread(thread_id)
            else:
                # If stack is not changed then keep old time.
                last_change_time = old_threads[thread_id]['time']
                thread_data['time'] = last_change_time
                # Check if this is a new hanging thread.
                if (thread_id not in hanging_threads and
                        last_change_time < then):
                    # Gotcha!
                    hanging_threads.add(thread_id)
                    # Report the hanged thread.
                    log_hanged_thread(thread_id, frame)
        old_threads = new_threads