#!/usr/bin/python3

import queue
import threading


class SingleThreadTaskRunner():
    """
    A task runner that runs tasks in the same sequence they were added
    on a single thread.

    Its main advantage is that you can safely add tasks from various
    threads and there will not be any races between those tasks.

    Example:
        runner = SingleThreadTaskRunner(10)
        while True:
            runner.add_task(function_name, arg1, arg2)
    """

    def __init__(self, max_queued_tasks):
        self.queue = queue.Queue(max_queued_tasks)
        self.thread = threading.Thread(target=self.worker)
        self.thread.daemon = True
        self.thread.start()

    def worker(self):
        while True:
            item = self.queue.get()
            if item is None:
                break
            task, args, kwargs = item
            task(*args, **kwargs)
            self.queue.task_done()

    def add_task(self, task, *args, **kwargs):
        args = args or ()
        kwargs = kwargs or {}
        self.queue.put((task, args, kwargs))

    def join(self):
        self.running = False
        self.queue.put(None)
        self.thread.join()