A single worker with queue and promise pattern (inspiration from Javascript)

worker.py

from Queue import Queue
from threading import Thread

'''
A single worker with queue and promise pattern
usage: worker.add_job(fn).then(callback_fn)

note: this might be anti-pattern
'''

class Promise:

    def __init__(self):
        self.val = None
        self.success = False
        self.callback = None

    def done(self, value):
        # print('job done:', value)
        self.val = value
        if self.callback:
            self.callback(value)

    def then(self, callback):
        self.callback = callback

    def is_ready(self):
        return self.success is True

class Worker:

    def __init__(self, cnt=1):
        self.queue = Queue()
        self.threads = self._init_threads(cnt)
        self.results = []

    def add_job(self, fn):
        promise = Promise()
        self.queue.put((len(self.results), fn, promise))
        self.results.append(None)
        return promise

    def close(self):
        self.queue.join()
        return self.results

    def _worker(self):
        while True:
            i, fn, promise = self.queue.get()
            # print('new job:', item)
            r = fn()
            self.results[i] = r
            promise.done(r)
            self.queue.task_done()

    def _init_threads(self, cnt):
        threads = []
        for i in range(cnt):
            thread = Thread(target=self._worker)
            threads.append(thread)
            thread.daemon = True
            thread.start()
        return threads