Threads + Futures in Python

threads-futures.py

'''
Pros: 
- Get the spawned thread (use thread.join() to wait on it, for example)
- Get the future
- Calling worker.future.result() will automatically raise an exception in the main thread
'''

from concurrent.futures import Future
import threading
import time

def test():
    time.sleep(2)
    return 'test'
    raise Exception('foo')

class Worker(object):
    def __init__(self, fn, args=()):
        self.future = Future()
        self._fn = fn
        self._args = args
    
    def start(self, cb=None):
        self._cb = cb
        self.future.set_running_or_notify_cancel()
        thread = threading.Thread(target=self.run, args=())
        thread.daemon = True #this will continue thread execution after the main thread runs out of code - you can still ctrl + c or kill the process
        thread.start()
        return thread

    def run(self):
        try:
            self.future.set_result(self._fn(*self._args))
        except BaseException as e:
            self.future.set_exception(e)
        
        if(self._cb):
            self._cb(self.future.result())


worker = Worker(test)
thread = worker.start(lambda x: print('callback', x))

while True:
    print("waiting")
    if worker.future.done():
        exc = worker.future.exception()
        print('exception?', exc)
        result = worker.future.result()
        print('result', result)
            
        break
    time.sleep(0.25)