Python Multiprocess Pool. How to exit the script when one of the worker process determines no more work needs to be done?

Question

mp.set_start_method(\'spawn\')
total_count = Counter(0)
pool = mp.Pool(initializer=init, initargs=(total_count,), processes=num_proc)    

pool.map(part_crack_helper         


        

Answer 1

You can use callbacks from Pool.apply_async.

Something like this should do the job for you.

from multiprocessing import Pool


def part_crack_helper(args):
    solution = do_job(args)
    if solution:
        return True
    else:
        return False


class Worker():
    def __init__(self, workers, initializer, initargs):
        self.pool = Pool(processes=workers, 
                         initializer=initializer, 
                         initargs=initargs)

    def callback(self, result):
        if result:
            print "Solution found! Yay!"
            self.pool.terminate()

    def do_job(self):
        for args in product(seed_str, repeat=4):
            self.pool.apply_async(part_crack_helper, 
                                  args=args, 
                                  callback=self.callback)

        self.pool.close()
        self.pool.join()
        print "good bye"


w = Worker(num_proc, init, [total_count])
w.do_job()

Answer 2

If you are ok with using another library, you could solve it the following way with Pebble. The advantage of this solution is that you can additionally specify a timeout. That means either the program ends if there is one successful worker or if it runs out of time:

from pebble import ProcessPool, ProcessExpired
from concurrent.futures import TimeoutError
import time

pool = ProcessPool()

def my_function(args):
    print("running " + str(args))
    time.sleep((args + 1) * 30)
    print("process won:" + str(args))
    return True


start_time = time.time()

future = pool.map(my_function, range(4), timeout=65)
iterator = future.result()

while True:
    try:
        result = next(iterator)
        if result:
            pool.stop()
            pool.join(timeout=0)
            break
    except StopIteration:
        break
    except TimeoutError as error:
        print("function took longer than %d seconds" % error.args[1])
    except ProcessExpired as error:
        print("%s. Exit code: %d" % (error, error.exitcode))
    except Exception as error:
        print("function raised %s" % error)
        print(error.traceback)  # Python's traceback of remote process

print("whole time: " + str(time.time() - start_time))