Question

what i want to do is be able to call a function with multiple threads and get their results.

i have the following code:

(it is an example, the actual code doesn’t simply convert str to int)

from threading import Thread
import time
import Queue

#an example - actual code connects to a server
def str_to_int(arg, queue):
    result = 0
    result = int(arg)
    #sleep to check that they happen at once.
    time.sleep(10)
    queue.put(result)

def combine():
    q1 = Queue.Queue()
    q2 = Queue.Queue()
    q3 = Queue.Queue()

    t1 = Thread(target = str_to_int, args=("111", q1))
    t2 = Thread(target = str_to_int, args=("222", q2))
    t3 = Thread(target = str_to_int, args=("333", q3))

    t1.start()
    t2.start()
    t3.start()

    t1.join()
    t2.join()
    t3.join()

    return (q1.get(),q2.get(),q3.get())

print combine()

this code works. and i get the expected results:

>>> 
(111, 222, 333)

however, there must be a better way to do this.
i plan on having many more threads than 3, but even if i was only staying with 3 – it seems very ugly.

EDIT: i need to be able to know which result came from which thread (ie: from which parameters/arguments that i gave the function)

Answer 1

Here are some advices:

1. Queue‘s are thread-safe, so use 1 queue to pass results.
2. You can create all threads in a cycle and use your queue to pass results. You don’t need to have explicit variable for each thread.

So here’s what your code might look like:

def str_to_int(arg, queue):
    result = int(arg)
    queue.put({arg: result})

def combine():
    arguments = ('111', '222', '333')
    q = Queue.Queue()
    threads = []

    for argument in arguments:
        t = Thread(target=str_to_int, args=(argument, q))
        t.start()
        threads.append(t)

    for t in threads:
        t.join()

    return [q.get() for _ in xrange(len(arguments))]