Python3 多线程函数返回值

第一种写法，多进程的函数是没有返回值的，需要放在Queue中来取值

import multiprocessing as mp

def job(char, num, q):
    q.put([char] * num)

if __name__ == "__main__":
    q = mp.Queue()
    p1 = mp.Process(target=job, args=("a", 3, q))
    p2 = mp.Process(target=job, args=("b", 4, q))
    p1.start()
    p2.start()
    p1.join()
    p2.join()
    print(q.get())
    print(q.get())

join()用于等待子进程退出，输出为

['b', 'b', 'b', 'b']
['a', 'a', 'a']

第二种写法，线程池

import multiprocessing as mp

def job(char, num):
    return [char] * num

if __name__ == "__main__":
    with mp.Pool(processes=mp.cpu_count() - 1) as pool:
        p1 = pool.apply_async(job, ('a', 3))
        p2 = pool.apply_async(job, ('b', 4))
        print(p1.get(timeout=1))
        print(p2.get(timeout=1))

输出类似

['a', 'a', 'a']
['b', 'b', 'b', 'b']

其中这个pool.join()要不要加好像不要紧，参考这个回答when-should-we-call-multiprocessing-pool-join
第三种写法：

import multiprocessing as mp

def job(char, num):
    return [char] * num

if __name__ == "__main__":
    args = [("a", 4), ("b", 3)]
    with mp.Pool(processes=mp.cpu_count() - 1) as pool:
        results = pool.starmap(job, args)
    print(results)

返回值

[['a', 'a', 'a', 'a'], ['b', 'b', 'b']]

非常类似的写法：

import multiprocessing as mp

def job(char, num):
    return [char] * num

if __name__ == "__main__":
    args = [("a", 4), ("b", 3)]
    with mp.Pool(processes=mp.cpu_count() - 1) as pool:
        results = pool.starmap_async(job, args)
        print(results.get(timeout=1))

参考文献

stackoverflow: python multiprocessing pool map for multiple arguments
https://docs.python.org/3/library/multiprocessing.html