在 Python 中，如何使用多处理从特定进程取回数据? [英] In Python, how do you get data back from a particular process using multiprocessing?

问题描述

import multiprocessing as mp
import time

def build(q):
    print 'I build things'
    time.sleep(10)
    #return 42
    q.put(42)

def run(q):
    num = q.get()
    print num

    if num == 42:
        print 'I run after build is done'
        return
    else:
        raise Exception("I don't know build..I guess")

def get_number(q):
    q.put(3)

if __name__ == '__main__':
    queue = mp.Queue()

    run_p = mp.Process(name='run process', target=run, args=(queue,))
    build_p = mp.Process(name='build process', target=build, args=(queue,))
    s3 = mp.Process(name='s3', target=get_number, args=(queue,))

    build_p.start()
    run_p.start()
    s3.start()

    print 'waiting on build'
    build_p.join(1) # timeout set to 1 second
    s3.join()

    print 'waiting on run'
    run_p.join()

    queue.close()
    print 'waiting on queue'
    queue.join_thread()
    print 'done'

我的目标是将 build 和 run 发送到不同的 worker，并且 run 必须从 build 返回结果代码> 以继续.

My goal is to send build and run into different workers, and run has to get result back from build in order to proceed.

以上根据您的帮助修改后的代码实际上会返回异常，因为 s3 在 build 有机会之前返回.

The above revised code based on your help will actually return exception, because s3 is returned before build has the chance.

队列前面的值现在是 3.我们如何确保从 build 过程中得到答案?

The value in the front of the queue is now 3. How can we make sure we get the answer back from build process?

谢谢.

推荐答案

你的问题有点含糊.你描述的问题听起来是同步的，所以 3 个进程有点矫枉过正.

Your question is a little murky..the problem you are describing sounds synchronous so 3 processes are a little overkill.

假设您只是尝试传递值以运行，您可以使用队列对象.

Assuming you are just trying to pass values to run you could use the queue object.

import multiprocessing as mp
import time

def build(q):
    print 'I build things'
    time.sleep(5)
    q.put(42)
    return 

def run(q):
    while True:
        num = q.get()
        if num == 42:
            print 'I run after build is done'
            return
        else:
            print 'not the right number...'

    def get_number():
        return 41

if __name__ == '__main__':
    queue = mp.Queue()

    run_p = mp.Process(name='run process', target=run, args=(queue,))
    build_p = mp.Process(name='build process', target=build, args=(queue,))

    run_p.start()
    build_p.start()

    print 'waiting on build'
    build_p.join()
    print 'waiting on run'
    run_p.join()
    queue.close()
    print 'waiting on queue'
    queue.join_thread()
    print 'done'

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