顺序流程的两个并行流程

Question

我有几个进程，例如A_step1，A_step2，B_step1，B_step2 ...它们必须以必须在step2开始运行之前必须完成step1的方式运行。 这是我所做的：

from subprocess import check_call
check_call(A_step1)
check_call(A_step2)
check_call(B_step1)
check_call(B_step2)

但是，我希望A和B进程并行运行。 无论如何，要在Python中实现这一目标？

非常感谢

Answer 1

您可能可以将相关进程放入函数中，然后异步运行它们。 对于异步部分，我建议使用多处理模块

Answer 2

一种常见的策略是使用队列作为一种机制，以允许协调员（通常是您的主要流程）分配工作，并作为一种方法，允许工人在完成某件事时告诉协调员。

这是一个简化的示例。 您可以尝试随机的睡眠时间，以说服自己，直到两个工作人员都完成了第一步的工作之后，才能开始第二步的工作。

from multiprocessing import Process, Manager
from time import sleep
from random import randint

def main():

    # Some queues so that we can tell the workers to advance
    # to the next step, and so that the workers to tell
    # us when they have completed a step.
    workQA = Manager().Queue()
    workQB = Manager().Queue()
    progQ = Manager().Queue()

    # Start the worker processes.
    pA = Process(target = workerA, args = (workQA, progQ))
    pB = Process(target = workerB, args = (workQB, progQ))
    pA.start()
    pB.start()

    # Step through some work.
    for step in (1, 2):
        workQA.put(step)
        workQB.put(step)
        done = []
        while True:
            item_done = progQ.get()
            print item_done
            done.append(item_done)
            if len(done) == 2:
                break

    # Tell the workers to stop and wait for everything to wrap up.
    workQA.put('stop')
    workQB.put('stop')
    pA.join()
    pB.join()

def workerA(workQ, progQ):
    do_work('A', workQ, progQ)

def workerB(workQ, progQ):
    do_work('B', workQ, progQ)

def do_work(worker, workQ, progQ):
    # Of course, in your real code the two workers won't
    # be doing the same thing.
    while True:
        step = workQ.get()
        if step == 1:
            do_step(worker, step, progQ)
        elif step == 2:
            do_step(worker, step, progQ)
        else:
            return

def do_step(worker, step, progQ):
    n = randint(1, 5)
    msg = 'worker={} step={} sleep={}'.format(worker, step, n)
    sleep(n)
    progQ.put(msg)   

main()

输出示例：

worker=B step=1 sleep=2
worker=A step=1 sleep=4
worker=A step=2 sleep=1
worker=B step=2 sleep=3