收听列表​​并在附加时做某事

Question

我有一个 API 监听传入的请求并将它们转储到列表中。在一个单独的过程中，我想在附加列表时触发某种操作。我尝试实例化一个新进程（来自多处理），但它不会在启动后更新数组的状态。from multiprocessing import Processimport timeprocs = []def separateProcess(start, counter):    while True:        time.sleep(1)        print("length of the list from separate Process: "+str(len(procs)))if __name__ == '__main__':    print("program started")    counter = 0    Process(target=separateProcess, args=(counter, counter)).start()    print("program end")    while True:        counter += 1        newstring = "string "+str(counter)        procs.append(newstring)        print("length of the list from main: " + str(len(procs)))        time.sleep(2)这是输出：length of the list from main: 1length of the list from separate Process: 0length of the list from main: 2length of the list from separate Process: 0length of the list from separate Process: 0length of the list from main: 3length of the list from separate Process: 0length of the list from separate Process: 0

Answer 1

创建新的子进程时，它会获得父进程地址空间的副本，但是任何后续更改（无论是父进程还是子进程）都不会反映在其他进程的内存中。他们每个人都有自己的私人地址空间。

您可以创建一个Manager()并改用其共享列表对象：

import time

  

from multiprocessing import Manager, Process

def separateProcess(start, counter):

    while True:

        time.sleep(1)

        print("length of the list from separate Process: "+str(len(procs)))

if __name__ == '__main__':

    m = Manager()

    procs = m.list()

    print("program started")

    counter = 0

    Process(target=separateProcess, args=(counter, counter)).start()

    print("program end")

    while True:

        counter += 1

        newstring = "string "+str(counter)

        procs.append(newstring)

        print("length of the list from main: " + str(len(procs)))

        time.sleep(2)

这种方法有一些开销，因为它会产生一个子进程来托管服务器Manager。

如果您可以调整工作进程逻辑以改为使用队列，这里有一个示例：

import random

import time

from multiprocessing import cpu_count, Process, Queue

def worker(q):

    for item in iter(q.get, 'STOP'):

        t = random.uniform(1, 5)

        print(f'START item: {item}')

        time.sleep(t)

        print(f'END item: {item}, ({t:.3f}s)')

def main():

    cpus = cpu_count()

    q = Queue()

    for i in range(5):

        q.put(i)

    for i in range(cpus):

        Process(target=worker, args=(q,)).start()

    for i in range(cpus):

        q.put('STOP')

if __name__ == '__main__':

    main()