收听列表并在附加时做某事

Question

我有一个 API 侦听传入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 Process
import time

procs = []

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: 1
length of the list from separate Process: 0
length of the list from main: 2
length of the list from separate Process: 0
length of the list from separate Process: 0
length of the list from main: 3
length of the list from separate Process: 0
length 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的副本 space，但不会反映任何后续更改（由父进程或子进程进行）在另一个进程的内存中。他们每个人都有自己的私人地址 space.

您可以改为创建 Manager() and use its shared list 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 Manager 服务器。

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()

收听列表并在附加时做某事

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python-3.x

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收听列表并在附加时做某事