在Python中终止进程

Question

我对python中的MultiProcessing这个概念还不熟悉。

我有这个代码

import os, time
from multiprocessing import Process, current_process


def square(number):
    """The function squares whatever number it is provided."""
    result = number * number

    # We can use the OS module in Python to print out the process ID
    # assigned to the call of this function assigned by the operating
    # system.
    proc_id = os.getpid()
    print(f"Process ID: {proc_id}")

    # We can also use the "current_process" function to get the name
    # of the Process object:
    process_name = current_process().name
    print(f"Process Name: {process_name}")

    print(f"The number {number} squares to {result}.")


if __name__ == '__main__':

    # The processes list will store each call we make to "square" and the
    # numbers list contains the numbers we loop through and call the
    # "square" function on."
    processes = []
    numbers = [1, 2, 3, 4, 5]

    # Loop through the list of numbers, call the "square" function,
    # and store and start each call to "square".
    for i, number in enumerate(numbers):
        process = Process(target=square, args=(number,))
        processes.append(process)

        # Processes are spawned by creating a Process object and
        # then calling its start() method.
        process.start()

        if number == 2:
            process.terminate()
            time.sleep(0.01)
            print(process.is_alive())


        #print(process.is_alive())

那么会发生什么呢?我只是想检查一个进程是否还在运行。我只是感到困惑，因为我正在调用terminate函数，如果我删除了time.sleep(0.01)，它将返回True，这意味着进程仍然活着！

但是当我放入time.sleep(0.01)时，它会打印出False！这意味着进程被终止了，对吗？那么，为什么这个time.sleep(0.01)是一件大事呢？我是不是漏掉了什么？关于这个我肯定有些不明白的地方。但是请随时告诉我，如果你愿意演示一个示例代码，让我更好地理解，请成为我的客人，我会很高兴的！

包含time.sleep(0.01)时的输出

False
Process ID: 1808
Process Name: Process-1
The number 1 squares to 1.
Process ID: 17180
Process Name: Process-3
The number 3 squares to 9.
Process ID: 2488
Process Name: Process-5
The number 5 squares to 25.
Process ID: 16656
Process Name: Process-4
The number 4 squares to 16.
[Finished in 1.0s]

如果被移除，那么

True
Process ID: 1808
Process Name: Process-1
The number 1 squares to 1.
Process ID: 17180
Process Name: Process-3
The number 3 squares to 9.
Process ID: 2488
Process Name: Process-5
The number 5 squares to 25.
Process ID: 16656
Process Name: Process-4
The number 4 squares to 16.
[Finished in 1.0s]

我真的被MultiProcessing迷住了。谢谢!

Answer 1

进程本质上是在告诉python使用自己的内存和所有东西来运行一个新的python实例。这意味着每个进程都有一个启动和关闭步骤，这不是微不足道的。当您立即终止并检查时，没有足够的时间让进程实际自行终止。所需的确切时间将取决于您的平台。这是多处理的一个重要部分，多处理并不总是能节省时间。每个子进程的开销仍然需要由主线程来处理。