在进程之间共享变量 [英] Sharing a variable between processes

问题描述

我有一个下载功能，可并行下载多个文件。
我使用 multiprocessing.Pool.map_async 为了下载不同的同一个文件的块。
我想显示一个状态栏的下载。为此，我需要知道已经下载的总字节数（ total_bytes_dl ）。

I have a downloader function that downloads multiple files parallely. I use multiprocessing.Pool.map_async in order to download different chunks of the same file. I would like to show a statusbar of the download. For this, I need to know the total bytes that has been already downloaded (total_bytes_dl).

    pool = multiprocessing.Pool(processes)
    mapObj = pool.map_async(f, args)

    while not mapObj.ready():
        status = r"%.2f MB / %.2f MB" % (total_bytes_dl / 1024.0 / 1024.0, filesize / 1024.0 / 1024.0,)
        status = status + chr(8)*(len(status)+1)
        print status,
        time.sleep(0.5)

有没有办法设置一个变量将在所有这些进程和主进程之间共享，所以每个进程都可以追加刚刚下载的字节数？

Is there a way to set a variable that will be shared among all these processes AND the main process, so every process can append the amount of bytes that has just downloaded?

推荐答案

解决方案是帮助新进程，并传递共享ctypes值：

The solution was to intilize the new process and pass the shared ctypes value:

from ctypes import c_int
import dummy

shared_bytes_var = multiprocessing.Value(c_int)

def Func(...):
    ....
    pool = multiprocessing.Pool(initializer=_initProcess,initargs=(shared_bytes_var,))
    ....

def _initProcess(x):
  dummy.shared_bytes_var = x

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