带有多重处理的 python 代码每次只产生一个进程 [英] python code with mulitprocessing only spawns one process each time

问题描述

我有一个简单的python代码，试图将一批jpg文件转换为png.但是这段代码每次在我的linux机器上只生成一个子进程，这段代码有什么问题?

I have a simple python code, trying to convert a batch of jpg file to png. But this code only spawn one subprocess each time on my linux machine, what's the problem with this code?

from scipy.misc import imread, imsave
from multiprocessing import Process, util
import logging

util.log_to_stderr(level=logging.DEBUG)
def imgcvt(inf, outf):
    im=imread(inf)
    imsave(outf,im)

for i in range(3):
    run_list = [];
    threads = [];
    for j in range(1,21):
        fn = str(i*20+j+1)
        run_list.append((fn+".jpg", fn+".png"))
    for dev in run_list:
        proc = Process(target=imgcvt, args=dev)
        proc.start()
        proc.join()

谢谢

推荐答案

在启动每个进程后执行 proc.join() 意味着您在继续之前等待它终止.

Doing a proc.join() after starting every process means you are waiting for it to terminate before continuing.

相反，您应该将所有 Process 对象存储到一个列表中，然后加入所有对象:

Instead, you should store all Process objects to a list, and then join on all of them:

processes = []
for dev in run_list:
    proc = Process(target=imgcvt, args=dev)
    proc.start()
    processes.append(proc)
for proc in processes:
    proc.join()

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