Python、Popen 和 select - 等待进程终止或超时 [英] Python, Popen and select - waiting for a process to terminate or a timeout

问题描述

我使用以下方法运行子进程:

I run a subprocess using:

  p = subprocess.Popen("subprocess", 
                       stdout=subprocess.PIPE, 
                       stderr=subprocess.PIPE, 
                       stdin=subprocess.PIPE)

这个子进程可能会立即退出并在 stderr 上出现错误，或者继续运行.我想检测这两种情况中的任何一种 - 后者需要等待几秒钟.

This subprocess could either exit immediately with an error on stderr, or keep running. I want to detect either of these conditions - the latter by waiting for several seconds.

我试过了:

  SECONDS_TO_WAIT = 10
  select.select([], 
                [p.stdout, p.stderr], 
                [p.stdout, p.stderr],
                SECONDS_TO_WAIT)

但它只是返回:

  ([],[],[])

在任一条件下.我能做什么?

on either condition. What can I do?

推荐答案

您是否尝试过使用 Popen.Poll() 方法.你可以这样做:

Have you tried using the Popen.Poll() method. You could just do this:

p = subprocess.Popen("subprocess", 
                   stdout=subprocess.PIPE, 
                   stderr=subprocess.PIPE, 
                   stdin=subprocess.PIPE)

time.sleep(SECONDS_TO_WAIT)
retcode = p.poll()
if retcode is not None:
   # process has terminated

这将导致您总是等待 10 秒，但如果失败案例很少见，这将在所有成功案例中摊销.

This will cause you to always wait 10 seconds, but if the failure case is rare this would be amortized over all the success cases.

怎么样:

t_nought = time.time()
seconds_passed = 0

while(p.poll() is not None and seconds_passed < 10):
    seconds_passed = time.time() - t_nought

if seconds_passed >= 10:
   #TIMED OUT

这有一种忙碌等待的丑陋，但我认为它完成了你想要的.

This has the ugliness of being a busy wait, but I think it accomplishes what you want.

另外再看一遍 select 调用文档，我想你可能想把它改成如下:

Additionally looking at the select call documentation again I think you may want to change it as follows:

SECONDS_TO_WAIT = 10
  select.select([p.stderr], 
                [], 
                [p.stdout, p.stderr],
                SECONDS_TO_WAIT)

由于您通常希望从 stderr 中读取数据，因此您想知道它何时可以读取某些内容(即失败情况).

Since you would typically want to read from stderr, you want to know when it has something available to read (ie the failure case).

我希望这会有所帮助.

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