python 如果 stdout=PIPE，我如何找出 subprocess.Popen wait() 为什么会永远等待？
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How can I find out why subprocess.Popen wait() waits forever if stdout=PIPE?
提问by Graeme Perrow
I have a program that writes to stdout and possibly stderr. I want to run it from python, capturing the stdout and stderr. My code looks like:
我有一个写入标准输出和可能的标准错误的程序。我想从 python 运行它，捕获标准输出和标准错误。我的代码看起来像：
from subprocess import *
p = Popen( exe, shell=TRUE, stdout=PIPE, stderr=PIPE )
rtrncode = p.wait()
For a couple of programs, this works fine, but when I added a new one, the new one hangs forever. If I remove stdout=PIPE, the program writes its output to the console and finishes and everything is fine. How can I determine what's causing the hang?
对于几个程序，这很好用，但是当我添加一个新程序时，新程序永远挂起。如果我删除stdout=PIPE，程序会将其输出写入控制台并完成，一切都很好。如何确定导致挂起的原因？
Using python 2.5 on Windows XP. The program does not read from stdin nor does it have any kind of user input (i.e. "hit a key").
在 Windows XP 上使用 python 2.5。该程序不从标准输入读取，也不具有任何类型的用户输入（即“击键”）。
回答by Alex Martelli
When a pipe's buffer fills up (typically 4KB or so), the writing process stops until a reading process has read some of the data in question; but here you're reading nothing until the subprocess is done, hence the deadlock. The docson waitput it very clearly indeed:
当管道的缓冲区填满时（通常为 4KB 左右），写入过程将停止，直到读取过程读取了一些相关数据；但是在这里，在子流程完成之前，您什么也读不到，因此陷入僵局。 该文档上wait说得非常清楚确实是：
WarningThis will deadlock if the child process generates enough output to a stdout or stderr pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use communicate() to avoid that.
警告如果子进程向 stdout 或 stderr 管道生成足够的输出，从而阻止等待 OS 管道缓冲区接受更多数据，这将导致死锁。使用communication() 来避免这种情况。
If you can't use communicatefor some reason, have the subprocess write to a temporary file, and then you can waitand read that file when it's ready -- writing to a file, instead of to a pipe, does not risk deadlock.
如果communicate由于某种原因不能使用，让子进程写入一个临时文件，然后你可以wait在它准备好时读取该文件——写入文件而不是管道，不会有死锁的风险。
回答by MitMaro
Take a look at the docs. It states that you shouldn't use wait as it can cause a dead lock. Try using communicate.
