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From: Edward Lam <triplequadsupport@gmail.com>
Date: Thu, 30 Jan 2020 14:03:50 -0500
Message-ID: <CAJZe6MDdZnE7BNZQWSHgaLo6sbx+9KVhG+wKfcruh_exPaZFLQ@mail.gmail.com>
Subject: Pipes bug when spawning non-cygwin processes
To: cygwin@cygwin.com
Content-Type: text/plain; charset="UTF-8"

Hi Folks,

I'm getting a problem where cygwin parent processes spawning non-cygwin
child processes no longer detect when stdin has been closed. Please see the
sample python code at the end where I've isolated the problem. I've got
cygwin's python2 running spawn_bar.py that popen's a native non-cygwin
python2 running bar.py. The steps to reproduce are to run this command
using the two files detailed at the end of this email:

$ python2 spawn_bar.py

On Windows 10, this command quits right away as expected when using cygwin
3.0.7 but hangs when using cygwin 3.1.2 (version number as reported from
running `cygcheck -c cygwin`).

Looking through the release logs, nothing sticks out except for the change
in 3.1.0 that mentions PTY changes. However, when I originally ran into
this, it wasn't even being done through a terminal but some background
script.

Any ideas?

Thanks,
-Edward

# spawn_bar.py
import os
import subprocess
import sys
python = "python2" # this works
python = "/path/to/native/python2" # this hangs
p = subprocess.Popen([python, 'bar.py'], stdin=subprocess.PIPE)
p.stdin.close()
pid, status = os.waitpid(p.pid, 0)

# bar.py
import sys
for line in sys.stdin:
    print 'got: ' + line

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