Guido van Rossum added the comment:
I revived my ancient PowerBook G4 just to get to the bottom of this.
The long and short of the issue seems to be that when subprocess.Popen() closes
the *read* end of the stdin pipe, fstat() on the *write* end starts failing
with EBADF. The exact line where the transition happens is this (aroun
subprocess.py#1375):
if p2cread != -1 and p2cwrite != -1 and p2cread != devnull_fd:
os.close(p2cread)
This is clearly a platform bug. I also verified that the child process is still
running.
Now I can't reproduce this *without* a fork+exec in the middle, so it may be
that there's something magical that's done by the _posixsubprocess.fork_exec()
call affecting the pipe, but before the above os.close() call the fstat() call
definitely reports success, so the "closing" must be happening as a side effect
of closing the other end. I'm sure there's someone at Apple with the kernel
source code who can explain this, but I think we've done our due diligence.
That switching to a socketpair fixed the issue suggests that the kernel bug is
related to pipes specifically.
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<http://bugs.python.org/issue19294>
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