Re: [PATCH] Add facility to collect stderr of async subprocess

[Eli Zaretskii <eliz@gnu.org>]

> From: Daiki Ueno <ueno@gnu.org>
> Cc: emacs-devel@gnu.org
> Date: Wed, 08 Apr 2015 09:21:28 +0900
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > However, please note that the call to emacs_pipe2 in make-pipe-process
> > will hit an assertion in w32.c's implementation of pipe2.
> 
> OK, I added a wrapper around pipe2 in w32.c to preserve the assert
> condition.  With the attached patch, I confirmed that the included test
> passes on both Windows and GNU/Linux.

Thanks.

However, I think this is not the right solution.  The assertion is
there because w32.c:pipe2 calls _pipe with two flags, _O_BINARY and
_O_NOINHERIT, which exactly correspond to the flags being tested by
the assertion.  To support different combinations of flags, the flags
passed to _pipe need to be computed dynamically based on the argument
passed to pipe2.  By contrast, with your wrapper, the pipe will always
be closed in the subprocess, which I think is not what we want (does
the test actually test this aspect?), and is at least confusing when
reading the source (a.k.a. "looks like a bug").

> - Add a new function 'pipe_open' analogous to 'serial_open', which has
>   different definitions on Windows and on GNU/Linux

The sysdep.c definition of pipe_open is for all Posix platforms, I
think, not just for GNU/Linux.