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"^D^H^H" in process output on Darwin (Was Re: grep-use-null-device)

From: YAMAMOTO Mitsuharu
Subject: "^D^H^H" in process output on Darwin (Was Re: grep-use-null-device)
Date: Sat, 27 Aug 2005 10:30:41 +0900
User-agent: Wanderlust/2.14.0 (Africa) SEMI/1.14.6 (Maruoka) FLIM/1.14.6 (Marutamachi) APEL/10.6 Emacs/22.0.50 (sparc-sun-solaris2.8) MULE/5.0 (SAKAKI)

>>>>> On Sat, 20 Aug 2005 15:22:41 +0300, Eli Zaretskii <address@hidden> said:

>> Thanks for posting the URL, though it seems that the web interface
>> at lists.gnu.org eats multiple spaces.  Here is the Gmane URL for
>> the original post from Kevin Rodgers with correct indentation:
>> http://article.gmane.org/gmane.emacs.devel/33146
>> Can someone please install it?

> Done.

With this change, we sometimes see "^D^H^H" at the head of the output
of grep on Darwin/Mac OS X with whichever window systems (^H is
actually in one character).  It looks as if the tty echo option is not
disabled and ^D is echoed back in response to process-send-eof.

I think this is because Emacs may send some data before a subprocess
completes tty options setup.  On Darwin, vfork is defined as fork for
the reason mentioned in src/s/darwin.h.

/* The following solves the problem that Emacs hangs when evaluating
   (make-comint "test0" "/nodir/nofile" nil "") when /nodir/nofile
   does not exist.  */
#define vfork fork

(It actually hangs on Mac OS X 10.1.5 and 10.2.8 if
process-connection-type is set to t.  On Mac OS X 10.3.9 it seems not
to hang.  Are there any other problems with vfork on Mac OS X 10.3,
which is based on Darwin 7?)

Unlike vfork, the parent process may run before the child process
executes the code between (v)fork and execve/_exit if fork is used.
The current Emacs disables the tty echo option in the child process
(for USG systems?) by calling child_setup_tty.

The following patch does tty options setup before forking, and it
works for me.

                                     YAMAMOTO Mitsuharu

Index: src/process.c
RCS file: /cvsroot/emacs/emacs/src/process.c,v
retrieving revision 1.463
diff -c -r1.463 process.c
*** src/process.c       15 Aug 2005 08:44:53 -0000      1.463
--- src/process.c       27 Aug 2005 01:25:30 -0000
*** 1793,1798 ****
--- 1793,1802 ----
        if (forkin < 0)
        report_file_error ("Opening pty", Qnil);
+       /* In the case that vfork is defined as fork, the parent process
+        (Emacs) may send some data before the child process completes
+        tty options setup.  So we setup tty before forking.  */
+       child_setup_tty (forkout);
        forkin = forkout = -1;
  #endif /* not USG, or USG_SUBTTY_WORKS */

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