PATCH: 3.1.5-pws-17: typeahead de-kludge

[Peter Stephenson <pws@xxxxxxxxxxxxxxxxx>]

This is an attempt to remove flakiness permanently from zsh typeahead.
Some machines mess up typeahead when you go from canonical to non-canonical
input processing; programmes are usually called with the former in effect,
while zle works with the latter.  The old code caused the terminal mode not
to be changed if there was typeahead, but only on the machines where we
knew there was a problem:  that's because it was possible to get into a
state where zle didn't work because the terminal hadn't been set up
for input properly (I've seen this, but haven't worked out how to reproduce
it systematically).

The test for typeahead actually tells you how many characters there are to
read.  So this patch implements something if anything even more obvious
than the existing code: it actually reads those characters and stores them
in the unget queue, then sets the terminal up unconditionally so all future
input will work.

I think it's now possible to use this code for all systems, whether there
was a typeahead problem or not.  The reasoning is
- Where there was no problem, we just get stuff in the unget buffer instead
of straight from read(), so there is nothing extra to go wrong.
- Where there was a problem, it had to perform this test each time it
wanted to set up the terminal anyway.  So it should introduce no new
problems.  In particular, the potential race condition between the ioctl()
test and setting the terminal is hardly worse (just the extra four lines).
If anyone's worried, it can be changed to loop over the ioctl() until val
returns 0, and then it is exactly the same as before.  But in that case
problably the thing to do would be to delay the test until just before the
final settyinfo().

The only possible troubles I can see are (i) I've got confused over
ordering of stuff in the unget buffer so typeahead appears in the wrong
place (i.e. possibly I should have made sure the new input goes at the
front of the unget buffer and not at the end, since it's LIFO).  However, I
don't think zsetterm() gets called when this is likely to be a problem.
Note the internal unget mechanism is entirely separate from the buffer
stack.

(ii) Some bright spark may have designed an OS where rational
considerations of this kind don't apply.  I've tested it on AIX 3.2, HPUX
10.20 and IRIX 6.2 and there's no sign of a problem, however (all define
FIONREAD, which SunOS 5 appears not to unless in some BSD compatibility
mode).  Apart from that, this looks a candidate for putting in 3.0.6.


--- Src/Zle/zle_main.c.ta	Mon May  3 16:24:11 1999
+++ Src/Zle/zle_main.c	Mon May  3 16:37:39 1999
@@ -119,12 +119,16 @@
 {
     struct ttyinfo ti;
 
-#if defined(CLOBBERS_TYPEAHEAD) && defined(FIONREAD)
+#if defined(FIONREAD)
     int val;
 
     ioctl(SHTTY, FIONREAD, (char *)&val);
-    if (val)
-	return;
+    if (val) {
+	char *tmpline = (char *)zalloc(val);
+	read(SHTTY, tmpline, val);
+	ungetkeys(tmpline, val);
+	zfree(tmpline, val);
+    }
 #endif
 
 /* sanitize the tty */
--- acconfig.h.ta	Thu Mar 11 11:20:39 1999
+++ acconfig.h	Mon May  3 16:38:25 1999
@@ -189,9 +189,6 @@
 /* Define to 1 if struct timezone is defined by a system header */
 #undef HAVE_STRUCT_TIMEZONE
 
-/* Define if your system's typeahead disappears from the shell editor. */
-#undef CLOBBERS_TYPEAHEAD
-
 /* Define to 1 if there is a prototype defined for brk() on your system */
 #undef HAVE_BRK_PROTO
 
--- configure.in.ta	Mon Mar 15 12:11:29 1999
+++ configure.in	Mon May  3 16:38:10 1999
@@ -883,25 +883,6 @@
 zsh_PATH_UTMP(utmpx)
 zsh_PATH_UTMP(wtmpx)
 
-dnl ----------------
-dnl TYPEAHEAD KLUDGE
-dnl ----------------
-dnl Some systems clobber typeahead when you go from canonical input
-dnl processing to non-canonical, so we need a FIONREAD ioctl.
-dnl I don't know how to check this with configure, so I am using the
-dnl system names directly.
-dnl The doubled square brackets are necessary because autoconf uses m4.
-AC_CACHE_CHECK(if typeahead needs FIONREAD, zsh_cv_sys_clobbers_typeahead,
-[case x-$host_vendor-$host_os in
-    x-*-ultrix* | x-*-dgux* | x-sni-sysv4* | x-*-irix*)
-	zsh_cv_sys_clobbers_typeahead=yes;;
-    *)
-	zsh_cv_sys_clobbers_typeahead=no;;
-esac])
-if test $zsh_cv_sys_clobbers_typeahead = yes; then
-  AC_DEFINE(CLOBBERS_TYPEAHEAD)
-fi
-
 dnl -------------------
 dnl brk/sbrk PROTOTYPES
 dnl -------------------

-- 
Peter Stephenson <pws@xxxxxxxxxxxxxxxxx>       Tel: +39 050 844536
WWW:  http://www.ifh.de/~pws/
Dipartimento di Fisica, Via Buonarroti 2, 56127 Pisa, Italy