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Path: utzoo!watmath!clyde!cbosgd!ihnp4!godot!massar
From: massar@godot.UUCP (J.P. Massar)
Newsgroups: net.emacs
Subject: CCA Emacs Redisplay Bug Fix
Message-ID: <1076@godot.UUCP>
Date: Tue, 26-Feb-85 16:08:27 EST
Article-I.D.: godot.1076
Posted: Tue Feb 26 16:08:27 1985
Date-Received: Thu, 28-Feb-85 20:14:01 EST
Distribution: net
Organization: Thinking Machines, Cambridge, MA
Lines: 174

At times, especially when the load average is high, and especially
when you have the Time Display option set, Emacs would screw up
redisplaying the screen after processing a lot of typed characters.

For instance, if you typed 'abcdefghij' quickly

Emacs might print 'abc'

then pause and process the rest of the characters you typed without displaying 
them, then display the rest of the line which might look like

abcefghj

i.e., some characters might be 'missing'.  ('missing' because by typing
C-L the proper line

abcdefghij

will be displayed).

The problem is basically that during the times Emacs processes input 
without displaying it, it can get confused as to where the cursor really is.

Here is an essentially simple fix which solves the problem with respect
to Time Display.  Included in this is a fix which makes Emacs only check for
mail once a minute (as opposed to what it does now, which is to check
every time you type a character! (this checking does a 'stat' system
call, which presumably generates a signficant amount of I/O and 
processing)).

The fix is entirely within e_main.c.  I cannot provide diffs because of
other changes I have made.  Instead, I provide source for the two
routines that need changing:  edit and timed.
        
My first impressions are that with these fixes Emacs handles much better
under heavy loads.  

These fixes do not solve the problem entirely.  There are undoubtably
other places in the code where Emacs does similar things and likewise
gets confused about where the cursor is.  One of these may be when it
does Auto Save's.  Basically any time Emacs displays something in the
mode line or in the Echo area there is the possibly that this bug
could be present, although it is not necessarily present.

Now that the bug is understood, if anyone can produce it in circumstances
other than time redisplay it can probably be tracked down and fixed.
I don't promise to fix these cases, but I'd be interested in hearing
about the cases where it still happens.

***************************************************************************

/***** Replace the code for edit in e_main with the following *****/

***************************************************************************


#define DELTA_DT 5                      /* seconds between time redisplays */
#define DELTA_MCHECK 60                 /* seconds between mail checks */

static long clock,mailctime,dtctime;


/* EMACS main editing loop */

edit(earg)
{
	register i;
	char retval;

	for (;;) {
		if (mlhexf && !infile && (i = binsrch("Main Loop Hook", (char *)comtab, NCOMS, sizeof(struct key))) >= 0 && i < NCOMS) {
			xcnum = i;
			(void)(*comtab[i].func)(1, -1, 0, 0, 0);
		}
		disp = echocom = flushed = longline = numarg = piperr = quitf = signonly = autargf = 0;
		if (Savemd && ++nschar >= Saveint)
			asave();
		updis();
		if (bgspellf && !access(sptemp, 0)) {
			echo2("Background Spell has finished.");
			rdisputc(Ctrl('G'));
			fflush(stdout);
			sleep(1);
			goback();
			bgspellf = 0;
		}
                
                time(&clock);

#if	vms
		ckmsgs();		/* Check for broadcast messages */
#endif

#if	!vms

                /* check for mail every so often if not processing typeahead */
                
		if (Mailnote && clock > mailctime + DELTA_MCHECK && empty(0)) {
                        mailctime = clock;
			ckmail(1, 0);
                }
#endif

                /* redisplay the time if we're not processing typeahead */
                /* and some number of seconds have passed */

		if (Timemd && clock > dtctime + DELTA_DT && empty(0)) {
                        dtctime = clock;
			dtime(); 
                }
                        
#if	BSD42
		if (streqn(TERM, "sun", 3) && empty(0) && !findloc(curline, curcol))
			cc = blincur();
		else
#endif
			cc = getchar();
		if (prtermf) {
			prtermf = 0;
			continue;	/* Dummy character */
		}
		if (krappf)
			krappf--;
		if (vcolflg)
			vcolflg--;
		if (Autargm && (isdigit(cc) || cc == '-')) {
			autargf = 1;
			retval = autoarg();
		} else {
			if (Abbrevmd && (index(Abbexpch, cc) || *Addabbex && index(Addabbex, cc)))
				expabb();
			retval = keyex(1);
		}
		Sedit++;
		if (!earg || exitf || quitf && infile && !recovery)
			return(retval);
	}
}


***************************************************************************

/***** Replace the code for edit in e_main with the following *****/

***************************************************************************

/* Display the time in the lower right hand corner of the screen */

dtime()
{
	register char *tp;
	register len;
	char dtimebuf[SBUFSIZ];
	int x;
	int y;
	
		tp = ctime(&clock);
		tp[16] = 0;
		x = mapline;
		y = mapcol;
		if (*echo2buf && *echo2buf != ' ') {
			sprintf(dtimebuf, "                                                        %s", tp);
			len = min(strlen(echo2buf), 56);
			(void) strcpy(echo2buf + len, dtimebuf + len);
			echo2(echo2buf);
		} else
			echo2("                                                        %s", tp);
		newpos(x, y);
}

-- 
-- JP Massar, Thinking Machines Corporation, Cambridge, MA
-- ihnp4!godot!massar
-- massar@cca-unix