Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!rochester!udel!mmdf
From: iphwk%MTSUNIX1.BITNET@cunyvm.cuny.edu (Bill Kinnersley)
Newsgroups: comp.sys.amiga
Subject: Sample Exception Handler
Message-ID: <3447@louie.udel.EDU>
Date: 24 Jul 88 03:41:45 GMT
Sender: mmdf@udel.EDU
Lines: 118

Well, I guess I answered my own question out of necessity.  Here is
my attempt at writing an Exception Handler.  The program will loop
indefinitely, and catch the signals that result from typing either
^C, ^D, ^E, or ^F.  In addition, ^C will abort the program.
If people out there with experience in these matters see any mistakes
I've made, please let me know..


Bill Kinnersley
  Physics Department            BITNET: iphwk@mtsunix1
  Montana State University      INTERNET: iphwk%mtsunix1.bitnet@cunyvm.cuny.edu
  Bozeman, MT 59717             CSNET: iphwk%mtsunix1.bitnet@relay.cs.net
  (406)994-3614                 UUCP: ...psuvax1!mtsunix1.bitnet!iphwk
"He learned to communicate with birds and discovered that their conversation
was fantastically boring.  It was all to do with wind speed, wingspan,
power-to-weight ratios and a fair bit about berries."

----------------

/* An illustration of how to write an Exception Handler */
/* Bill Kinnersley - IPHWK@MTSUNIX1.BITNET - 7/23/88    */
/* Compiled using Aztec 3.4a, 16-bit integers.          */
/* ^D, ^E, ^F will print a message, ^C will abort.      */

#include <stdio.h>
#include <exec/types.h>
#include <exec/tasks.h>
#include <libraries/dos.h>
#include <functions.h>

extern short Enable_Abort;
long aborted, cursigs, mysigs, oldsigs;

struct Task *mytask;

main() {
/* Install my handler */

        install();

/* Make sure that Aztec does not catch any ^C's */

        Enable_Abort = 0;

/* Busy loop simulating something useful...             */
/* Note that each Exception DOES break into this loop.  */
/* The aborted flag is polled only because              */
/* I want to generate a clean exit from main(),         */
/* not try to call cleanup from inside the handler.     */

        while (!aborted) {}

/* It's essential to put things back the way they were  */
/* Exceptions are task-specific, but all programs run   */
/* from the same CLI will reuse the same Task structure */

        cleanup();
}

APTR oldcode;

install() {
        int face();

        mysigs = SIGBREAKF_CTRL_C | SIGBREAKF_CTRL_D |
                SIGBREAKF_CTRL_E | SIGBREAKF_CTRL_F;
        mytask = FindTask(0L);

/* Don't anyone else bother me while I'm changing my Task structure */

        Forbid();

/* Save the old Exception Handler and install my own */

        oldcode = mytask->tc_ExceptCode;
        mytask->tc_ExceptCode = (APTR)face;

/* I won't use the tc_ExceptData field...leave it unchanged */

        Permit();

/* Save the old Exception signals so we can put them back later */

        oldsigs = SetExcept(mysigs, mysigs);
}

cleanup() {
/* Restore the previous Exception Handler (ROM-wack?) */
        Forbid();
        mytask->tc_ExceptCode = oldcode;
        Permit();
        SetExcept(0L,mysigs);
}

#asm
_face:
;the signals will be passed to me in d0
        move.l  d0,-(a7)
;restore a4, which points to Aztec's small data segment */
        public  _geta4
        jsr     _geta4
        move.l  (a7)+,_cursigs

        jsr     _hdlr

;return signals to the system so they can be reset
        move.l  _cursigs,d0
        rts
#endasm

hdlr() {
/* Note that even AmigaDOS stuff can be done from here */
        printf("Exception %lx   Control-",cursigs);
        if (cursigs & SIGBREAKF_CTRL_C) {printf("C\n"); aborted=1;}
        if (cursigs & SIGBREAKF_CTRL_D) printf("D\n");
        if (cursigs & SIGBREAKF_CTRL_E) printf("E\n");
        if (cursigs & SIGBREAKF_CTRL_F) printf("F\n");
}