95 lines
2.5 KiB
C
95 lines
2.5 KiB
C
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/* This file is part of the sample code and exercises
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* used by the class "Advanced Programming in the UNIX
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* Environment" taught by Jan Schaumann
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* <jschauma@netmeister.org> at Stevens Institute of
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* Technology.
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*
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* This file is in the public domain.
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*
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* You don't have to, but if you feel like
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* acknowledging where you got this code, you may
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* reference me by name, email address, or point
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* people to the course website:
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* https://stevens.netmeister.org/631/
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*/
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/* This program illustrates the previously default
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* behavior or signal handlers: each invocation reset
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* the disposition to SIG_DFL.
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*
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* Hit ^\ and we jump into sig_quit_reset, which
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* resets the signal disposition to the original
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* default (which is to quit with a core dump). If
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* you hit ^\ while in sig_quit_reset, the signal is
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* queued and delivered as soon as the signal handler
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* terminates. At that point, however, the default
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* signal handler has been installed, and the program
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* exits.
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*
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* This happens whether or not you exit the signal
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* handler normally or are transferred out of by
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* another signal.
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*/
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#include <err.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#ifndef SLEEP
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#define SLEEP 5
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#endif
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int s = 0;
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static void
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sig_quit_reset(int signo) {
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if (signal(signo, SIG_DFL) == SIG_ERR) {
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err(EXIT_FAILURE, "unable to reset SIGQUIT");
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/* NOTREACHED */
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}
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(void)printf("In sig_quit_reset, s=%d. Now sleeping...\n", ++s);
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/* This call to sleep(3) can itself be
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* interrupted if we receive a signal other
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* than SIGQUIT while executing this signal
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* handler. If that happens, then we jump
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* into the other signal handler; when that
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* handler completes, we are returned back
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* here. */
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(void)sleep(SLEEP);
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(void)printf("sig_quit_reset, s=%d: exiting\n", s);
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}
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static void
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sig_int(int signo) {
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(void)signo;
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(void)printf("Now in sig_int, s=%d. Returning immediately.\n", ++s);
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}
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int
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main(void) {
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(void)printf("\n=> Establishing initial signal hander via signal(3).\n");
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if (signal(SIGINT, sig_int) == SIG_ERR) {
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err(EXIT_FAILURE, "unable to set SIGINT signal handler");
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/* NOTREACHED */
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}
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(void)printf("\n=> Establishing a resetting signal hander via signal(3).\n");
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if (signal(SIGQUIT, sig_quit_reset) == SIG_ERR) {
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err(EXIT_FAILURE, "unable to set SIGQUIT signal handler");
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/* NOTREACHED */
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}
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(void)sleep(SLEEP);
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(void)printf("\n=> Time for a second interruption.\n");
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(void)sleep(SLEEP);
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(void)printf("Now exiting.\n");
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exit(EXIT_SUCCESS);
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}
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