signals/sigmask_longjmp.c

This is signals/sigmask_longjmp.c (Listing 21-2, page 432), an example from the book, The Linux Programming Interface.

The source code file is copyright 2010, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* sigmask_longjmp.c

   Demonstrate the different effects of longjmp() and siglongjmp()
   on the process signal mask.

   By default, this program uses setjmp() + longjmp(). Compile with
   -DUSE_SIGSETJMP to use sigsetjmp() + siglongjmp().
*/
#define _GNU_SOURCE     /* Get strsignal() declaration from <string.h> */
#include <string.h>
#include <setjmp.h>
#include <signal.h>
#include "signal_functions.h"           /* Declaration of printSigMask() */
#include "tlpi_hdr.h"

static volatile sig_atomic_t canJump = 0;
                        /* Set to 1 once "env" buffer has been
                           initialized by [sig]setjmp() */
#ifdef USE_SIGSETJMP
static sigjmp_buf senv;
#else
static jmp_buf env;
#endif
static void
handler(int sig)
{
    /* UNSAFE: This handler uses non-async-signal-safe functions
       (printf(), strsignal(), printSigMask(); see Section 21.1.2) */

    printf("Received signal %d (%s), signal mask is:\n", sig,
            strsignal(sig));
    printSigMask(stdout, NULL);

    if (!canJump) {
        printf("'env' buffer not yet set, doing a simple return\n");
        return;
    }

#ifdef USE_SIGSETJMP
    siglongjmp(senv, 1);
#else
    longjmp(env, 1);
#endif
}
int
main(int argc, char *argv[])
{
    struct sigaction sa;

    printSigMask(stdout, "Signal mask at startup:\n");

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sa.sa_handler = handler;
    if (sigaction(SIGINT, &sa, NULL) == -1)
        errExit("sigaction");

#ifdef USE_SIGSETJMP
    printf("Calling sigsetjmp()\n");
    if (sigsetjmp(senv, 1) == 0)
#else
    printf("Calling setjmp()\n");
    if (setjmp(env) == 0)
#endif
        canJump = 1;                    /* Executed after [sig]setjmp() */

    else                                /* Executed after [sig]longjmp() */
        printSigMask(stdout, "After jump from handler, signal mask is:\n" );

    for (;;)                            /* Wait for signals until killed */
        pause();
}

 

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