timers/ptmr_sigev_signal.c

/* ptmr_sigev_signal.c

   This program demonstrates the use of signals as the notification mechanism
   for expirations of a POSIX timer. Each of the program's command-line
   arguments specifies the initial value and interval for a POSIX timer. The
   format of these arguments is defined by the function itimerspecFromStr().

   The program establishes a handler for the timer notification signal, creates
   and arms one timer for each command-line argument, and then pauses. Each
   timer expiration causes the generation of a signal, and, when invoked, the
   signal handler displays information about the timer expiration.

   Kernel support for Linux timers is provided since Linux 2.6. On older
   systems, an incomplete user-space implementation of POSIX timers
   was provided in glibc.
*/
#define _POSIX_C_SOURCE 199309
#include <signal.h>
#include <time.h>
#include "curr_time.h"                  /* Declares currTime() */
#include "itimerspec_from_str.h"        /* Declares itimerspecFromStr() */
#include "tlpi_hdr.h"

#define TIMER_SIG SIGRTMAX              /* Our timer notification signal */

static void
handler(int sig, siginfo_t *si, void *uc)
{
    timer_t *tidptr;

    tidptr = si->si_value.sival_ptr;

    /* UNSAFE: This handler uses non-async-signal-safe functions
       (printf(); see Section 21.1.2) */

    printf("[%s] Got signal %d\n", currTime("%T"), sig);
    printf("    *sival_ptr         = %ld\n", (long) *tidptr);
    printf("    timer_getoverrun() = %d\n", timer_getoverrun(*tidptr));
}

int
main(int argc, char *argv[])
{
    struct itimerspec ts;
    struct sigaction  sa;
    struct sigevent   sev;
    timer_t *tidlist;
    int j;

    if (argc < 2)
        usageErr("%s secs[/nsecs][:int-secs[/int-nsecs]]...\n", argv[0]);

    tidlist = calloc(argc - 1, sizeof(timer_t));
    if (tidlist == NULL)
        errExit("malloc");

    /* Establish handler for notification signal */

    sa.sa_flags = SA_SIGINFO;
    sa.sa_sigaction = handler;
    sigemptyset(&sa.sa_mask);
    if (sigaction(TIMER_SIG, &sa, NULL) == -1)
        errExit("sigaction");

    /* Create and start one timer for each command-line argument */

    sev.sigev_notify = SIGEV_SIGNAL;    /* Notify via signal */
    sev.sigev_signo = TIMER_SIG;        /* Notify using this signal */

    for (j = 0; j < argc - 1; j++) {
        itimerspecFromStr(argv[j + 1], &ts);

        sev.sigev_value.sival_ptr = &tidlist[j];
                /* Allows handler to get ID of this timer */

        if (timer_create(CLOCK_REALTIME, &sev, &tidlist[j]) == -1)
            errExit("timer_create");
        printf("Timer ID: %ld (%s)\n", (long) tidlist[j], argv[j + 1]);

        if (timer_settime(tidlist[j], 0, &ts, NULL) == -1)
            errExit("timer_settime");
    }

    for (;;)                            /* Wait for incoming timer signals */
        pause();
}