signals/sig_speed_sigsuspend.c

/* sig_speed_sigsuspend.c

   This program times how fast signals are sent and received.

   The program forks to create a parent and a child process that alternately
   send signals to each other (the child starts first). Each process catches
   the signal with a handler, and waits for signals to arrive using
   sigsuspend().

   Usage: $ time ./sig_speed_sigsuspend num-sigs

   The 'num-sigs' argument specifies how many times the parent and
   child send signals to each other.

   Child                                  Parent

   for (s = 0; s < numSigs; s++) {        for (s = 0; s < numSigs; s++) {
       send signal to parent                  wait for signal from child
       wait for a signal from parent          send a signal to child
   }                                      }
*/
#include <signal.h>
#include "tlpi_hdr.h"

static void
handler(int sig)
{
}

#define TESTSIG SIGUSR1

int
main(int argc, char *argv[])
{
    if (argc != 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s num-sigs\n", argv[0]);

    int numSigs = getInt(argv[1], GN_GT_0, "num-sigs");

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

    /* Block the signal before fork(), so that the child doesn't manage
       to send it to the parent before the parent is ready to catch it */

    sigset_t blockedMask, emptyMask;
    sigemptyset(&blockedMask);
    sigaddset(&blockedMask, TESTSIG);
    if (sigprocmask(SIG_SETMASK, &blockedMask, NULL) == -1)
        errExit("sigprocmask");

    sigemptyset(&emptyMask);

    pid_t childPid = fork();
    switch (childPid) {
    case -1: errExit("fork");

    case 0:     /* child */
        for (int scnt = 0; scnt < numSigs; scnt++) {
            if (kill(getppid(), TESTSIG) == -1)
                errExit("kill");
            if (sigsuspend(&emptyMask) == -1 && errno != EINTR)
                    errExit("sigsuspend");
        }
        exit(EXIT_SUCCESS);

    default: /* parent */
        for (int scnt = 0; scnt < numSigs; scnt++) {
            if (sigsuspend(&emptyMask) == -1 && errno != EINTR)
                    errExit("sigsuspend");
            if (kill(childPid, TESTSIG) == -1)
                errExit("kill");
        }
        exit(EXIT_SUCCESS);
    }
}