This is signals/sig_speed_sigsuspend.c, an example to accompany the book, The Linux Programming Interface.

This file is not printed in the book; it is a supplementary file for Chapter 22.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.


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Function list (Bold in this list means a function is not static)

/* 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

   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)

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;
    sa.sa_flags = 0;
    sa.sa_handler = handler;
    if (sigaction(TESTSIG, &sa, NULL) == -1)

    /* 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;
    sigaddset(&blockedMask, TESTSIG);
    if (sigprocmask(SIG_SETMASK, &blockedMask, NULL) == -1)


    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)
            if (sigsuspend(&emptyMask) == -1 && errno != EINTR)

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


Download signals/sig_speed_sigsuspend.c

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