example/posix/processes-signals.c

Shows process forking and signalling

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>

// A function that gets called if it is
// installed as a handler for a signal and
// that signal is recieved by the process
void handle_signal(int signum)
{
    const char* signame = "UNKNOWN";
    if(signum == SIGTERM) signame = "TERM";
    if(signum == SIGCHLD) signame = "CHLD";

    printf("Process %d received signal '%s'\n", getpid(), signame);
}

int main(int argc, const char* argv[])
{
    srand(getpid());

    printf("Main process %d started\n", getpid());

    // install the sighandler
    signal(SIGTERM, handle_signal);
    signal(SIGCHLD, handle_signal);

    // try to fork the process
    pid_t fork_result = fork();

    // if that failed
    if(fork_result < 0)
    {
        // complain and exit
        perror("Fork failed");
        return fork_result;
    }

    // if we are here and fork_result is 0 then we are
    // in the child process
    if(fork_result == 0)
    {
        // pretend doing some "work"
        sleep(3);
        return 0;
    }
    // otherwise this is executing in the parent process
    else
    {
        // wait for a while
        sleep(1);
        // and then send the TERM signal to the child
        if(rand() % 2 == 0)
            kill(fork_result, SIGTERM);
        else kill(fork_result, SIGINT);

        int status = 0;
        wait(&status);

        // if the process exitted normally
        if(WIFEXITED(status))
            printf("Child %d exitted with code %d\n", fork_result, WEXITSTATUS(status));

        // if the process was terminated by a signal
        if(WIFSIGNALED(status))
            printf("Child %d terminated by signal %d\n", fork_result, WTERMSIG(status));
    }
    return 0;
}