kqueue.c

/**
 * Written by Austin Walters 5/13/2014
 * For I/O Multiplexing example on austingwalters.com
 */

#include <sys/event.h>
#include <sys/time.h> 
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h> 

/**
 * Given the file descriptor this function,
 * writes A, waits 2 second, writes "c,"
 */
void child_one_func(int fd){

  write(fd, "A - 1", 5);
  sleep(2);
  write(fd, "C - 3", 5);
  close(fd);
}

/**
 * Given the file descriptor this function,
 * Waits 1 second, writes "B", Waits 2 seconds,
 * then writes "D"
 */
void child_two_func(int fd){

  sleep(1);
  write(fd, "B - 2", 5);
  sleep(2);
  write(fd, "D - 4", 5);
  close(fd);
}

int main(){

  int kq = kqueue();
  
  /* Double-array of fds for the pipe() */
  int **fds = malloc(2 * sizeof(int *));
  struct kevent *evlist = malloc(sizeof(struct kevent));
  struct kevent *chlist = malloc(sizeof(struct kevent) * 2);

  int i;
  for (i = 0; i < 2; i++){

    /* Create a pipe */
    fds[i] = malloc(2 * sizeof(int));
    pipe(fds[i]);

    int read_fd = fds[i][0];
    int write_fd = fds[i][1];
    
    /* Generates a new process */
    pid_t pid = fork();

    /* child */
    if (pid == 0){

      close(read_fd);

      if (i == 0) { child_one_func(write_fd); }
      else if (i == 1) { child_two_func(write_fd); }

      /* Closes child */
      exit(0);

    }else{
      close(write_fd);
    }

    /* Set listener to read */
    EV_SET(&chlist[i], read_fd, EVFILT_READ, EV_ADD, 0, 0, NULL);
  }

  char str[10];
  while(1){
    /* Grab any events */
    kevent(kq, chlist, 1, evlist, 1, NULL);
    for(i = 0; i < 2; i++){
      ssize_t bytes = read(chlist[i].ident, &str, 10);
      if(bytes > 0)
	printf("Read: %s\n", str);
      
      if(strcmp(str, "D - 4") == 0)
	return 0;
    }
  }
  free(chlist);
  free(evlist);
  close(kq);
  return 0;
}