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

/* function prototypes */
int child();
void parent( int children );

int main()
{
 int i, children = 8;   /* based on a true story .... */

 for ( i = 0 ; i < children ; i++ )
 {
   /* fork a child process */
   pid_t z = fork();

   if ( z < 0 ) {
     fprintf( stderr, "ERROR: fork() failed.\n" );
     exit( 1 );
   }

   if ( z == 0 ) {
     int rc = child();
     exit( rc );
   }
 }

 parent( children );

 return 0;
}

int child()
{
 int t;
 printf( "CHILD: I'm new. My pid is %d.\n", getpid() );

 srand( getpid() * getpid() );
 t = 10 + ( rand() % 21 );      /* in range [10,30] */
 printf( "CHILD: I'm gonna nap for %d seconds.\n", t );
 sleep( t );
 return t;
}

void parent( int children )
{
 int status;  /* return status from a child process */
 pid_t child_pid;

 printf( "PARENT: I'm waiting for my children.\n" );

 while ( children > 0 )
 {
#if 0
   /* wait (BLOCK!) until child process exits */
   child_pid = wait( &status );
#endif

   /* see if a child has terminated -- NONBLOCKING wait */
   child_pid = waitpid( 0, &status, WNOHANG );

   if ( child_pid == 0 )
   {
     printf( "PARENT: I'm still waiting.  I'll take nap.\n" );
     sleep( 3 );
   }
   else
   {
     /* one less child to wait for ... */
     children--;

     printf( "PARENT: child process id %d exited", child_pid );
     if ( ( status & 0x000F ) != 0 ) {
       printf( " abnormally.\n" );
     } else {
       int rc = status >> 8;  /* shift right 8 bits */
       rc = rc & 0x00FF;  /* mask most-significant bytes */
       printf( " after sleeping for %d seconds.\n", rc );
     }

     printf( "PARENT: %d more to go.\n", children );
   }
 }

 printf( "PARENT: All done.\n" );
}