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

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

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

/*  srand( time( NULL ) ); */

  for ( i = 0 ; i < children ; i++ )
  {
    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( time( NULL ) ); */
  srand( time( NULL ) * getpid() * getpid() );
  t = 10 + ( rand() % 21 );  /* [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 */
  pid_t child_pid;

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

  while ( children > 0 )
  {
    /* wait until a child process exits */
    child_pid = wait( &status );   /* BLOCKS */

    children--;

    printf( "PARENT: child process %d exited...", child_pid );

    if ( WIFSIGNALED( status ) )   /* e.g. core dump */
    {
      printf( "...abnormally\n" );
    }
    else if ( WIFEXITED( status ) )
    {
      int rc = WEXITSTATUS( status );
      printf( "...after sleeping %d seconds\n", rc );
    }

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

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