#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

/*  sem_add.c  - a program that adds a value to a semaphore  **/

/*  usage: sem_add key semnum amount
 * action: program creates a semaphore with key `key', sets its initial
 *	   value to zero then blocks waiting to decrement it
 */

#define oops(m,x) { perror(m); exit(x); }
union semun { int val; struct semid_ds *buf; ushort *array; };

main(int ac, char *av[])
{
	int	     semid;		/* an id		*/
	union semun  sem_info;		/* some properties	*/
	struct sembuf action;		/* action for the sem   */
	int	     increment;
	int	     keynum ;
	int	     semnum;

	if ( ac != 4 ){
		printf("usage: sem_block key semnum amt\n"); exit(1);
	}
	increment = atoi(av[3]);
	semnum    = atoi(av[2]);
	keynum    = atoi(av[1]);

	/*
	 * connect to a semset with 1 semaphore in it
	 */

	semid = semget( keynum, semnum+1, 0 );
	if( semid == -1 )
		oops("semget",2);

	/*
	 * prepare the increment command
	 */

	action.sem_num = semnum;	/* action for semaphore */
	action.sem_flg = SEM_UNDO;	/* auto clean up	  */
	
	action.sem_op  = increment;	/* INCREMENT SEMAPHORE */

	/*
	 * about to increment semaphore 0 in the set....
	 */

	printf("sem_add about to add %d to semaphore\n", increment);
	semop( semid, &action, 1);	/* only one action */
	printf("sem_add DONE!\n");
	sleep(3);
}