/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2026.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* svsem_demo.c

   A simple demonstration of System V semaphores.
*/
#include <sys/types.h>
#include <sys/sem.h>
#include <sys/stat.h>
#include "curr_time.h"                  /* Declaration of currTime() */
#include "semun.h"                      /* Definition of semun union */
#include "tlpi_hdr.h"

int
main(int argc, char *argv[])
{
    int semid;

    if (argc < 2 || argc > 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s init-value\n"
                 "   or: %s semid operation\n", argv[0], argv[0]);

    if (argc == 2) {            /* Create and initialize semaphore */
        union semun arg;

        semid = semget(IPC_PRIVATE, 1, S_IRUSR | S_IWUSR);
        if (semid == -1)
            errExit("semid");

        arg.val = getInt(argv[1], 0, "init-value");
        if (semctl(semid, /* semnum= */ 0, SETVAL, arg) == -1)
            errExit("semctl");

        printf("Semaphore ID = %d\n", semid);

    } else {                    /* Perform an operation on first semaphore */

        struct sembuf sop;              /* Structure defining operation */

        semid = getInt(argv[1], 0, "semid");

        sop.sem_num = 0;                /* Specifies first semaphore in set */
        sop.sem_op = getInt(argv[2], 0, "operation");
                                        /* Add, subtract, or wait for 0 */
        sop.sem_flg = 0;                /* No special options for operation */

        printf("%ld: about to semop at  %s\n", (long) getpid(), currTime("%T"));
        if (semop(semid, &sop, 1) == -1)
            errExit("semop");

        printf("%ld: semop completed at %s\n", (long) getpid(), currTime("%T"));
    }

    exit(EXIT_SUCCESS);
}