#include "pcsem.h"


int pcsem::init(key_t key, unsigned int value) {
    int semid, perms;
     
    perms = S_IRUSR | S_IWUSR;

    semid = semget(key, 1, IPC_CREAT | IPC_EXCL | perms);

    if (semid != -1) {                  /* Successfully created the semaphore */
        union semun arg;
        struct sembuf sop;

        fprintf(stderr, "%ld: created semaphore\n", (long) getpid());

        arg.val = 0;                    /* So initialize it to 0 */
        if (semctl(semid, 0, SETVAL, arg) == -1)
            err_exit(errno, "semctl 1");
        fprintf(stderr, "%ld: initialized semaphore\n", (long) getpid());

        /* Perform a "no-op" semaphore operation - changes sem_otime
           so other processes can see we've initialized the set. */

        sop.sem_num = 0;                /* Operate on semaphore 0 */
        sop.sem_op = value;                
        sop.sem_flg = 0;
        if (semop(semid, &sop, 1) == -1)
            err_exit(errno, "semop");
        fprintf(stderr, "%ld: completed dummy semop()\n", (long) getpid());

    } else {                            /* We didn't create the semaphore set */

        if (errno != EEXIST) {          /* Unexpected error from semget() */
            err_exit(errno, "semget 1");

        } else {                        /* Someone else already created it */
            const int MAX_TRIES = 10;
            int j;
            union semun arg;
            struct semid_ds ds;

            semid = semget(key, 1, perms);      /* So just get ID */
            if (semid == -1)
                err_exit(errno, "semget 2");

            fprintf(stderr, "%ld: got semaphore key\n", (long) getpid());
            /* Wait until another process has called semop() */

            arg.buf = &ds;
            for (j = 0; j < MAX_TRIES; j++) {
                fprintf(stderr, "Try %d\n", j);
                if (semctl(semid, 0, IPC_STAT, arg) == -1)
                    err_exit(errno, "semctl 2");

                if (ds.sem_otime != 0)          /* Semop() performed? */
                    break;                      /* Yes, quit loop */
                sleep(1);                       /* If not, wait and retry */
            }

            if (ds.sem_otime == 0)              /* Loop ran to completion! */
                err_exit(errno, "Existing semaphore not initialized");
        }
    }
    return semid;
}


/* Reserve semaphore (blocking), return 0 on success, or -1 with 'errno'
   set to EINTR if operation was interrupted by a signal handler */

/* Reserve semaphore - decrement it by 1 */
int pcsem::dec(int semId)
{
    struct sembuf sops;

    sops.sem_num = 0;
    sops.sem_op = -1;
    sops.sem_flg =  0;

    while (semop(semId, &sops, 1) == -1)
        if (errno != EINTR )
            return -1;

    return 0;
}

int pcsem::dec_nowait(int semId)
{
    struct sembuf sops;

    sops.sem_num = 0;
    sops.sem_op = -1;
    sops.sem_flg =  IPC_NOWAIT;

    while (semop(semId, &sops, 1) == -1)
        if (errno != EINTR )
            return -1;

    return 0;
}

int pcsem::dec_timeout(int semId, struct timespec * timeout)
{
    struct sembuf sops;

    sops.sem_num = 0;
    sops.sem_op = -1;
    sops.sem_flg = 0;

    while ( semtimedop(semId, &sops, 1, timeout) == -1)
        if (errno != EINTR )
            return -1;

    return 0;
}



/* Release semaphore - increment it by 1 */
int pcsem::inc(int semId)
{
    struct sembuf sops;

    sops.sem_num = 0;
    sops.sem_op = 1;
    sops.sem_flg = 0;

    return semop(semId, &sops, 1);
}

void pcsem::remove(int semid) {
    union semun dummy;
    if (semctl(semid, 0, IPC_RMID, dummy) == -1)
        err_exit(errno, "semctl");

}