/*
 * Simple semaphore implementation, P() and V().
 *
 * Copyright (C) 2011  Simon Ruderich
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "sem.h"

#include <stdlib.h>
#include <pthread.h>


struct SEM {
    pthread_mutex_t mutex;
    pthread_cond_t  condition;
    int value;
};

SEM *sem_init(int init_value) {
    SEM *sem = (SEM *)malloc(sizeof(SEM));
    if (NULL == sem) {
        return NULL;
    }

    if (0 != pthread_mutex_init(&sem->mutex, NULL)) {
        free(sem);
        return NULL;
    }
    if (0 != pthread_cond_init(&sem->condition, NULL)) {
        pthread_mutex_destroy(&sem->mutex);
        free(sem);
        return NULL;
    }

    sem->value = init_value;
    return sem;
}

int sem_del(SEM *sem) {
    if (NULL == sem) {
        return 0;
    }

    if (0 != pthread_mutex_destroy(&sem->mutex)) {
        free(sem);
        return -1;
    }
    if (0 != pthread_cond_destroy(&sem->condition)) {
        free(sem);
        return -1;
    }

    free(sem);
    return 0;
}

void P(SEM *sem) {
    pthread_mutex_lock(&sem->mutex);
    while (0 == sem->value) {
        pthread_cond_wait(&sem->condition, &sem->mutex);
    }
    sem->value--;
    pthread_mutex_unlock(&sem->mutex);
}

void V(SEM *sem) {
    pthread_mutex_lock(&sem->mutex);
    sem->value++;
    pthread_cond_broadcast(&sem->condition);
    pthread_mutex_unlock(&sem->mutex);
}