/*
 * Project 3 - Shared memory and semaphores.
 * Dr. Silaghi's Operating System Concepts.
 * semaphore.c - Common semaphore functions.
 * By: Michael Rywalt - 2569
 */
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <unistd.h>
#include <syslog.h>
#include "common.h"

/* Necessary definitions. */
#define NSEMS 1

/* Variables for external use. */
int iSemaphoreId;
struct sembuf WaitMutex   = {SEMMUTEX, -1, 0};
struct sembuf SignalMutex = {SEMMUTEX,  1, 0};

union semun
{
	int iVal;
	struct semid_ds *buf;
	unsigned short *uwArray;
};

/*****************
 * InitSemaphore *
 *****************
 * 
 * Function: InitSemaphore
 *
 * Purpose: Initialize the use of semaphores.
 *
 * Parameters: None.
 *
 * Returns: Semaphore ID.
 */
void InitSemaphore()
{
	key_t key;
	union semun uArg;

	syslog(LOG_INFO, " [%s] Initializing semaphores.", __FUNCTION__);

	if((key = ftok(PROJECT_KEY, PROJECT_ID)) == -1)
	{
		syslog(LOG_INFO, " [%s] Error getting key.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	/* Create the semaphore set. */
	if((iSemaphoreId = semget(key, NSEMS, 0644 | IPC_CREAT)) == -1)
	{
		syslog(LOG_INFO, " [%s] Error getting semaphore.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	/* Initialize the MUTEX semaphore. */
	uArg.iVal = 1;
	if(semctl(iSemaphoreId, SEMMUTEX, SETVAL, uArg) == -1)
	{
		syslog(LOG_INFO, " [%s] Error setting MUTEX semaphore.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}
}

/********************
 * DestroySemaphore *
 ********************
 * 
 * Function: DestroySemaphore
 *
 * Purpose: To uninitialize the use of semaphores.
 *
 * Parameters: None.
 *
 * Returns: Nothing.
 */
void DestroySemaphore()
{
	key_t key;
	union semun uArg;

	syslog(LOG_INFO, " [%s] Uninitializing semaphores.", __FUNCTION__);
	
	if((key = ftok(PROJECT_KEY, PROJECT_ID)) == -1)
	{
		syslog(LOG_INFO, " [%s] Error getting Key.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	/* Get the semaphore. */
	if((iSemaphoreId = semget(key, 1, 0)) == -1)
	{
		syslog(LOG_INFO, " [%s] Semget: Semaphore doesn't or no longer exists.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	/* Remove the MUTEX semaphore. */
	if(semctl(iSemaphoreId, SEMMUTEX, IPC_RMID, uArg) == -1)
	{
		syslog(LOG_INFO, " [%s] Error removing MUTEX semaphore.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}
}