lc_sem.c

open source for car navigation in linux

/*
 * Copyright (C) 2002 Ricardo Arroyo <[e-mail]>
 *
 * This code may be used under the terms of Version 2 of the GPL,
 * read the file COPYING for details.
 *
 */
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

#include "lc_debug.h"

#include "lc_sem.h"

/*__________________________________________________________________________*/
/* FUNCTION                iCreateSem (key_t SemKey)                        */
/* DESCRIPTION             Creates and unblocks a semaphore with key SemKey */
/*			                                                    */
/* INPUT PARAMETERS        semKey       Key                                 */
/*                                                                          */
/* OUTPUT PARAMETERS       sem_id (semaphore identifier) or -1 in error     */
/* 			                                                    */
/*__________________________________________________________________________*/

int iCreateSem(key_t SemKey)
{

int sem_id;
struct sembuf sops;

   if ((sem_id = semget(SemKey, 1, 0666 | IPC_CREAT)) == -1)
   {
      fprintf(stderr,"iCreateSem/semget : Key = %d, errno = %d, %s\n",SemKey, errno, strerror(errno));
      sem_id = -1;
   }
   // unblocks semaphore incrementing value
   sops.sem_num = 0;
   sops.sem_op = 1;
   sops.sem_flg = 0;
   if (semop(sem_id, &sops, 1) == -1)
   {
      fprintf(stderr,"iCreateSem/unlock : sem_id = %d, errno = %d, %s\n",sem_id, errno, strerror(errno));
      sem_id = -1;
   }
   if (iDebug & DEP_SEM)
   {
      fprintf(stderr,"iCreateSem : sem_id = %d, Key = %d\n",sem_id, SemKey);
   }
   return(sem_id);
}

/*__________________________________________________________________________*/
/* FUNCTION                iAssignSem (key_t SemKey)                        */
/* DESCRIPTION             Assigns a semaphore identified by key SemKey     */
/*			                                                    */
/* INPUT PARAMETERS        semKey       Key                                 */
/*                                                                          */
/* OUTPUT PARAMETERS       sem_id (semaphore identifier) or -1 in error     */
/* 			                                                    */
/*__________________________________________________________________________*/

int iAssignSem(key_t SemKey)
{
int sem_id;

   if ((sem_id = semget(SemKey, 1, 0666)) == -1)
   {
      fprintf(stderr,"iAssignSem/semget : Key = %d, errno = %d, %s\n",SemKey, errno, strerror(errno));
      sem_id = -1;
   }
   if (iDebug & DEP_SEM)
   {
      fprintf(stderr,"iAssignSem : sem_id = %d, Key = %d\n",sem_id, SemKey);
   }
   return(sem_id);
}


/*__________________________________________________________________________*/
/* FUNCTION                iUnlockSem (int sem_id)                          */
/* DESCRIPTION             Unlocks a semaphore                              */
/*			                                                    */
/* INPUT PARAMETERS        sem_id: semaphore identifier                     */
/*                                                                          */
/* OUTPUT PARAMETERS       0: OK, -1 error                                  */
/* 			                                                    */
/*__________________________________________________________________________*/

int iUnlockSem(int sem_id)
{
int iRetValue; // return value
struct sembuf sops; // semaphore operatios structure
int res;

   sops.sem_num = 0;
   sops.sem_op = 1; // unlocks semaphore
   sops.sem_flg = SEM_UNDO; //undo if process terminates or dies
   if ((res = semop(sem_id, &sops, 1)) == -1)
   {
      fprintf(stderr,"iUnlockSem : sem_id = %d, errno = %d, %s\n",sem_id, errno, strerror(errno));
      iRetValue = -1;
   }
   else
   {
      iRetValue = 0;
   }

   if (iDebug & DEP_SEM)
   {
      fprintf(stderr,"iUnlockSem : sem_id = %d res = %d\n",sem_id,res);
   }
   return(iRetValue);
}


/*__________________________________________________________________________*/
/* FUNCTION                iLockSem (int sem_id)                            */
/* DESCRIPTION             Locks a semaphore                                */
/*			                                                    */
/* INPUT PARAMETERS        sem_id: semaphore identifier                     */
/*                                                                          */
/* OUTPUT PARAMETERS       0: OK, -1 error                                  */
/* 			                                                    */
/*__________________________________________________________________________*/

int iLockSem(int sem_id)
{
int iRetValue; // return value
struct sembuf sops; // semaphore operatios structure
int res;

   sops.sem_num = 0;
   sops.sem_op = -1; // locks semaphore and wait if locked
   sops.sem_flg = SEM_UNDO; //undo if process terminates or dies
   if ((res = semop(sem_id, &sops, 1)) == -1)
   {
      fprintf(stderr,"iLockSem : sem_id = %d, errno = %d, %s\n",sem_id, errno, strerror(errno));
      iRetValue = -1;
   }
   else
   {
      iRetValue = 0;
   }

   if (iDebug & DEP_SEM)
   {
      fprintf(stderr,"iLockSem : sem_id = %d res = %d\n",sem_id,res);
   }
   return(iRetValue);
}

/*__________________________________________________________________________*/
/* FUNCTION                iDelSem (int sem_id)                             */
/* DESCRIPTION             Destroys a semaphore                             */
/*			                                                    */
/* INPUT PARAMETERS        sem_id: semaphore identifier                     */
/*                                                                          */
/* OUTPUT PARAMETERS       0: OK, -1 error                                  */
/* 			                                                    */
/*__________________________________________________________________________*/

int iDelSem(int sem_id)
{
int	iRetValue;

   if (semctl(sem_id,0,IPC_RMID) == -1)
   {
      fprintf(stderr,"iDelSem : sem_id = %d, errno = %d, %s\n",sem_id, errno, strerror(errno));
      iRetValue = -1;
   }
   else
   {
      iRetValue = 0;
   }
   return(iRetValue);
}