shm_locking.c

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/* {{{ Initial headers */
/*
 * $LastChangedDate: 2003-11-27 01:55:17 +0100 (Thu, 27 Nov 2003) $
 * $LastChangedRevision: 5 $
 * $LastChangedBy: ckruse $
 *
 */
/* }}} */

/* {{{ Includes */
#include "config.h"
#include "defines.h"

#ifdef CF_SHARED_MEM

#include <sys/types.h>

#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>

#include <unistd.h>

#include "semaphores.h"
#include "shm_locking.h"
/* }}} */

int shm_lock_exclusive(int semid) {
  /* decrease writer */
  if(CF_SEM_UNLOCK(semid,CF_WRITER_SEM) == -1) return -1;

  /* wait until reader number is 0 */
  if(CF_SEM_WAITZERO(semid,CF_READER_SEM) == -1) {
    CF_SEM_LOCK(semid,CF_WRITER_SEM);
    return -1;
  }

  /* lock semaphore set */
  if(CF_SEM_LOCK(semid,CF_LOCK_SEM) == -1) {
    CF_SEM_LOCK(semid,CF_WRITER_SEM);
    return -1;
  }

  return 0;
}

int shm_unlock_exclusive(int semid) {
  if(CF_SEM_UNLOCK(semid,0) == -1) return -1;

  return CF_SEM_LOCK(semid,2);
}

int shm_lock_shared(int semid) {
  if(CF_SEM_WAITZERO(semid,CF_WRITER_SEM) == -1) return -1;

  return CF_SEM_UNLOCK(semid,CF_READER_SEM);
}

int shm_unlock_shared(int semid) {
  return CF_SEM_LOCK(semid,CF_READER_SEM);
}

#endif

/* eof */

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