Logo Search packages:      
Sourcecode: postgresql-8.4 version File versions

spin.c

/*-------------------------------------------------------------------------
 *
 * spin.c
 *       Hardware-independent implementation of spinlocks.
 *
 *
 * For machines that have test-and-set (TAS) instructions, s_lock.h/.c
 * define the spinlock implementation.    This file contains only a stub
 * implementation for spinlocks using PGSemaphores.  Unless semaphores
 * are implemented in a way that doesn't involve a kernel call, this
 * is too slow to be very useful :-(
 *
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/storage/lmgr/spin.c,v 1.24 2009/01/01 17:23:48 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "miscadmin.h"
#include "storage/lwlock.h"
#include "storage/spin.h"


#ifdef HAVE_SPINLOCKS

/*
 * Report number of semaphores needed to support spinlocks.
 */
int
SpinlockSemas(void)
{
      return 0;
}
#else                                     /* !HAVE_SPINLOCKS */

/*
 * No TAS, so spinlocks are implemented as PGSemaphores.
 */


/*
 * Report number of semaphores needed to support spinlocks.
 */
int
SpinlockSemas(void)
{
      /*
       * It would be cleaner to distribute this logic into the affected modules,
       * similar to the way shmem space estimation is handled.
       *
       * For now, though, we just need a few spinlocks (10 should be plenty)
       * plus one for each LWLock and one for each buffer header.
       */
      return NumLWLocks() + NBuffers + 10;
}

/*
 * s_lock.h hardware-spinlock emulation
 */

void
s_init_lock_sema(volatile slock_t *lock)
{
      PGSemaphoreCreate((PGSemaphore) lock);
}

void
s_unlock_sema(volatile slock_t *lock)
{
      PGSemaphoreUnlock((PGSemaphore) lock);
}

bool
s_lock_free_sema(volatile slock_t *lock)
{
      /* We don't currently use S_LOCK_FREE anyway */
      elog(ERROR, "spin.c does not support S_LOCK_FREE()");
      return false;
}

int
tas_sema(volatile slock_t *lock)
{
      /* Note that TAS macros return 0 if *success* */
      return !PGSemaphoreTryLock((PGSemaphore) lock);
}

#endif   /* !HAVE_SPINLOCKS */

Generated by  Doxygen 1.6.0   Back to index