spin.h

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/*-------------------------------------------------------------------------
 *
 * spin.h
 *     Hardware-independent implementation of spinlocks.
 *
 *
 *  The hardware-independent interface to spinlocks is defined by the
 *  typedef "slock_t" and these macros:
 *
 *  void SpinLockInit(volatile slock_t *lock)
 *      Initialize a spinlock (to the unlocked state).
 *
 *  void SpinLockAcquire(volatile slock_t *lock)
 *      Acquire a spinlock, waiting if necessary.
 *      Time out and abort() if unable to acquire the lock in a
 *      "reasonable" amount of time --- typically ~ 1 minute.
 *
 *  void SpinLockRelease(volatile slock_t *lock)
 *      Unlock a previously acquired lock.
 *
 *  bool SpinLockFree(slock_t *lock)
 *      Tests if the lock is free. Returns TRUE if free, FALSE if locked.
 *      This does *not* change the state of the lock.
 *
 *  Callers must beware that the macro argument may be evaluated multiple
 *  times!
 *
 *  CAUTION: Care must be taken to ensure that loads and stores of
 *  shared memory values are not rearranged around spinlock acquire
 *  and release. This is done using the "volatile" qualifier: the C
 *  standard states that loads and stores of volatile objects cannot
 *  be rearranged *with respect to other volatile objects*. The
 *  spinlock is always written through a volatile pointer by the
 *  spinlock macros, but this is not sufficient by itself: code that
 *  protects shared data with a spinlock MUST reference that shared
 *  data through a volatile pointer.
 *
 *  Keep in mind the coding rule that spinlocks must not be held for more
 *  than a few instructions.  In particular, we assume it is not possible
 *  for a CHECK_FOR_INTERRUPTS() to occur while holding a spinlock, and so
 *  it is not necessary to do HOLD/RESUME_INTERRUPTS() in these macros.
 *
 *  These macros are implemented in terms of hardware-dependent macros
 *  supplied by s_lock.h.  There is not currently any extra functionality
 *  added by this header, but there has been in the past and may someday
 *  be again.
 *
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/spin.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef SPIN_H
#define SPIN_H

#include "storage/s_lock.h"


#define SpinLockInit(lock)  S_INIT_LOCK(lock)

#define SpinLockAcquire(lock) S_LOCK(lock)

#define SpinLockRelease(lock) S_UNLOCK(lock)

#define SpinLockFree(lock)  S_LOCK_FREE(lock)


extern int  SpinlockSemas(void);

#endif   /* SPIN_H */