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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) 1996-2012, 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"
#ifndef HAVE_SPINLOCKS
#include "storage/pg_sema.h"
#endif
#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);
extern Size SpinlockSemaSize(void);
#ifndef HAVE_SPINLOCKS
extern void SpinlockSemaInit(PGSemaphore);
extern PGSemaphore SpinlockSemaArray;
#endif
#endif /* SPIN_H */
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