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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 */