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73 lines
2.5 KiB
C
73 lines
2.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* spin.h
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* Hardware-independent implementation of spinlocks.
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*
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*
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* The hardware-independent interface to spinlocks is defined by the
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* typedef "slock_t" and these macros:
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*
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* void SpinLockInit(volatile slock_t *lock)
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* Initialize a spinlock (to the unlocked state).
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*
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* void SpinLockAcquire(volatile slock_t *lock)
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* Acquire a spinlock, waiting if necessary.
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* Time out and abort() if unable to acquire the lock in a
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* "reasonable" amount of time --- typically ~ 1 minute.
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*
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* void SpinLockRelease(volatile slock_t *lock)
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* Unlock a previously acquired lock.
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*
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* bool SpinLockFree(slock_t *lock)
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* Tests if the lock is free. Returns TRUE if free, FALSE if locked.
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* This does *not* change the state of the lock.
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*
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* Callers must beware that the macro argument may be evaluated multiple
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* times!
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*
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* CAUTION: Care must be taken to ensure that loads and stores of
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* shared memory values are not rearranged around spinlock acquire
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* and release. This is done using the "volatile" qualifier: the C
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* standard states that loads and stores of volatile objects cannot
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* be rearranged *with respect to other volatile objects*. The
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* spinlock is always written through a volatile pointer by the
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* spinlock macros, but this is not sufficient by itself: code that
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* protects shared data with a spinlock MUST reference that shared
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* data through a volatile pointer.
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*
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* Keep in mind the coding rule that spinlocks must not be held for more
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* than a few instructions. In particular, we assume it is not possible
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* for a CHECK_FOR_INTERRUPTS() to occur while holding a spinlock, and so
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* it is not necessary to do HOLD/RESUME_INTERRUPTS() in these macros.
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*
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* These macros are implemented in terms of hardware-dependent macros
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* supplied by s_lock.h. There is not currently any extra functionality
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* added by this header, but there has been in the past and may someday
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* be again.
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*
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*
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* Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/spin.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SPIN_H
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#define SPIN_H
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#include "storage/s_lock.h"
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#define SpinLockInit(lock) S_INIT_LOCK(lock)
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#define SpinLockAcquire(lock) S_LOCK(lock)
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#define SpinLockRelease(lock) S_UNLOCK(lock)
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#define SpinLockFree(lock) S_LOCK_FREE(lock)
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extern int SpinlockSemas(void);
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#endif /* SPIN_H */
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