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e25626677f
A later change will require atomic support, so it wouldn't make sense for a hypothetical new system not to be able to implement spinlocks. Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> (concept, not the patch) Reviewed-by: Andres Freund <andres@anarazel.de> (concept, not the patch) Discussion: https://postgr.es/m/3351991.1697728588%40sss.pgh.pa.us
66 lines
2.1 KiB
C
66 lines
2.1 KiB
C
/*-------------------------------------------------------------------------
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*
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* spin.h
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* API for spinlocks.
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*
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*
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* The interface to spinlocks is defined by the typedef "slock_t" and
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* 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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* Load and store operations in calling code are guaranteed not to be
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* reordered with respect to these operations, because they include a
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* compiler barrier. (Before PostgreSQL 9.5, callers needed to use a
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* volatile qualifier to access data protected by spinlocks.)
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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) 1996-2024, 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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#endif /* SPIN_H */
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