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95 lines
2.0 KiB
C
95 lines
2.0 KiB
C
/*-------------------------------------------------------------------------
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*
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* spin.c
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* Hardware-independent implementation of spinlocks.
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*
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*
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* For machines that have test-and-set (TAS) instructions, s_lock.h/.c
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* define the spinlock implementation. This file contains only a stub
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* implementation for spinlocks using PGSemaphores. Unless semaphores
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* are implemented in a way that doesn't involve a kernel call, this
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* is too slow to be very useful :-(
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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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*
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* IDENTIFICATION
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* src/backend/storage/lmgr/spin.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "miscadmin.h"
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#include "storage/lwlock.h"
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#include "storage/spin.h"
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#ifdef HAVE_SPINLOCKS
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/*
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* Report number of semaphores needed to support spinlocks.
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*/
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int
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SpinlockSemas(void)
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{
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return 0;
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}
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#else /* !HAVE_SPINLOCKS */
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/*
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* No TAS, so spinlocks are implemented as PGSemaphores.
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*/
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/*
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* Report number of semaphores needed to support spinlocks.
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*/
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int
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SpinlockSemas(void)
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{
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/*
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* It would be cleaner to distribute this logic into the affected modules,
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* similar to the way shmem space estimation is handled.
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*
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* For now, though, we just need a few spinlocks (10 should be plenty)
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* plus one for each LWLock and one for each buffer header.
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*/
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return NumLWLocks() + NBuffers + 10;
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}
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/*
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* s_lock.h hardware-spinlock emulation
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*/
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void
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s_init_lock_sema(volatile slock_t *lock)
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{
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PGSemaphoreCreate((PGSemaphore) lock);
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}
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void
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s_unlock_sema(volatile slock_t *lock)
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{
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PGSemaphoreUnlock((PGSemaphore) lock);
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}
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bool
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s_lock_free_sema(volatile slock_t *lock)
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{
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/* We don't currently use S_LOCK_FREE anyway */
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elog(ERROR, "spin.c does not support S_LOCK_FREE()");
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return false;
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}
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int
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tas_sema(volatile slock_t *lock)
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{
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/* Note that TAS macros return 0 if *success* */
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return !PGSemaphoreTryLock((PGSemaphore) lock);
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}
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#endif /* !HAVE_SPINLOCKS */
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