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253 lines
5.8 KiB
C
253 lines
5.8 KiB
C
/*-------------------------------------------------------------------------
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*
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* s_lock.h--
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* This file contains the implementation (if any) for spinlocks.
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*
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* 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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* $Header: /cvsroot/pgsql/src/include/storage/s_lock.h,v 1.34 1998/05/06 23:25:14 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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/*
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* DESCRIPTION
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* The public functions that must be provided are:
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*
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* void S_INIT_LOCK(slock_t *lock)
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*
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* void S_LOCK(slock_t *lock)
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*
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* void S_UNLOCK(slock_t *lock)
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*
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* void S_LOCK_FREE(slock_t *lock)
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* Tests if the lock is free. Returns non-zero if free, 0 if locked.
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*
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* The S_LOCK() macro implements a primitive but still useful random
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* backoff to avoid hordes of busywaiting lockers chewing CPU.
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*
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* Effectively:
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* void
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* S_LOCK(slock_t *lock)
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* {
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* while (TAS(lock))
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* {
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* // back off the cpu for a semi-random short time
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* }
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* }
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*
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* This implementation takes advantage of a tas function written
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* (in assembly language) on machines that have a native test-and-set
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* instruction. Alternative mutex implementations may also be used.
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* This function is hidden under the TAS macro to allow substitutions.
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*
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* #define TAS(lock) tas(lock)
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* int tas(slock_t *lock) // True if lock already set
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*
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* If none of this can be done, POSTGRES will default to using
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* System V semaphores (and take a large performance hit -- around 40%
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* of its time on a DS5000/240 is spent in semop(3)...).
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*
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* NOTES
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* AIX has a test-and-set but the recommended interface is the cs(3)
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* system call. This provides an 8-instruction (plus system call
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* overhead) uninterruptible compare-and-set operation. True
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* spinlocks might be faster but using cs(3) still speeds up the
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* regression test suite by about 25%. I don't have an assembler
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* manual for POWER in any case.
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*
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* There are default implementations for all these macros at the bottom
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* of this file. Check if your platform can use these or needs to
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* override them.
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*
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*/
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#if !defined(S_LOCK_H)
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#define S_LOCK_H
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#include "storage/ipc.h"
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#if defined(HAS_TEST_AND_SET)
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#if defined(linux)
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/***************************************************************************
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* All Linux
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*/
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#if defined(__alpha)
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#define S_UNLOCK(lock) { __asm__("mb"); *(lock) = 0; }
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#endif /* __alpha */
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#else /* linux */
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/***************************************************************************
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* All non Linux
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*/
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#if defined (nextstep)
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/*
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* NEXTSTEP (mach)
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* slock_t is defined as a struct mutex.
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*/
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#define S_LOCK(lock) mutex_lock(lock)
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#define S_UNLOCK(lock) mutex_unlock(lock)
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#define S_INIT_LOCK(lock) mutex_init(lock)
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/* For Mach, we have to delve inside the entrails of `struct mutex'. Ick! */
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#define S_LOCK_FREE(alock) ((alock)->lock == 0)
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#endif /* nextstep */
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#if defined(__sgi)
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/*
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* SGI IRIX 5
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* slock_t is defined as a struct abilock_t, which has a single unsigned long
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* member.
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*
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* This stuff may be supplemented in the future with Masato Kataoka's MIPS-II
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* assembly from his NECEWS SVR4 port, but we probably ought to retain this
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* for the R3000 chips out there.
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*/
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#define TAS(lock) (!acquire_lock(lock))
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#define S_UNLOCK(lock) release_lock(lock)
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#define S_INIT_LOCK(lock) init_lock(lock)
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#define S_LOCK_FREE(lock) (stat_lock(lock) == UNLOCKED)
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#endif /* __sgi */
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#if defined(__alpha)
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/*
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* OSF/1 (Alpha AXP)
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*
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* Note that slock_t on the Alpha AXP is msemaphore instead of char
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* (see storage/ipc.h).
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*/
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#define TAS(lock) (msem_lock((lock), MSEM_IF_NOWAIT) < 0)
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#define S_UNLOCK(lock) msem_unlock((lock), 0)
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#define S_INIT_LOCK(lock) msem_init((lock), MSEM_UNLOCKED)
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#define S_LOCK_FREE(lock) (!(lock)->msem_state)
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#endif /* __alpha */
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#if defined(_AIX)
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/*
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* AIX (POWER)
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*
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* Note that slock_t on POWER/POWER2/PowerPC is int instead of char
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* (see storage/ipc.h).
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*/
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#define TAS(lock) cs((int *) (lock), 0, 1)
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#endif /* _AIX */
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#if defined(__hpux)
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/*
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* HP-UX (PA-RISC)
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*
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* Note that slock_t on PA-RISC is a structure instead of char
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* (see storage/ipc.h).
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*
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* a "set" slock_t has a single word cleared. a "clear" slock_t has
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* all words set to non-zero. tas() in tas.s
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*/
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static slock_t clear_lock =
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{-1, -1, -1, -1};
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#define S_UNLOCK(lock) (*(lock) = clear_lock) /* struct assignment */
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#define S_LOCK_FREE(lock) ( *(int *) (((long) (lock) + 15) & ~15) != 0)
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#endif /* __hpux */
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#endif /* else defined(linux) */
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/****************************************************************************
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* Default Definitions - override these above as needed.
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*/
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#if !defined(S_LOCK)
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#include <sys/time.h>
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#define S_NSPINCYCLE 16
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#define S_MAX_BUSY 1000 * S_NSPINCYCLE
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extern int s_spincycle[];
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extern void s_lock_stuck(slock_t *lock, char *file, int line);
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#if defined(S_LOCK_DEBUG)
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extern void s_lock(slock_t *lock);
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#define S_LOCK(lock) s_lock(lock, __FILE__, __LINE__)
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#else /* S_LOCK_DEBUG */
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#define S_LOCK(lock) if (1) { \
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int spins = 0; \
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while (TAS(lock)) { \
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struct timeval delay; \
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delay.tv_sec = 0; \
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delay.tv_usec = s_spincycle[spins++ % S_NSPINCYCLE]; \
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(void) select(0, NULL, NULL, NULL, &delay); \
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if (spins > S_MAX_BUSY) { \
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/* It's been well over a minute... */ \
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s_lock_stuck(lock, __FILE__, __LINE__); \
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} \
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} \
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} else
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#endif /* S_LOCK_DEBUG */
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#endif /* S_LOCK */
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#if !defined(S_LOCK_FREE)
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#define S_LOCK_FREE(lock) ((*lock) == 0)
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#endif /* S_LOCK_FREE */
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#if !defined(S_UNLOCK)
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#define S_UNLOCK(lock) (*(lock) = 0)
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#endif /* S_UNLOCK */
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#if !defined(S_INIT_LOCK)
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#define S_INIT_LOCK(lock) S_UNLOCK(lock)
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#endif /* S_INIT_LOCK */
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#if !defined(TAS)
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int tas(slock_t *lock); /* port/.../tas.s, or s_lock.c */
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#define TAS(lock) tas(lock)
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#endif /* TAS */
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#endif /* HAS_TEST_AND_SET */
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#endif /* S_LOCK_H */
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