postgresql/src/include/storage/s_lock.h

/*-------------------------------------------------------------------------
 *
 * s_lock.h--
 *	   This file contains the implementation (if any) for spinlocks.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/include/storage/s_lock.h,v 1.51 1998/10/01 01:53:50 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

/*
 *	 DESCRIPTION
 *		The public macros that must be provided are:
 *
 *		void S_INIT_LOCK(slock_t *lock)
 *
 *		void S_LOCK(slock_t *lock)
 *
 *		void S_UNLOCK(slock_t *lock)
 *
 *		void S_LOCK_FREE(slock_t *lock)
 *			Tests if the lock is free. Returns non-zero if free, 0 if locked.
 *
 *		The S_LOCK() macro	implements a primitive but still useful random
 *		backoff to avoid hordes of busywaiting lockers chewing CPU.
 *
 *		Effectively:
 *		void
 *		S_LOCK(slock_t *lock)
 *		{
 *			while (TAS(lock))
 *			{
 *			// back off the cpu for a semi-random short time
 *			}
 *		}
 *
 *		This implementation takes advantage of a tas function written
 *		(in assembly language) on machines that have a native test-and-set
 *		instruction. Alternative mutex implementations may also be used.
 *		This function is hidden under the TAS macro to allow substitutions.
 *
 *		#define TAS(lock) tas(lock)
 *		int tas(slock_t *lock)		// True if lock already set
 *
 *		There are default implementations for all these macros at the bottom
 *		of this file. Check if your platform can use these or needs to
 *		override them.
 *
 *	NOTES
 *		If none of this can be done, POSTGRES will default to using
 *		System V semaphores (and take a large performance hit -- around 40%
 *		of its time on a DS5000/240 is spent in semop(3)...).
 *
 *		AIX has a test-and-set but the recommended interface is the cs(3)
 *		system call.  This provides an 8-instruction (plus system call
 *		overhead) uninterruptible compare-and-set operation.  True
 *		spinlocks might be faster but using cs(3) still speeds up the
 *		regression test suite by about 25%.  I don't have an assembler
 *		manual for POWER in any case.
 *
 */
#if !defined(S_LOCK_H)
#define S_LOCK_H

#include "storage/ipc.h"

#if defined(HAS_TEST_AND_SET)


#if defined(__GNUC__)
/*************************************************************************
 * All the gcc inlines
 */

#if defined(__alpha)
#define TAS(lock) tas(lock)
#define S_UNLOCK(lock) { __asm__("mb"); *(lock) = 0; }

static __inline__ int
tas(volatile slock_t *lock)
{
	register slock_t _res;

__asm__("    ldq   $0, %0              \n\
                 bne   $0, already_set     \n\
                 ldq_l $0, %0	           \n\
                 bne   $0, already_set     \n\
                 or    $31, 1, $0          \n\
                 stq_c $0, %0	           \n\
                 beq   $0, stqc_fail       \n\
        success: bis   $31, $31, %1        \n\
                 mb		                   \n\
                 jmp   $31, end	           \n\
      stqc_fail: or    $31, 1, $0	       \n\
    already_set: bis   $0, $0, %1	       \n\
            end: nop      ": "=m"(*lock), "=r"(_res): :"0");

	return (int) _res;
}

#endif	 /* __alpha */



#if defined(i386)
#define TAS(lock) tas(lock)

static __inline__ int
tas(volatile slock_t *lock)
{
	register slock_t _res = 1;

__asm__("lock; xchgb %0,%1": "=q"(_res), "=m"(*lock):"0"(_res));
	return (int) _res;
}

#endif	 /* i386 */



#if defined(sparc)
#define TAS(lock) tas(lock)

static __inline__ int
tas(volatile slock_t *lock)
{
	register slock_t _res = 1;

	__asm__("ldstub [%2], %0" \
:			"=r"(_res), "=m"(*lock) \
:			"r"(lock));
	return (int) _res;
}

#endif	 /* sparc */



#if defined(NEED_VAX_TAS_ASM)
/*
 * VAXen -- even multiprocessor ones
 * (thanks to Tom Ivar Helbekkmo)
 */
#define TAS(lock) tas(lock)

typedef unsigned char slock_t;

static __inline__ int
tas(volatile slock_t *lock)
{
	register	_res;

	__asm__("	movl $1, r0 \
			bbssi $0, (%1), 1 f \
			clrl r0 \
1:			movl r0, %0 "
:			"=r"(_res)			/* return value, in register */
:			"r"(lock)			/* argument, 'lock pointer', in register */
:			"r0");				/* inline code uses this register */
	return (int) _res;
}

#endif	 /* NEED_VAX_TAS_ASM */




#else							/* __GNUC__ */
/***************************************************************************
 * All non gcc
 */

#if defined(__alpha)
/*
 * OSF/1 (Alpha AXP)
 *
 * Note that slock_t on the Alpha AXP is msemaphore instead of char
 * (see storage/ipc.h).
 */
#define TAS(lock)	(msem_lock((lock), MSEM_IF_NOWAIT) < 0)
#define S_UNLOCK(lock)	msem_unlock((lock), 0)
#define S_INIT_LOCK(lock)	msem_init((lock), MSEM_UNLOCKED)
#define S_LOCK_FREE(lock)	(!(lock)->msem_state)
#endif	 /* __alpha */



#if defined(NEED_I386_TAS_ASM)
/* non gcc i386 based things */

#if defined(USE_UNIVEL_CC)
#define TAS(lock)	tas(lock)

asm int
tas(slock_t *s_lock)
{
/* UNIVEL wants %mem in column 1, so we don't pg_indent this file */
%mem s_lock
	pushl %ebx
	movl s_lock, %ebx
	movl $255, %eax
	lock
	xchgb %al, (%ebx)
	popl %ebx
}

#endif	 /* USE_UNIVEL_CC */

#endif	 /* NEED_I386_TAS_ASM */



#if defined(NEED_NS32K_TAS_ASM)

#define S_LOCK(lock)				\
{						\
	slock_t res = 1;				\
	while (res) {				\
	  __asm__("movqd 0, r0");			\
	  __asm__("sbitd r0, %0" : "=m"(*lock));	\
	  __asm__("sprb us, %0" : "=r" (res));	\
	  res = ((res >> 5) & 1);			\
	}						\
}

#endif	 /* NEED_NS32K_TAS_ASM */


#endif	 /* defined(__GNUC__) */



/*************************************************************************
 * These are the platforms that have common code for gcc and non-gcc
 */

#if defined(__hpux)
/*
 * HP-UX (PA-RISC)
 *
 * Note that slock_t on PA-RISC is a structure instead of char
 * (see include/port/hpux.h).
 *
 * a "set" slock_t has a single word cleared.  a "clear" slock_t has
 * all words set to non-zero. tas() in tas.s
 */

#define S_UNLOCK(lock) \
{ \
	volatile slock_t *lock_ = (volatile slock_t *) (lock); \
	lock_->sema[0] = lock_->sema[1] = lock_->sema[2] = lock_->sema[3] = -1; \
}

#define S_LOCK_FREE(lock)	( *(int *) (((long) (lock) + 15) & ~15) != 0)

#endif	 /* __hpux */


#if defined(__sgi)
/*
 * SGI IRIX 5
 * slock_t is defined as a struct abilock_t, which has a single unsigned long
 * member.
 *
 * This stuff may be supplemented in the future with Masato Kataoka's MIPS-II
 * assembly from his NECEWS SVR4 port, but we probably ought to retain this
 * for the R3000 chips out there.
 */
#include <mutex.h>
#define TAS(lock)	(test_and_set(lock,1))
#define S_UNLOCK(lock)	(test_then_and(lock,0))
#define S_INIT_LOCK(lock)	(test_then_and(lock,0))
#define S_LOCK_FREE(lock)	(test_then_add(lock,0) == 0)
#endif	 /* __sgi */

#if defined(sinix)
/*
 * SINIX / Reliant UNIX 
 * slock_t is defined as a struct abilock_t, which has a single unsigned long
 * member. (Basically same as SGI)
 *
 */
#define TAS(lock)	(!acquire_lock(lock))
#define S_UNLOCK(lock)	release_lock(lock)
#define S_INIT_LOCK(lock)	init_lock(lock)
#define S_LOCK_FREE(lock)	(stat_lock(lock) == UNLOCKED)
#endif	 /* sinix */
 

#if defined(_AIX)
/*
 * AIX (POWER)
 *
 * Note that slock_t on POWER/POWER2/PowerPC is int instead of char
 * (see storage/ipc.h).
 */
#define TAS(lock)	cs((int *) (lock), 0, 1)
#endif	 /* _AIX */


#if defined (nextstep)
/*
 * NEXTSTEP (mach)
 * slock_t is defined as a struct mutex.
 */

#define S_LOCK(lock)	mutex_lock(lock)
#define S_UNLOCK(lock)	mutex_unlock(lock)
#define S_INIT_LOCK(lock)	mutex_init(lock)
/* For Mach, we have to delve inside the entrails of `struct mutex'.  Ick! */
#define S_LOCK_FREE(alock)	((alock)->lock == 0)
#endif	 /* nextstep */




/****************************************************************************
 * Default Definitions - override these above as needed.
 */

#if !defined(S_LOCK)
extern void s_lock(volatile slock_t *lock, const char *file, const int line);

#define S_LOCK(lock) \
	do { \
		if (TAS((volatile slock_t *) lock)) \
			s_lock((volatile slock_t *) lock, __FILE__, __LINE__); \
	} while (0)
#endif	 /* S_LOCK */

#if !defined(S_LOCK_FREE)
#define S_LOCK_FREE(lock)	(*(lock) == 0)
#endif	 /* S_LOCK_FREE */

#if !defined(S_UNLOCK)
#define S_UNLOCK(lock)		(*(lock) = 0)
#endif	 /* S_UNLOCK */

#if !defined(S_INIT_LOCK)
#define S_INIT_LOCK(lock)	S_UNLOCK(lock)
#endif	 /* S_INIT_LOCK */

#if !defined(TAS)
int			tas(volatile slock_t *lock);		/* port/.../tas.s, or
												 * s_lock.c */

#define TAS(lock)		tas((volatile slock_t *) lock)
#endif	 /* TAS */

#endif	 /* HAS_TEST_AND_SET */
#endif	 /* S_LOCK_H */