FreeBSD-5.3/lib/libc_r/arch/alpha/_atomic_lock.S

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/*
 * Copyright (c) 1998 John Birrell <jb@cimlogic.com.au>.
 * All rights reserved.
 * copyright Douglas Santry 1996
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the above copyright is retained
 * in the source form.
 *
 * THIS SOFTWARE IS PROVIDED BY Douglas Santry AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE  
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE   
 * ARE DISCLAIMED.  IN NO EVENT SHALL Douglas Santry OR CONTRIBUTORS BE LIABLE 
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL   
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS      
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF  
 * SUCH DAMAGE.    
 *
 * $FreeBSD: src/lib/libc_r/arch/alpha/_atomic_lock.S,v 1.4 2003/07/02 13:27:54 ru Exp $
 *
 */

#include <machine/asm.h>

/*
 * Atomicly lock a location with an identifier provided the location
 * is not currently locked.
 *
 * long _atomic_lock(long *);
 * v0 will contain the return value (zero if lock obtained).
 */
LEAF(_atomic_lock,0)
	LDGP(pv)

0:	ldq_l	v0, 0(a0)	/* read existing lock value */
	mov	1, t0		/* locked value to store */
	stq_c	t0, 0(a0)	/* attempt to store, status in t0 */
	beq	t0, 1f		/* branch foward to optimise prediction */
	mb			/* sync with other processors */
	RET			/* return with v0==0 if lock obtained */
1:	br	0b		/* loop to try again */
END(_atomic_lock)