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/*
* Mach Operating System
* Copyright (c) 1992 Carnegie Mellon University
* All Rights Reserved.
*
* Permission to use, copy, modify and distribute this software and its
* documentation is hereby granted, provided that both the copyright
* notice and this permission notice appear in all copies of the
* software, derivative works or modified versions, and any portions
* thereof, and that both notices appear in supporting documentation.
*
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
* ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
*
* Carnegie Mellon requests users of this software to return to
*
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
* School of Computer Science
* Carnegie Mellon University
* Pittsburgh PA 15213-3890
*
* any improvements or extensions that they make and grant Carnegie Mellon
* the rights to redistribute these changes.
*/
/*
* HISTORY
* $Log: lock.s,v $
* Revision 2.3 93/03/09 10:59:04 danner
* Lost in previous merge:
* Added memory barriers where needed.
* Locks are longs now.
* [93/01/15 af]
*
* Revision 2.2 93/01/14 18:04:31 danner
* Mumble, "try_lock" really means "try_hard_once".
* That is, try hard until you either get it or lose it.
* [92/12/24 af]
* Created a while back.
* [92/12/10 af]
*
*/
#include <mach/alpha/asm.h>
/*
The C interface for this function is
boolean_t
spin_try_lock_sw(m)
long * m;
The function has a slightly different semantics than TAS: it will
return a boolean value that indicates whether the lock was acquired
or not. If not, we'll presume that the user will retry after some
appropriate delay.
*/
.text
.align 4
.set noreorder
LEAF(spin_try_lock,1)
mb
ldq_l t0,0(a0)
or zero,2,v0 /* build lock value */
bne t0,nope /* already set, forget it */
stq_c v0,0(a0) /* see if we still had the lock */
beq v0,yipe /* if we just took an interrupt.. */
RET /* if v0 != 0 then we got it */
nope:
mov zero,v0 /* failed to acquire lock */
RET
yipe: br zero,spin_try_lock /* I love branch predictions.. */
END(spin_try_lock)
LEAF(spin_unlock,1)
mb /* but this might be needed.. */
stq zero,0(a0) /* no need for interlocks (sec 10.5.2) */
mb /* but this might be needed.. */
RET
END(spin_unlock)
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