/*  * This file is part of the UCB release of Plan 9. It is subject to the license * terms in the LICENSE file found in the top-level directory of this * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No * part of the UCB release of Plan 9, including this file, may be copied, * modified, propagated, or distributed except according to the terms contained * in the LICENSE file. */ #include <u.h>#include <libc.h> voidlock(Lock *l){	if(ainc(&l->key) == 1)		return;	/* changed from 0 -> 1: we hold lock */	/* otherwise wait in kernel */	while(semacquire(&l->sem, 1) < 0){		/* interrupted; try again */	}} voidunlock(Lock *l){	if(adec(&l->key) == 0)		return;	/* changed from 1 -> 0: no contention */	semrelease(&l->sem, 1);} intcanlock(Lock *l){	if(ainc(&l->key) == 1)		return 1;	/* changed from 0 -> 1: success */	/* Undo increment (but don't miss wakeup) */	if(adec(&l->key) == 0)		return 0;	/* changed from 1 -> 0: no contention */	semrelease(&l->sem, 1);	return 0;}