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WebSVN – planix.SVN – Blame – /os/branches/feature_posix/sys/src/libc/port/lock.c – Rev 2

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#include <u.h>
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#include <libc.h>
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void
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lock(Lock *l)
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{
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	if(ainc(&l->key) == 1)
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		return;	/* changed from 0 -> 1: we hold lock */
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	/* otherwise wait in kernel */
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	while(semacquire(&l->sem, 1) < 0){
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		/* interrupted; try again */
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	}
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}
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void
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unlock(Lock *l)
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{
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	if(adec(&l->key) == 0)
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		return;	/* changed from 1 -> 0: no contention */
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	semrelease(&l->sem, 1);
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}
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int
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canlock(Lock *l)
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{
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	if(ainc(&l->key) == 1)
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		return 1;	/* changed from 0 -> 1: success */
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	/* Undo increment (but don't miss wakeup) */
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	if(adec(&l->key) == 0)
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		return 0;	/* changed from 1 -> 0: no contention */
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	semrelease(&l->sem, 1);
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	return 0;
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}