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#include <u.h>
#include <libc.h>
void
lock(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 */
}
}
void
unlock(Lock *l)
{
if(adec(&l->key) == 0)
return; /* changed from 1 -> 0: no contention */
semrelease(&l->sem, 1);
}
int
canlock(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;
}
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