Subversion Repositories planix.SVN

#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;
}