condvar.c

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/**
 * Unchecked (no BSD invariants) condition variable implementation for
 * dde-internal use. Written from scratch.
 *
 * \author Thomas Friebel <tf13@os.inf.tu-dresden.de>
 */
#include <l4/dde/ddekit/condvar.h>
#include <l4/dde/ddekit/lock.h>
#include <l4/dde/ddekit/memory.h>

#include <l4/log/l4log.h>
#include <l4/semaphore/semaphore.h>
#include <l4/lock/lock.h>

struct ddekit_condvar {
        unsigned waiters;
        unsigned signals;
        l4lock_t lock;
        l4semaphore_t sem;
        l4semaphore_t handshake;
};

ddekit_condvar_t *ddekit_condvar_init() {
        ddekit_condvar_t *cvp;

        cvp = ddekit_simple_malloc(sizeof(*cvp));

        cvp->waiters   = 0;
        cvp->signals   = 0;
        cvp->lock      = L4LOCK_UNLOCKED;
        cvp->sem       = L4SEMAPHORE_INIT(0);
        cvp->handshake = L4SEMAPHORE_INIT(0);

        return cvp;
}

void ddekit_condvar_wait(ddekit_condvar_t *cvp, ddekit_lock_t *mp) {
        ddekit_condvar_wait_timed(cvp, mp, -1);
}

int ddekit_condvar_wait_timed(ddekit_condvar_t *cvp, ddekit_lock_t *mp, int timo) {
        int rval;

        l4lock_lock(&cvp->lock);
        cvp->waiters++;
        l4lock_unlock(&cvp->lock);

        ddekit_lock_unlock(mp);

        if (timo == -1) {
                l4semaphore_down(&cvp->sem);
                rval = 0;
        } else {
                rval = l4semaphore_down_timed(&cvp->sem, timo);
        }

        l4lock_lock(&cvp->lock);
        if (cvp->signals > 0) {
                /* if we timed out, but there is a signal now, consume it */
                if (rval) l4semaphore_down(&cvp->sem);

                l4semaphore_up(&cvp->handshake);
                cvp->signals--;
        }
        cvp->waiters--;
        l4lock_unlock(&cvp->lock);

        ddekit_lock_lock(mp);

        return rval;
}

void ddekit_condvar_signal(ddekit_condvar_t *cvp)
{
        l4lock_lock(&cvp->lock);

        if (cvp->waiters > cvp->signals) {
                cvp->signals++;
                l4semaphore_up(&cvp->sem);
                l4lock_unlock(&cvp->lock);
                l4semaphore_down(&cvp->handshake);
        } else {
                /* nobody left to wakeup */
                l4lock_unlock(&cvp->lock);
        }
}

void ddekit_condvar_broadcast(ddekit_condvar_t *cvp) {
        int waiters;

        l4lock_lock(&cvp->lock);

        waiters = cvp->waiters - cvp->signals;
        if (waiters > 0) {
                int i;

                cvp->signals = cvp->waiters;
                for (i=0; i<waiters; i++) {
                        l4semaphore_up(&cvp->sem);
                }
                l4lock_unlock(&cvp->lock);
                for (i=0; i<waiters; i++) {
                        l4semaphore_down(&cvp->handshake);
                }
        } else {
                l4lock_unlock(&cvp->lock);
        }
}

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