resource.c

#include "resource.h"
#include <mware/observer.h>

typedef struct ResourceWaiter
{
    PriNode link;
    struct Observer *owner;

} ResourceWaiter;


bool ResMan_Alloc(Resource *res, int pri, ResMan_time_t timeout, struct Observer *releaseRequest)
{
    bool success = false;

    ASSERT(releaseRequest);

    sem_obtain(&res->lock);

    if (res->owner == releaseRequest)
    {
        // Already ours
        res->pri = pri;
        success = true;
    }
    else if (!res->owner)
    {
        // Trivial acquire: nobody was owning the resource
        res->pri = pri;
        res->owner = releaseRequest;
        success = true;
    }
    else
    {
        ResourceWaiter waiter;

        // Setup waiter structure and enqueue it to resource
        waiter.owner = releaseRequest;
        waiter.link.pri = pri;
        LIST_ENQUEUE(&res->queue, &waiter.link);

        // Resource busy: are we eligible for preemption?
        if ((res->pri < pri) && res->owner->event)
            res->owner->event(EVENT_RELEASE, res);

        // Wait in the queue until the timeout occurs.
        do
        {
            sem_release(&res->lock);
            // TODO: use a semaphore here instead
            ResMan_sleep();
            sem_obtain(&res->lock);

            // Check for ownership
            if (res->owner == releaseRequest)
            {
                success = true;
                break;
            }
        }
        while (timeout--);

        // Remove pending waiter
        if (!success)
            REMOVE(&waiter.link.link);
    }

    sem_release(&res->lock);
    return success;
}

void ResMan_Free(Resource *res)
{
    ResourceWaiter *waiter;

    sem_obtain(&res->lock);


    ASSERT(res->owner);
    //TODO: check for real owner calling free

    // Check for new owner candidates.
    if ((waiter = (ResourceWaiter *)list_remHead(&res->queue)))
    {
        // Transfer ownership of the resource
        res->owner = waiter->owner;
        res->pri = waiter->link.pri;
        //ResMan_wakeup(waiter);
    }
    else
    {
        // Nobody waiting, free the resource
        res->owner = NULL;
        res->pri = -1;
    }

    sem_release(&res->lock);
}

void ResMan_Init(Resource *res)
{
    res->owner = NULL;
    res->pri = -1;

    sem_init(&res->lock);
    LIST_INIT(&res->queue);
}