Working

bertos/mware/resource.c

@@ -0,0 +1,113 @@
+
+#include "resource.h"
+#include <mware/observer.h>
+
+/**
+ * Internal structure for building a priority queue
+ * of processes waiting for the resource to become free.
+ */
+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);
+}
+