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#include "sched.h"
#include <core/sys.h>
#include <mem/mem.h>
// Lower priority numbers have high priority. Priorities must start at 0.
#define PRIORITIES 4 // we have 4 priority levels
#define PRIORITY(t) (t->process->privilege) //get priority for a thread
extern struct thread *idle_thread;
static struct thread *queue[PRIORITIES] = {0}, *last[PRIORITIES] = {0};
/* For internal use only. Enqueues specified thread in specified priority queue. */
static void sched_enqueueIn(struct thread *t, int qid) {
t->queue_next = 0;
if (queue[qid] == 0) {
queue[qid] = last[qid] = t;
} else {
last[qid]->queue_next = t;
last[qid] = t;
}
}
/* For internal use only. Pops a thread from specified queue, if available. */
static struct thread *sched_dequeueFrom(int qid) {
if (queue[qid] == 0) return 0;
struct thread *it = queue[qid];
ASSERT((it->queue_next == 0 && it == last[qid]) || it != last[qid]);
queue[qid] = it->queue_next;
if (queue[qid] == 0) last[qid] = 0;
return it;
}
/* Used by task.c. Enqueus a thread in the corresponding priority queue. */
void sched_enqueue(struct thread *t) {
if (t == idle_thread) return;
sched_enqueueIn(t, PRIORITY(t));
}
/* Used by task.c. Pops a thread from the lowest priority non-empty queue. */
struct thread *sched_dequeue() {
struct thread *it = 0;
int i;
for (i = 0; i < PRIORITIES; i++) {
it = sched_dequeueFrom(i);
if (it != 0) break;
}
if (it == 0) return idle_thread;
return it;
}
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