feat: Only dequeue request if actually earlier

runtime/include/global_request_scheduler.h

@@ -1,15 +1,19 @@
 #pragma once
 
+#include <stdint.h>
+
 #include "sandbox_request.h"
 
 /* Returns pointer back if successful, null otherwise */
 typedef struct sandbox_request *(*global_request_scheduler_add_fn_t)(void *);
 typedef int (*global_request_scheduler_remove_fn_t)(struct sandbox_request **);
+typedef int (*global_request_scheduler_remove_if_earlier_fn_t)(struct sandbox_request **, uint64_t);
 typedef uint64_t (*global_request_scheduler_peek_fn_t)(void);
 
 struct global_request_scheduler_config {
 	global_request_scheduler_add_fn_t               add_fn;
 	global_request_scheduler_remove_fn_t            remove_fn;
+	global_request_scheduler_remove_if_earlier_fn_t remove_if_earlier_fn;
 	global_request_scheduler_peek_fn_t              peek_fn;
 };
 
@@ -17,4 +21,5 @@ struct global_request_scheduler_config {
 void                    global_request_scheduler_initialize(struct global_request_scheduler_config *config);
 struct sandbox_request *global_request_scheduler_add(struct sandbox_request *);
 int                     global_request_scheduler_remove(struct sandbox_request **);
+int                     global_request_scheduler_remove_if_earlier(struct sandbox_request **, uint64_t targed_deadline);
 uint64_t                global_request_scheduler_peek();

runtime/include/priority_queue.h

@@ -40,6 +40,7 @@ priority_queue_is_empty(struct priority_queue *self)
 void priority_queue_initialize(struct priority_queue *self, priority_queue_get_priority_fn_t get_priority_fn);
 int  priority_queue_enqueue(struct priority_queue *self, void *value);
 int  priority_queue_dequeue(struct priority_queue *self, void **dequeued_element);
+int  priority_queue_dequeue_if_earlier(struct priority_queue *self, void **dequeued_element, uint64_t target_deadline);
 int  priority_queue_length(struct priority_queue *self);
 uint64_t priority_queue_peek(struct priority_queue *self);
 int      priority_queue_delete(struct priority_queue *self, void *value);

runtime/src/global_request_scheduler.c

@@ -61,6 +61,20 @@ global_request_scheduler_remove(struct sandbox_request **removed_sandbox)
 	return global_request_scheduler.remove_fn(removed_sandbox);
 }
 
+/**
+ * Removes a sandbox request according to the scheduling policy of the variant
+ * @param removed_sandbox where to write the adddress of the removed sandbox
+ * @param target_deadline the deadline that must be validated before dequeuing
+ * @returns 0 if successfully returned a sandbox request, -ENOENT if empty or if no element meets target_deadline,
+ * -EAGAIN if atomic operation unsuccessful
+ */
+int
+global_request_scheduler_remove_if_earlier(struct sandbox_request **removed_sandbox, uint64_t target_deadline)
+{
+	assert(removed_sandbox != NULL);
+	return global_request_scheduler.remove_if_earlier_fn(removed_sandbox, target_deadline);
+}
+
 /**
  * Peeks at the priority of the highest priority sandbox request
  * @returns highest priority

runtime/src/global_request_scheduler_deque.c

@@ -36,6 +36,14 @@ global_request_scheduler_deque_remove(struct sandbox_request **removed_sandbox_r
 	return deque_steal_sandbox(global_request_scheduler_deque, removed_sandbox_request);
 }
 
+static int
+global_request_scheduler_deque_remove_if_earlier(struct sandbox_request **removed_sandbox_request,
+                                                 uint64_t                 target_deadline)
+{
+	panic("Deque variant does not support this call\n");
+	return -1;
+}
+
 void
 global_request_scheduler_deque_initialize()
 {
@@ -46,8 +54,11 @@ global_request_scheduler_deque_initialize()
 	deque_init_sandbox(global_request_scheduler_deque, RUNTIME_MAX_SANDBOX_REQUEST_COUNT);
 
 	/* Register Function Pointers for Abstract Scheduling API */
-	struct global_request_scheduler_config config = { .add_fn    = global_request_scheduler_deque_add,
+	struct global_request_scheduler_config config = {
-		                                          .remove_fn = global_request_scheduler_deque_remove };
+		.add_fn               = global_request_scheduler_deque_add,
+		.remove_fn            = global_request_scheduler_deque_remove,
+		.remove_if_earlier_fn = global_request_scheduler_deque_remove_if_earlier
+	};
 
 	global_request_scheduler_initialize(&config);
 }

runtime/src/global_request_scheduler_minheap.c

@@ -37,6 +37,20 @@ global_request_scheduler_minheap_remove(struct sandbox_request **removed_sandbox
 	return priority_queue_dequeue(&global_request_scheduler_minheap, (void **)removed_sandbox_request);
 }
 
+/**
+ * @param removed_sandbox_request pointer to set to removed sandbox request
+ * @param target_deadline the deadline that the request must be earlier than to dequeue
+ * @returns 0 if successful, -ENOENT if empty or if request isn't earlier than target_deadline
+ */
+int
+global_request_scheduler_minheap_remove_if_earlier(struct sandbox_request **removed_sandbox_request,
+                                                   uint64_t                 target_deadline)
+{
+	assert(!software_interrupt_is_enabled());
+	return priority_queue_dequeue_if_earlier(&global_request_scheduler_minheap, (void **)removed_sandbox_request,
+	                                         target_deadline);
+}
+
 /**
  * Peek at the priority of the highest priority task without having to take the lock
  * Because this is a min-heap PQ, the highest priority is the lowest 64-bit integer
@@ -65,9 +79,12 @@ global_request_scheduler_minheap_initialize()
 {
 	priority_queue_initialize(&global_request_scheduler_minheap, sandbox_request_get_priority_fn);
 
-	struct global_request_scheduler_config config = { .add_fn    = global_request_scheduler_minheap_add,
+	struct global_request_scheduler_config config = {
+		.add_fn               = global_request_scheduler_minheap_add,
 		.remove_fn            = global_request_scheduler_minheap_remove,
-		                                          .peek_fn   = global_request_scheduler_minheap_peek };
+		.remove_if_earlier_fn = global_request_scheduler_minheap_remove_if_earlier,
+		.peek_fn              = global_request_scheduler_minheap_peek
+	};
 
 	global_request_scheduler_initialize(&config);
 }

runtime/src/local_runqueue_minheap.c

@@ -142,10 +142,17 @@ local_runqueue_minheap_preempt(ucontext_t *user_context)
 		         current_sandbox->request_arrival_timestamp, local_deadline, global_deadline);
 #endif
 
-		int return_code = global_request_scheduler_remove(&sandbox_request);
+		int return_code = global_request_scheduler_remove_if_earlier(&sandbox_request, local_deadline);
 
 		/* If we were unable to get a sandbox_request, exit */
-		if (return_code != 0) goto done;
+		if (return_code != 0) {
+#ifdef LOG_PREEMPTION
+			debuglog("Preemption aborted. Another thread took the request\n");
+#endif
+			goto done;
+		}
+
+		assert(sandbox_request->absolute_deadline < local_deadline);
 
 #ifdef LOG_PREEMPTION
 		debuglog("Preempted %lu for %lu\n", local_deadline, sandbox_request->absolute_deadline);

runtime/src/priority_queue.c

@@ -244,6 +244,18 @@ priority_queue_delete(struct priority_queue *self, void *value)
  */
 int
 priority_queue_dequeue(struct priority_queue *self, void **dequeued_element)
+{
+	return priority_queue_dequeue_if_earlier(self, dequeued_element, UINT64_MAX);
+}
+
+/**
+ * @param self - the priority queue we want to add to
+ * @param dequeued_element a pointer to set to the dequeued element
+ * @param target_deadline the deadline that the request must be earlier than in order to dequeue
+ * @returns RC 0 if successfully set dequeued_element, -ENOENT if empty or if none meet target_deadline
+ */
+int
+priority_queue_dequeue_if_earlier(struct priority_queue *self, void **dequeued_element, uint64_t target_deadline)
 {
 	assert(self != NULL);
 	assert(dequeued_element != NULL);
@@ -253,7 +265,8 @@ priority_queue_dequeue(struct priority_queue *self, void **dequeued_element)
 
 	LOCK_LOCK(&self->lock);
 
-	if (priority_queue_is_empty_locked(self)) goto err_enoent;
+	/* If the dequeue is not higher priority (earlier timestamp) than targed_deadline, return immediately */
+	if (priority_queue_is_empty_locked(self) || self->highest_priority >= target_deadline) goto err_enoent;
 
 	*dequeued_element             = self->items[1];
 	self->items[1]                = self->items[--self->first_free];