sys/event/thread: optimize stack usage

Author: derMihai

sys/event/thread.c

@@ -31,17 +31,16 @@ struct event_queue_and_size {
     size_t q_numof;
 };
 
-static void *_handler_thread(void *tagged_ptr)
+/* ARM GCC ignores that this function has no exit path, hence NORETURN. */
+NORETURN static void *_handler_thread(void *tagged_ptr)
 {
     event_queue_t *qs = ptrtag_ptr(tagged_ptr);
     /* number of queues is encoded in lower pointer bits */
     size_t n = ptrtag_tag(tagged_ptr) + 1;
     event_queues_claim(qs, n);
     /* start event loop */
     event_loop_multi(qs, n);
-
-    /* should be never reached */
-    return NULL;
+    UNREACHABLE();
 }
 
 void event_thread_init_multi(event_queue_t *queues, size_t queues_numof,

sys/include/event.h

@@ -416,7 +416,8 @@ event_t *event_wait_timeout_ztimer(event_queue_t *queue,
  * It is pretty much defined as:
  *
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~ {.c}
- *     while ((event = event_wait_multi(queues, n_queues))) {
+ *     while (1) {
+ *         event_t *event = event_wait_multi(queues, n_queues);
  *         event->handler(event);
  *     }
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -434,9 +435,8 @@ event_t *event_wait_timeout_ztimer(event_queue_t *queue,
  */
 static inline void event_loop_multi(event_queue_t *queues, size_t n_queues)
 {
-    event_t *event;
-
-    while ((event = event_wait_multi(queues, n_queues))) {
+    while (1) {
+        event_t *event = event_wait_multi(queues, n_queues);
         if (IS_USED(MODULE_EVENT_LOOP_DEBUG)) {
             uint32_t now;
             ztimer_acquire(ZTIMER_USEC);