sys/event: No way to stop event queue?!

[carl-tud]

Is there a way to stop an event queue? event_loop(_:) seemingly runs forever. There should be one. If no, why?

[mguetschow]

I've briefly looked into this and I think it turns out to be a bit cumbersome in a general implementation, given that event_loop is implemented under the hood with event_loop_multi, where it wouldn't be as clear what "stopping the event queue" means - just stop listening on one (you'd need more state) or stop listening on all of them?

RIOT/sys/include/event.h

Lines 436 to 439 in 9890215

	static inline void event_loop_multi(event_queue_t *queues, size_t n_queues)
	{
	while (1) {
	event_t *event = event_wait_multi(queues, n_queues);

But given that event_loop is just a static inline which

RIOT/sys/include/event.h

Lines 470 to 476 in 9890215

	* It is pretty much defined as:
	*
	* ~~~~~~~~~~~~~~~~~~~~~~~~~~~ {.c}
	* while ((event = event_wait(queue))) {
	* event->handler(event);
	* }
	* ~~~~~~~~~~~~~~~~~~~~~~~~~~~

you can solve that for your particular use-case along the lines of

static bool _running = false;

static void _start_loop(event_queue_t *queue)
{
    running = true;
    while (_running) {
        event_t *event = event_wait(queue);
        event->handler(event);
    }
}

static void __stop_loop(event_t *ev)
{
    _running = false;
}

static void _stop_loop(event_queue_t *queue)
{
    static event_t ev = { .handler = __stop_loop };
    event_post(queue, &ev);
    event_sync(queue); // if you want to wait until the loop is stopped (from another thread)
    // or just (if only called from within the loop / the same thread)
    // _running = false;
}