SDK13 app_sched_execute() infinite recursion

RE: SDK13 app_sched_execute() infinite recursion

Hung Bui — Wed, 12 Apr 2017 08:46:27 GMT

Hi Mike,

I agree that the change was only about the order when we update m_queue_start_index.

But the problem lies on the circular buffer we have on scheduling task. If we have a full queued buffer and we move m_queue_start_index forward, we allow a new task to be scheduled (see app_sched_queue_full() ). And when there is a slot available, m_queue_end_index is allowed to increase and buffer new data, overwriting the data that is pending to be executed by event_handler(p_event_data, event_data_size);

So the issue only happens when

Buffer is full
Event happens between m_queue_start_index = next_index(m_queue_start_index); and event_handler(p_event_data, event_data_size);

RE: SDK13 app_sched_execute() infinite recursion

Mike Voytovich — Tue, 11 Apr 2017 17:27:10 GMT

Thanks for the reply Hung! But, I don't quite understand what you mean by "if the event is freed before executing". The line of code: m_queue_start_index = next_index(m_queue_start_index); is not freeing anything; it's just updating the m_queue_start_index, right? So how could updating m_queue_start_index before calling the handler corrupt the event data?

RE: SDK13 app_sched_execute() infinite recursion

Hung Bui — Tue, 11 Apr 2017 12:22:32 GMT

Hi Mike,

The app_sched_execute() was made to be called from inside main loop, not for calling recursively from within the event itself. You can find this in the description:

/**@brief Function for executing all scheduled events.
 *
 * @details This function must be called from within the main loop. It will execute all events
 *          scheduled since the last time it was called.
 */
void app_sched_execute(void);

The information I got from our developer was that we updated the code from SDK v12 to fix a potential bug that if the event is freed before executing, the data comes with that event can be corrupted before it is executed. That's why we swapped the order.

Calling app_sched_execute() from inside an event handler is not recommended.