thread::yield_now() does not yield about esp-idf-sys

[ivmarkov]

After browsing the ESP-IDF documentation myself, I'm not really sure that this is a bug :) . A few notes:

• How do you know that it does not yield? The fact that you get the WDT triggered is not an indication that it does not yield, because the default WDT is watching the idle tasks, not your main task, nor the extra task you spawn here as a separate thread
• ESP-IDF uses pre-emptive execution. Meaning, if a higher priority task is ready, the lower priority task will be preempted.
• Idle tasks on ESP-IDF run with priority 0, the main task (and I suspect - also the extra one you create) runs with priority 1 (check table "List of Tasks Created During Startup" here) so what most likely happens is that the thread does yield, maybe even the idle task for that core is scheduled, but then it gets almost immediately preempted by the main task or the thread task you are spawning, and as a result the watchdog does trigger. This also explains why it does work with a higher sleep delay in #66

Last but not least, the fact that you can reproduce all of these with plain vTaskDelay() calls as well means that the problem is not really in Rust STD, but is a basic behavior of ESP-IDF itself. And as per above, I doubt that this behavior is a bug.

[andresv]

Excellent point. I will close it.