Usage of Arduino_Threads requires extension of ArduinoCore-mbed (Danger of CPU hogging)

[aentinger]

In order to avoid CPU hogging by the main thread (loop() of *.ino file) it is necessary to add rtos::ThisThread::yield(); to ArduinoCore-mbed as shown below:

for (;;) {
	loop();
	if (arduino::serialEventRun) arduino::serialEventRun();
+	rtos::ThisThread::yield();
}

For all *.inot defined threads this is automatically done by this code executed after calling the thread's loop() function.

Since this is currently not the case rtos::ThisThread::yield(); is currently called within the main thread of each example (i.e. here) and I think we should rather avoid exposing the raw mbed API to the wider public.

Any side effects you can think of @facchinm?

CC @pnndra @giulcioffi @pennam @MaxPayne86

[facchinm]

I think we should benchmark it on common examples but it shouldn't hurt in a normal execution (since all other threads automatically spawned are either yielding or waiting on semaphores already)

[aentinger]

In the example Threadsafe_Serial_Writer CPU hogging does occur without rtos::ThisThread::yield(), i.e. the output without this statement within ino::loop() is:

[3097] Thread #0: Lorem ipsum ...
[3099] Thread #0: Lorem ipsum ...
[3101] Thread #0: Lorem ipsum ...
[3103] Thread #0: Lorem ipsum ...
[3104] Thread #0: Lorem ipsum ...

but it really should be

[4532] Thread #0: Lorem ipsum ...
[4534] Thread #1: Lorem ipsum ...
[4536] Thread #2: Lorem ipsum ...
[4537] Thread #3: Lorem ipsum ...
[4539] Thread #0: Lorem ipsum ...
[4541] Thread #1: Lorem ipsum ...
[4543] Thread #2: Lorem ipsum ...

True story 😉

[aentinger]

Turned out to be a implementation bug within SerialDispatcher, see #45.