audio: New `LevelDetectorSPL` instance blocks at `getValue()`

[microbit-carlos]

This programme creates a new instance of LevelDetectorSPL from the raw splitter (the same way as done in uBit.audio constructor), and every call to localLevelSPL->getValue() gets stuck. It seems to be yielding, so likely locked at the internal resourceLock.wait():

• codal-core/source/streams/LevelDetectorSPL.cpp#L331

#include "MicroBit.h"

MicroBit uBit;

static LevelDetectorSPL *localLevelSPL = NULL;
const int DEVICE_ID_UNUSED = 50;

int localLevelGetValue() {
    if (localLevelSPL == NULL) {
        localLevelSPL = new LevelDetectorSPL(*(uBit.audio.rawSplitter->createChannel()), 85.0, 65.0, 16.0, 35.0f, DEVICE_ID_UNUSED);
    }
    uBit.serial.send("Before localLevelSPL->getValue()\n");
    int localLevelValue = localLevelSPL->getValue();
    uBit.serial.send("After localLevelSPL->getValue()\n");
    return localLevelValue;
}

int main() {
    uBit.init();

    uBit.messageBus.listen(MICROBIT_ID_BUTTON_A, MICROBIT_BUTTON_EVT_DOWN, [](MicroBitEvent) {
        uBit.serial.send("Button A: ", SYNC_SPINWAIT);
        uBit.serial.printf("%d\n", localLevelGetValue());
    });
    uBit.messageBus.listen(MICROBIT_ID_BUTTON_B, MICROBIT_BUTTON_EVT_DOWN, [](MicroBitEvent) {
        uBit.serial.send("Button B: ", SYNC_SPINWAIT);
        uBit.serial.printf("%d\n", localLevelGetValue());
    });

    while (true) {
        uBit.serial.send("Loop: ", SYNC_SPINWAIT);
        uBit.serial.printf("%d; %d\n",
            (int)uBit.audio.levelSPL->getValue(),
            localLevelGetValue()
        );
        uBit.sleep(200);
    }
}

The main() function infinite loop calls getValue, so do the button handlers, so we can see this output after pressing button A and B, and nothing more is printed. The uBit.serial.send("After localLevelSPL->getValue()") is never reached:

Loop: Before localLevelSPL->getValue()
Button A: Before localLevelSPL->getValue()
Button B: Before localLevelSPL->getValue()

[martinwork]

It works...

If a sleep(100) (didn't try different numbers) is added inside localLevelGetValue() after localLevelSPL is created...

Or if localLevelSPL is created any time before entering printf, in which case calling uBit.audio.levelSPL->GetValue() seems to provide the required pause (it hangs if localLevelGetValue() is the first parameter).

[martinwork]

... Or if localLevelSPL ->upstream.dataWanted(DATASTREAM_WANTED) is called after creation.

LevelDetectorSPL is created with it's DATA_REQUESTED status set in the constructor, but the splitter channel stream is not delivering pullRequests.

If called immediately, getValue() simply waits on the lock, without calling dataWanted to wake the stream, because DATA_REQUESTED is set.

DATA_REQUESTED is cleared only in periodicCallback, and only after the timeout, if sufficient buffers have been delivered and nothing is waiting for a value.

In this state, calling getValue from another fiber will also just wait on the lock.

The default LevelDetectorSPL's periodicCallback is called inside uBit.init(), which changes its channel's isWanted from DONT_CARE to NOT_WANTED and clears the DATA_REQUESTED status.

The initial DATA_REQUESTED status was added here:
lancaster-university/codal-core@dda12d8

The DATA_REQUESTED status and the dataWanted setting are always changed together, and this problem arises because they are out of sync.