Implement a Reading FIFO (source-incompatible)

Overview

There will be a FIFO inside each sensor.

The backend supplies readings to the FIFO. The application pulls items out of the FIFO.

void MyClass::onNewSensorData()
{
    while (sensor->readingsAvailable())
        do_something(sensor->takeReading());
}

Implementation Plan

Remove the reading() method. Add a takeReading() and a readingsAvailable() method.

The readingChanged() signal will be replaced with a newSensorDataAvailable() signal.

The actual FIFO should be a class that's visible to QSensor and to the backend.

Notes

A source-compatible implementation could possibly be done if we use some policy. This would enable the feature to be rolled out to existing users without requiring them to port to a new library. The existing reading method would point to the front of the queue, the queue would replace old with new values and would default to a depth of 1.

Research Questions

Maybe some better method/signal names can be found?

What does example app code look like?

How can we unit test this (should be easy if it's a self-contained class)?

How can we document this (should be mostly private, just document the methods that are exposed in QSensor)?

Does this hold pointers (for polymorphism) or a concrete class (in which case how to we expose per-sensor data)? Should the API be in the sub-classes of QSensor?