Variable of same instance has different values depending on where it's accessed from?

Development
1

I am working on a MIDI effect plugin in I have a variable which appears to have a different value depending on the class it’s accessed from. To hopefully make things more clear, here’s a rough outline of the relevant code structure.

class AudioProcessor
{
    ScaleTuning scaleTuning;

    void processBlock(); // calls scaleTuning.processMidi()
}

class AudioProcessorEditor
{
    ScaleTuningEditor scaleTuningEditor;
    AudioProcessor audioProcessor; // reference to instance of AudioProcessor
}

class ScaleTuning {
    int key;
    void processMidi();
    int getKey(); // returns key
}

class ScaleTuningEditor
{
    ScaleTuning scaleTuning; // reference to audioProcessor's scaleTuning
    void update(); // called every 30ms by audioProcessorEditor instance
}

If I use getKey from a method called by processBlock (audio thread) it returns the expected value. However, if I call getKey from update (gui thread), it returns a the same value regardless of what key appears to be when called from processBlock.

There is one exception: getKey() returns the right value in update if it’s the first time it’s called after the plugin GUI is opened.

Any idea what’s going on? Is there anything I can do to make this question more clear? I’m fairly new to C++, so I may be making a straightforward noob mistake.

Thank you!

2

Try

class ScaleTuningEditor
{
    ScaleTuning& scaleTuning; // reference to audioProcessor's scaleTuning
    void update(); // called every 30ms by audioProcessorEditor instance
}

Rail

3

If you access key from different threads, you should make it atomic. Otherwise the compiler is free to potentially optimize that stuff away.

4

Yep, it was this! Thank you for catching this, and apologies for the basic mistake!