Strange read violation on parameter change

Audio Plugins
1

I am developing a plugin that relies on loading different IRs when it detects a parameter change. It works fine on FL Studio and a few other DAWs, but in Mixcraft it reliably crashes when the parameter is changed.

I’ve set my Editor class to inherit privately from AudioProcessorValueTreeState::Listener, and added the following to its constructor:

  // ADD ALL PARAM LISTENERS
  apvts.addParameterListener("lb_freq", this);
  apvts.addParameterListener("lb_amt", this);
  apvts.addParameterListener("lc_freq", this);
  apvts.addParameterListener("lc_amt", this);
  apvts.addParameterListener("hb_amt", this);
  apvts.addParameterListener("hb_freq", this);
  apvts.addParameterListener("hc_amt", this);
  apvts.addParameterListener("hc_freq", this);
  apvts.addParameterListener("oversample", this);

Then, I added a private function void parameterChanged(const juce::String& parameterID, float newValue) override to the Editor class.

But in Mixcraft, turning the parameter knob gives me the following exception: Access violation reading location 0xFFFFFFFFFFFFFFFF.

I’ve commented out the entire body of my parameterChanged() function, except for suspending and un-suspending audio processing, and I get the same exception, indicating it was not anything in that function that caused the issue. I added breakpoints at the beginning and end of my parameterChanged() function, and it seems like it executes fine, and that the crash happens somewhere in JUCE’s code after my parameterChanged() function is finished. My call stack is shown below:

image
image910×302 11.6 KB

Here is the JUCE code where the exception occurs, in the AudioProcessorValueTreeState::ParameterAdapter class:

   void parameterValueChanged (int, float) override
    {
        const auto newValue = denormalise (parameter.getValue());

        if (unnormalisedValue == newValue && ! listenersNeedCalling)
            return;

        unnormalisedValue = newValue;

        // The below call is where it crashes
        listeners.call ([this] (Listener& l) { l.parameterChanged (parameter.paramID, unnormalisedValue); }); 
        listenersNeedCalling = false;
        needsUpdate = true;
    }

The disassembly shows the exception happening on almost the last instruction of that line: call qword ptr [rax+8] , and the “registers” window shows RAX = DDDDDDDDDDDDDDDD. So I’m guessing it’s trying to call parameterChanged() on a listener that doesn’t exist?

I’m not sure if this is an issue with JUCE, or if I set up the Editor as a listener in the wrong way. I am using 64-bit Windows 11, JUCE v7.0.2. Does anyone have any ideas on what might be going wrong or how I could fix it?

Thanks so much in advance!

Midi generator plugin: I'm distributing a VST3i, could I distribute a VST3 'Midi Effect' too (for Ableton, Cubase, FL Studio)?
2

Do you remove yourself from the parameter listeners when the editor is destroyed?
Chances are the host creates the editor multiple times, and the destroyed ones are still in the ListenerList causing it to crash…

Just one of many possible explanations

3

Do you have the equivalent removeParameterListener calls in your destructor?

Is Mixcraft creating only one instance of the editor or doing something unexpected?

Rail

4

That was the issue! I added removeParameterListener() calls to the editor’s destructor and the problem is fixed. I didn’t realize I had to remove them myself, although it makes sense now that I think about it. I wasn’t accounting for some DAWs creating an editor multiple times.

Thanks so much for your help! This has been an issue for me for a while, so I really appreciate it.

1 Like