Memory leak with web audio api oscillator

问题:

http://codepen.io/superuntitled/pen/EjZOjw/?editors=001

I have a little web instrument (see link above) that has a memory leak, and I am unsure how to plug it.

The following function is called when an element is hovered over (there are a couple hundred of these).

function tone(id, freq, tonelength) {

  gainNodes.id = audioCtx.createGain();
  osc.id = audioCtx.createOscillator();
  osc.id.connect(gainNodes.id);
  // set frequency and gain
  osc.id.frequency.value = freq;
  osc.id.start(0);

  gainNodes.id.connect(audioCtx.destination);

  gainNodes.id.gain.linearRampToValueAtTime(.1, audioCtx.currentTime);

  gainNodes.id.gain.linearRampToValueAtTime(0, audioCtx.currentTime + parseFloat(tonelength));

}

I think that duplicate oscillators are being created, but am not sure how to check if this is the case, or how to avoid it.

I have a feeling I should check to see if the oscillator already exists, and just run the gain, but I am not sure how to do that.

I have tried to stop the oscillator after it's duration, but this does not seem to stop the leak: http://codepen.io/superuntitled/pen/rVmqYX?editors=001

osc.id.stop(audioCtx.currentTime + parseFloat(tonelength));

Any thoughts on how this could be done?

回答1:

The thing with osc.id is a little weird, since you're setting id as a property name instead of osc[ id ] – but leaving that part aside, you'd want to add this to the bottom of your tone() function:

var current = osc.id;

current.stop( audioCtx.currentTime + 2 );

current.onended = function() {
  current.disconnect();
};

That basically says "Stop playing after 2 seconds, and when you're done, disconnect yourself from the AudioContext".

If id was dynamically assigned to osc (e.g. osc[ id ]), then you'd likely also need to delete osc[ id ] – but that seems to just be getting overridden each time tone() is called with the way you have it now – so the old oscillator should become eligible for garbage collection.

The reason for the current variable is that by the time onended fires, osc.id will likely have been reassigned – so you need a reference to the original oscillator.

Hope that helps.