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Re: Node lifetime question

From: Joe Berkovitz <joe@noteflight.com>
Date: Tue, 4 Oct 2016 12:25:42 -0400
Message-ID: <CA+ojG-a3aSOK+ZrUfTMbRsHo3RwoJN6p+JYyuiwvOoXhJzMg3Q@mail.gmail.com>
To: Paul Adenot <padenot@mozilla.com>
Cc: Raymond Toy <rtoy@google.com>, Audio Working Group <public-audio@w3.org>
Well, we are trying to establish rules for observability. Perhaps we're
saying, based on the previous example, that the rules are this: a
modulation signal alone, in the absence of an input, is not observable.
That seems fine to me. Would you agree?

.            .       .    .  . ...Joe

Joe Berkovitz
President
Noteflight LLC

+1 978 314 6271

49R Day Street
Somerville MA 02144
USA

"Bring music to life"
www.noteflight.com

On Tue, Oct 4, 2016 at 11:57 AM, Paul Adenot <padenot@mozilla.com> wrote:

> I suppose we could collect everything here. The key is observability.
> Implementors can do anything they feel like as long as the result is not
> observable.
>
> Paul.
>
> On Tue, Oct 4, 2016 at 5:36 PM, Joe Berkovitz <joe@noteflight.com> wrote:
>
>> Sorry, I meant to remove amp from reachability. Updated example:
>>
>>   var mod = new OscillatorNode(...); // modulation source
>>   var sig = new OscillatorNode(...);  // signal source
>>   sig.connect(amp);
>>   var amp = new GainNode();
>>   mod.connect(amp.gain);
>>   amp.connect(ctx.destination);
>>   mod.start();
>>   sig.start();
>>   sig.stop(ctx.currentTime + 1);
>>   sig = null;  // note: mod is still playing, and is also retained by a
>> JS reference
>>   amp = null;
>>
>>
>> .            .       .    .  . ...Joe
>>
>> Joe Berkovitz
>> President
>> Noteflight LLC
>>
>> +1 978 314 6271
>>
>> 49R Day Street
>> Somerville MA 02144
>> USA
>>
>> "Bring music to life"
>> www.noteflight.com
>>
>> On Tue, Oct 4, 2016 at 11:35 AM, Paul Adenot <padenot@mozilla.com> wrote:
>>
>>> In your example, `amp` is till reachable, so it stays alive.
>>>
>>> Paul.
>>>
>>> On Tue, Oct 4, 2016 at 5:32 PM, Joe Berkovitz <joe@noteflight.com>
>>> wrote:
>>>
>>>> I agree with this outcome, but the reasoning still feels murky. It
>>>> seems that you are saying that an active connection from some source to
>>>> some node via an AudioParam doesn't count as an "input reference" to keep
>>>> it alive, but a connection via its input does. Perhaps that's true, but I
>>>> want to make sure.
>>>>
>>>> Let's try this example. In this one, there are three nodes: two
>>>> oscillators and a GainNode. One oscillator is being amplified, the other is
>>>> modulating the gain node. The source oscillator becomes stopped and has no
>>>> JS references, but the modulation oscillator sticks around. Does the
>>>> GainNode stick around too?
>>>>
>>>>   var mod = new OscillatorNode(...); // modulation source
>>>>   var sig = new OscillatorNode(...);  // signal source
>>>>   sig.connect(amp);
>>>>   var amp = new GainNode();
>>>>   mod.connect(amp.gain);
>>>>   amp.connect(ctx.destination);
>>>>   mod.start();
>>>>   sig.start();
>>>>   sig.stop(ctx.currentTime + 1);
>>>>   sig = null;  // note: mod is still playing, and is also retained by a
>>>> JS reference
>>>>
>>>> Question: does the gain node `amp` remain in the graph or can it be
>>>> GCed?
>>>>
>>>>
>>>> .            .       .    .  . ...Joe
>>>>
>>>> Joe Berkovitz
>>>> President
>>>> Noteflight LLC
>>>>
>>>> +1 978 314 6271
>>>>
>>>> 49R Day Street
>>>> Somerville MA 02144
>>>> USA
>>>>
>>>> "Bring music to life"
>>>> www.noteflight.com
>>>>
>>>> On Tue, Oct 4, 2016 at 4:21 AM, Paul Adenot <padenot@mozilla.com>
>>>> wrote:
>>>>
>>>>> Agreed with Raymond here.
>>>>>
>>>>> Paul.
>>>>>
>>>>> On Tue, Oct 4, 2016 at 12:20 AM, Raymond Toy <rtoy@google.com> wrote:
>>>>>
>>>>>> Once oscB has stopped, and because you've dropped all references to
>>>>>> both A and B, does it matter anymore?  Nothing is observable anymore and
>>>>>> you can't make them observable, so it seems to me we don't have to say
>>>>>> anything.  The implementation can do whatever it wants now.
>>>>>>
>>>>>> On Mon, Oct 3, 2016 at 8:04 AM, Joe Berkovitz <joe@noteflight.com>
>>>>>> wrote:
>>>>>>
>>>>>>> But in that case, A and B both have "playing" references as per the
>>>>>>> Lifetime section of the spec, so JS references are irrelevant.
>>>>>>>
>>>>>>> So here is an improved and hopefully more troubling statement of the
>>>>>>> question:
>>>>>>>
>>>>>>> Let's say that osc A is modulating the frequency of osc B, but that
>>>>>>> B reached its stop time (and A has no stop time). Would we keep B alive
>>>>>>> anyway, because retained node A is modulating it, in spite of the fact that
>>>>>>> B can only produce silence?
>>>>>>>
>>>>>>> Example:
>>>>>>>   var oscA = new OscillatorNode(...);
>>>>>>>   var oscB = new OscillatorNode(...);
>>>>>>>   oscA.connect(oscB.frequency);
>>>>>>>   oscB.connect(ctx.destination);
>>>>>>>   oscA.start();
>>>>>>>   oscB.start();
>>>>>>>   oscB.stop(ctx.currentTime + 1);
>>>>>>>   oscA = oscB = null;
>>>>>>>
>>>>>>>
>>>>>>> .            .       .    .  . ...Joe
>>>>>>>
>>>>>>> Joe Berkovitz
>>>>>>> President
>>>>>>> Noteflight LLC
>>>>>>>
>>>>>>> +1 978 314 6271
>>>>>>>
>>>>>>> 49R Day Street
>>>>>>> Somerville MA 02144
>>>>>>> USA
>>>>>>>
>>>>>>> "Bring music to life"
>>>>>>> www.noteflight.com
>>>>>>>
>>>>>>> On Fri, Sep 30, 2016 at 7:18 PM, Raymond Toy <rtoy@google.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> I think it should.  If A and B are both oscillators and A is
>>>>>>>> connected to, say, B.frequency, I expect to hear the modulated B even if A
>>>>>>>> and B have no Javascript references to them.
>>>>>>>>
>>>>>>>> On Fri, Sep 30, 2016 at 1:22 PM, Joe Berkovitz <joe@noteflight.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> I sat down to work on https://github.com/WebAudio/we
>>>>>>>>> b-audio-api/issues/944 and discovered a question.
>>>>>>>>>
>>>>>>>>> So: we already know (I think) that when AudioNode A's output is
>>>>>>>>> connected to AudioNode B's input, then A has a "connection reference" to B.
>>>>>>>>> Thus, if A is retained, B is retained too.
>>>>>>>>>
>>>>>>>>> But what about the case where AudioNode A is connected to an
>>>>>>>>> AudioParam exposed by AudioNode B? Does A keep B alive in this case?
>>>>>>>>>
>>>>>>>>> .            .       .    .  . ...Joe
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
Received on Tuesday, 4 October 2016 16:26:15 UTC

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