W3C home > Mailing lists > Public > public-webrtc@w3.org > May 2015

Re: Attributes! (Re: Proposal: Add RtpSenderInit parameter to addTrack.)

From: Peter Thatcher <pthatcher@google.com>
Date: Fri, 1 May 2015 16:28:56 -0700
Message-ID: <CAJrXDUEXTo-u3g8AUummuf7ygfyuQsgPHv8w=TXm=0EVL=9fig@mail.gmail.com>
To: Jan-Ivar Bruaroey <jib@mozilla.com>
Cc: "Cullen Jennings (fluffy)" <fluffy@cisco.com>, "public-webrtc@w3.org" <public-webrtc@w3.org>
As both an implementor and an application developer (perhaps even more an
application developer), I want the API to be as simple as possible.  And
having to reason about when effects take place across multiple property
assignments doesn't sound fun at all, with magic stuff happening underneath
to keep it atomic is invariably going to lead to surprising behavior that's
hard to reason about.  I prefer to keep it simple with one method.

On Fri, May 1, 2015 at 4:24 PM, Peter Thatcher <pthatcher@google.com> wrote:

>
>
> On Fri, May 1, 2015 at 2:29 PM, Jan-Ivar Bruaroey <jib@mozilla.com> wrote:
>
>>  On 5/1/15 4:00 PM, Peter Thatcher wrote:
>>
>>  I think making all the parameters of RtpParameters into attributes of
>> RtpSender is a terrible idea.  Every time a change to parameters is made,
>> it's basically telling the RtpSender "stop what you're currently sending,
>> and send something different",
>>
>>
>> This wont happen in my model, if you follow what I wrote.
>>
>>    For example, look at the RtpParameters in ORTC:
>>
>>  dictionary RTCRtpParameters {
>>              DOMString                                 muxId = "";
>>              sequence<
>> ​ ​
>> RTCRtpCodecParameters>           codecs;
>>              sequence<RTCRtpHeaderExtensionParameters> headerExtensions;
>>              sequence<RTCRtpEncodingParameters>        encodings;
>>              RTCRtcpParameters                         rtcp;
>> };
>>
>>  ​ If the JS wants to change both the codecs and headerExtensions, it
>> doesn't want to do:
>>
>>   sender.parameters.codecs = newCodecs;
>>  sender.parameters.headerExtensions = newHeaderExtensions;
>>
>>
>> First off, I'm proposing:
>>
>>  sender.codecs = newCodecs;
>>  sender.headerExtensions = newHeaderExtensions;
>>
>> neater.
>>
>>    ​ Because in between those two lines, you'll end up in a weird state
>> where you are sending the new codecs but the old header extensions.
>>
>>
>> No, not in the model I'm proposing. Internally:
>>
>> RtpSender.codecsSetter would set this.codec = arg, and call
>> this._updateNeeded().
>> RtpSender.headxSetter would set this.headx = arg, and call
>> this._updateNeeded().
>>
>> where this._updateNeeded = function() {
>>     this._uNRequested || Promise.resolve(() => (this._uNRequested =
>> false, this._update()));
>>     this._uNRequested = true;
>> };
>>
>> where this._update() = function() {
>>   this._actualCodec = this._codec;
>>   this._actualHeadx = this._headx;
>>  // etc.
>>   this._makeItSo(); // where this._actualCodec and this._actualHeadx
>> matter.
>> };
>>
>
> ​That all seems so much more complex than just one method that means
> "change what I'm sending".
>
>
>
>>
>>
>>     And, worse, what if you setup something invalid on the header
>> extensions, and it throws an exception?  Now you're doing half old and half
>> new.  And as you expand it from 2 different settings like this to 5
>> different things, it gets even more problematic.
>>
>>
>> Provided the JS catches the exception then there is no problem, if it is
>> uncaught then what you get need only be deterministic imho.
>>
>>     But the problems don't end ther​​
>> e, because the ​objects are more than one level deep.  Imagine the JS
>> does this:
>>
>>   var first = sender.parameters.codecs.splice(0, 1);
>>  sender.parameters.codecs.push(first);
>>
>>
>>  ​ Now there's an intermediate state where the codec is missing.  ​
>> ​
>> ​ And what if there were only one codec in the list to begin with?  Does
>> the sender stop sending in the intermediate state?
>>
>>
>> Not a problem in the model above.
>>
>>    And I could come up with a lot more examples.  The point is that
>> there will be intermediate sender states for every little operation the JS
>> does, and reasoning about those states is too complex.  It's much easier to
>> have one atomic operation done via setParameters.​
>>
>>
>> Not a problem in the model above.
>>
>> This is deterministic, and attributes reflect what's been set in the
>> current task for values set in the current task, and actual values for
>> values not set in the current task.
>>
>> A little more work on the implementation, but simpler for the JS writer.
>>
>> .: Jan-Ivar :.
>>
>>
>
Received on Friday, 1 May 2015 23:30:03 UTC

This archive was generated by hypermail 2.3.1 : Monday, 23 October 2017 15:19:44 UTC