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Re: What changes to Web Messaging spec are proposed? [Was: Re: Using ArrayBuffer as payload for binary data to/from Web Workers]

From: Jonas Sicking <jonas@sicking.cc>
Date: Wed, 8 Jun 2011 20:33:12 -0700
Message-ID: <BANLkTimTw9F95k6uLybPRtAz7Q98Qq_e7A@mail.gmail.com>
To: Kenneth Russell <kbr@google.com>
Cc: David Levin <levin@chromium.org>, Arthur Barstow <art.barstow@nokia.com>, Andrew Wilson <atwilson@google.com>, Glenn Maynard <glenn@zewt.org>, Dmitry Lomov <dslomov@google.com>, ben turner <bent.mozilla@gmail.com>, "public-webapps@w3.org" <public-webapps@w3.org>, Ian Hickson <ian@hixie.ch>, Travis Leithead <Travis.Leithead@microsoft.com>
On Wed, Jun 8, 2011 at 6:26 PM, Kenneth Russell <kbr@google.com> wrote:
> On Wed, Jun 8, 2011 at 6:14 PM, Jonas Sicking <jonas@sicking.cc> wrote:
>> On Wed, Jun 8, 2011 at 4:27 PM, Kenneth Russell <kbr@google.com> wrote:
>>> On Wed, Jun 8, 2011 at 2:39 PM, David Levin <levin@chromium.org> wrote:
>>>>
>>>>
>>>> On Wed, Jun 8, 2011 at 2:33 PM, Kenneth Russell <kbr@google.com> wrote:
>>>>>
>>>>> I prefer continuing to use an array for several reasons: simpler
>>>>> syntax, better type checking at the Web IDL level, and fewer
>>>>> ECMAScript-specific semantics.
>>>>
>>>> An array makes it harder to do future modifications.
>>>
>>> Possibly, but it makes the design of this modification cleaner.
>>>
>>>> Also with the array, how does "Enhance the ability to pass MessagePorts, so
>>>> that the object graph can refer to them as well" work? Specifically,
>>>> consider an array that contains [arrayBuffer1, port1]. Is port1 something in
>>>> the object graph or a port to be transfer as before?
>>>
>>> In order to maintain backward compatibility, the clone of port1 would
>>> show up in the "ports" attribute of the MessageEvent on the other
>>> side. Additionally, during the structured clone of the object graph,
>>> any references to port1 would be updated to point to the clone of
>>> port1. (The latter is new behavior, and brings MessagePorts in line
>>> with the desired transfer-of-ownership semantics.)
>>>
>>> All other objects in the array (which, as Ian originally proposed,
>>> would implement some interface like "Transferable" for better Web IDL
>>> type checking) would simply indicate objects in the graph to be
>>> transferred rather than copied.
>>
>> This all sounds great to me, but I think we should additionally make
>> the 'ports' attribute on the MessageEvent interface deprecated.
>>
>> The only use case for it is to support existing code which doesn't
>> pass ports in the object graph but rather only in the array in the
>> second argument (i.e. the formerly "ports" argument).
>
> That's not quite correct; as was pointed out earlier in the thread,
> SharedWorkerGlobalScope's onconnect message relies on receiving the
> message port with which to communicate to the outside world in the
> zeroth element of the ports array. See step 7.7.5 in
> http://www.whatwg.org/specs/web-workers/current-work/#shared-workers-and-the-sharedworker-interface
> .
>
> Thinking about this more, that port could be sent as the data
> attribute of the event instead of the empty string. Then the ports
> attribute on MessageEvent could be safely deprecated.

Sounds great to me.

/ Jonas
Received on Thursday, 9 June 2011 03:34:18 GMT

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