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From chago <>
Subject Re: Javascript -> JmsReplyTo(TemporaryDestination) -> JSONP
Date Wed, 05 Sep 2007 03:34:02 GMT

northshorefiend wrote:
> Say you have a widget on a webpage. The user clicks 'send' and expects a
> 'synchronous' response.

As you probably know, amq.js initiates a long-poll using an AJAX GET
request. All JMS messages come down in this get pipeline, and it is always
on. This means that it is constantly connected to the server. When there is
data available or when a particular timeout value is reached, received data
(if any) is processed and the connection is reestablished. 

The script file also uses an AJAX POST request to execute JMS commands, such
as listen/unlisten to a topic or queue and send a JMS message. These
requests return immediately with no user-friendly data. So the sending of a
JMS message is asynchronous.

I have used a lot of request/response mechanisms and my favorite is DWR. I
looked at DWR 2.0 carefully when it came out, and it uses a long-poll
connection also. However, a method invocation still executes synchronously.
This means that if you use reverse AJAX and issue a remote method call you
have used your two connections and you cannot process any more AJAX requests
until that POST returns.

I haven't written a full-fledged JMS application yet. The simple stock board
updates and chat applications are straight forward, but what about a full
blown business application or game? I envision one topic/queue or hundreds
depending on whether I want to remain modular or monolithic. I worry about
scale of a modular approach. I'm not sure if JMS is the answer when
decoupling is not so important, but I do believe that the amq.js approach to
web-based remoting has the capability to be the lowest latency approach to
the problem in a pure html/javascript world. Of course, AMF3 blows everyone
out of the water.
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