On Nov 27, 2005, at 9:03 AM, Dr.Ernie Prabhakar wrote:
On Nov 26, 2005, at 2:42 PM, Kevin Marks wrote:
Ernie, what was the thinking behind adding the delay to AHAH?
A very good question, since I haven't done anything with it yet. :-)
The most important point to note is that the *default* behavior
remains the same:
It turns what was an async on demand call to one that polls at
intervals, but only on success?
That is, you can use the function as today as merely "async on
demand" if you don't specify a delay.
However, my hypothesis is that you can also implement "push" as
"lazy pull."
I'm pretty sure I've seen this hypothesis proven already.
That is, rather than having a separate open socket on the client,
you merely do a non-blocking pull that the server is smart enough
to defer resolving until there's new data, a la:
http://example.com/user/1/messages?lastUpdate=20051128T1800Z
The idea is that the server would hold the request until it had
something new to respond with. I added the delay so that it
wouldn't bury the server with requests in the case where it
(mistakenly) responded immediately.
This originally came up in the context of "pubsub" and "Jabber" --
two protocols that tend to think in terms of "push"; I wanted to
see whether there was a "clean" way to implement them in terms of
HTTP and, specifically, AHAH.
There are scenarios where this can make sense - ie if there are
multiple clients that can update the state of a resource on the
server, and you want a persistent connection open to react to this
quickly.
Yeah, that sort of thing. Basically, any scenario where the client
wants 'instant' notification. The main advantage over polling is
that it requires much less use of network resources. That said, it
does hold a connection on the server, which consumes server
resources. On the other hand, I still suspect the overall impact
is less than if the server had to implement 'true' push (vs. this,
what, "pseudo-push").
There's one little problem with using this in browsers- most (I
think) browsers will constantly look like its loading a page, which
can be quite unsettling to users.
Again, I haven't even tested the code yet to make sure it works,
much less done any detailed studies of its resource impact. If
you're feeling brave, let me know how it works. :-)
-- Ernie P.
-ryan
--
Ryan King
[EMAIL PROTECTED]
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