I may be off base, but I think this technique would be ineffective
since the server process would be kept busy with an open connection to
the browser. Eventually you'll run out of processes what with all the
clients that end up waiting for something to happen. HTTP is a pull
protocol. :)
The best that I can think of is some sort of queue system (like a
message queue?) would be more appropriate to allow the browser to poll
the server periodically to see if the info is available. Once the info
becomes available, then the server can send it to the browser.
Thousands of light requests are better than hundreds of heavy ones.
But it seems to me that you're leaning towards some daemon that runs
in the background on the server, generating long-running responses to
requests that come from the server. This is close to what you
described with request A and B, but I'd have the actual request
handled by another daemon.
I can get into further detail and speculation, but maybe we'll leave
that as homework.
--Joel
On Nov 12, 2009, at 1:53 PM, Nicolas George wrote:
Hi.
There is an increasingly popular technique to emulate server-
initiated push
over HTTP. I'm sure everyone here knows it well, but for the sake of
completeness: the clients sends a XMLHttpRequest to the server in the
background; the server does not answer it immediately, but keeps it
for
later when there is actually something to say to the client; if the
request
timeouts, the client re-sends it.
I am wondering if this technique is usable with Apache in general and
mod_perl in particular.
The obvious solution is to have the request handler sleep until it has
something to answer does not work, since it requires a worker thread
and a
perl interpreter for each waiting client, and perl interpreters are
few and
expensive.
The ideal solution would be if some part of the request handler
could put
the current request (A) "on hold". Later, the handler for another
request
(B) could retrieve the request A and generate an answer for it, or
at least
wake it up.
Is something like this possible with Apache and mod_perl?
Regards,
--
Nicolas George
