Re: C->JNI->fast webpage updates?

Daniel Pitts <>
Wed, 06 Feb 2008 09:16:50 -0800
Joe wrote:

I'm serious about the static web page thing. Write a C program to put
data in HTML, write it to disk. Users can fetch it there.

Oh, c'mon ... think web page inside an existing web app ...

You really haven't said why you need any kind of dynamic connection.
Does the data arrive very fast? Is it different for each user? (You
just said "no" to that one, actually.) How long will old data be stored?

Because the data is being fed across from the network. Yes, it arrives
fast and can update very fast. Millisecond updates if need be.

Like I said elsewhere, Java can handle network data too. I think that
Mark's suggestion is to have your c program re-write the HTML every time
something changes, rather than have your web-app re-generate the HTML
every time someone requests it. Although, having worked with such a
system, I can say that it adds complications that probably aren't worth
it depending on the number of pages.

I can think of lots of better things than a straight C lib to Java
connection. One would be to save the data in a database, then fetch
it from there. JSP would be ideal for serving data in this case.

No, the data must come in from an existing network connection, existing
C libraries. I need to get that data into a web page and if the data
changes every 90ms, then the page needs to show those same changes. A
database should not be in the mix here, though there is one elsewhere,
but the incoming data is considered real-time data.

Databases can handle real-time data. Unless a delay of 10ms is
unacceptable, in which case you probably shouldn't use a network in the
first place.

But what you are proposing has lots of funny corners that may not make
for a clean solution. Is the C lib multi-threaded, for example?
There could be a nasty surprise for you if the C lib not very
carefully written for access by multiple threads. Saving the data
elsewhere (in HTML, for example, or to a database) breaks this
dependency (and that's a good thing).

The C libs are fine and deliver data fine. This is a must and this is
how the data arrives into the web server.

I'm not proposing anything, however, I'm thinking an applet is the only
way that will do it. I'm asking to see how others have shown or would
show data rates that come in this quick in a web page, how to update
this part of the page this quickly.

Ah. so perhaps we all misunderstood what you wanted...

When a user connects to your web-app, they download the latest HTML
available. We all assumed you wanted to serve them with the most
up-to-date info at that time, but it sounds like you want their browser
to continuously update without them having to refresh the page. There
are several ways to achieve this, but the techniques involved are
orthogonal to the use of JNI to retrieve data.

One technique in particular is to use cometd (google it), cometd is a
bit like push-based AJAX. The browser has a waiting connection, and
when the server knows there is new information, it sends it "immediately".

The other technique involves having a client application (either applet,
flash, or activex) that will connect to the server using a specific
protocol, and listen for the data then.

So, have I understood your problem correctly? There are two ways to
interpret what you've said so far, so please clarify exactly which way
you meant:
a) User gets up-to-date information at request time, but needs to
refresh to get new data.
b) User gets up-to-date information at request time, and it is kept
up-to-date automatically.

Two very different problems that sound similar.

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