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From "Mattmann, Chris A (388J)" <chris.a.mattm...@jpl.nasa.gov>
Subject Re: Webgrid OFSNGetHandler customization
Date Fri, 10 Dec 2010 14:43:21 GMT
Hey Rishi,

> I think my question is whether there exists some specification allowing for processing
of an entire product to occur before bytes of a product are returned. The processing should
occur before the product is returned via "retrieveChunk" and only occur once.  The only way
I can think of enabling this kind of feature to have special code within "retreiveChunk" which
'processes' the product only during the first invocation of 'retrieveChunk', and subsequently
returns the processed bytes in any following invocations. Do you have any recommendations
on a better technique or does the webgrid infrastructure support for something like this?

Yeah, actually one thing you *can* assume is that there will always be a first call to query(XMLQuery
q), even in the case of the LargeProductQueryHandler. So, one thing that I've done in the
past is to realize what the user is asking for on query(XMLQuery q), then cook up some id
to shove into the LargeResult returned as part of XMLQuery.getResults().add(LargeResult...).
That id can then be used (and is actually used later) when retrieveChunk is called. 

So, then you'll know at the query(XMLQuery q) time what the user is going to next ask for
in a series of subsequent calls to retrieveChunk, so in the initial query(XMLQuery q) method,
you may try doing the initial (and 1-time only) processing required for the query *first*,
then cache the result or something that you make available in retrieveChunk next. Of course,
if you cache it you'll have to clean it up after the last retrieveChunk call, but the good
news is, you've got one more method call in there to take care of that (the close(id) method
that's part of the interface). You can take care of the release of resources in that method
and you're good!


Chris Mattmann, Ph.D.
Senior Computer Scientist
NASA Jet Propulsion Laboratory Pasadena, CA 91109 USA
Office: 171-266B, Mailstop: 171-246
Email: chris.a.mattmann@nasa.gov
WWW:   http://sunset.usc.edu/~mattmann/
Adjunct Assistant Professor, Computer Science Department
University of Southern California, Los Angeles, CA 90089 USA

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