| Re: IDL Memory Management [message #18478 is a reply to message #18458] |
Thu, 06 January 2000 00:00  |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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"Myron Brown" <Myron.Brown@jhuapl.edu> writes:
> Hi. I'm having a problem that I'm not sure how to solve. I call a
> procedure I wrote which manipulates large images. When it's done, it passes
> me back a relatively small array. However, AFTER the procedure is complete,
> I have problems with swap space. It appears that something is still
> allocated (or something). I am not using pointers, just simple arrays
> (which I assume get thrown on the stack - maybe not). Any ideas on how to
> deallocate this?
>
This question comes up every so often, and there is no easy answer.
RSI has a "Tip" on its web page which treats this issue in a little
more detail.
I assume you are running under a Unix-type OS. Under Unix the memory
space of any process including IDL is treated as a one-demensional
array of cells. IDL requests more memory from the system on an
as-needed basis. If you do a lot of creating and destroying of IDL
variables, especially with big variables, you can end up with a lot of
unused *HOLES* in memory, and unfortunately holey memory can't be
returned to the system. Windows may or may not be different in this
respect.
The solutions are to:
* avoid making extra copies of your memory hogging image variables.
This includes the implicit copies that are made in arithmetic
expressions.
* read about the TEMPORARY() function, and use it.
* consider some form of "chunking" in your processing. That is,
operate on banded subsets of your image so that your overall memory
footprint is smaller. I do this successfully with gigabytes worth
of data.
Cheers, and good luck,
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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