Re: about memory

[Craig Markwardt <craigmnet(at)cow.physics.wisc.edu>]

Amar Nayegandhi <anayegan@csee.usf.edu> writes:

> This is a general question about memory management.
> can i free memory allocated to an array if I have finished using it in
> the program?  suppose 
> arr_a = fltarr(10000,10000)
> if i don't need array arr_a anymore, would
> arr_a = 0
> free the memory used by arr_a?  I would expect it to now utilize only
> 2(or 4) bytes of memory.

The answer to the question is "yes," but also "it depends."  The
answer is "yes" because the memory is indeed made available again to
the same IDL process.  I use 

  A = 0

every day when I am done with a variable.  It's totally legit.  Hong
may need go no further than this, although I agree that he's dealing
with extremely large arrays which might be better suited with a tiled
or chunked approach.

The answer is also "it depends," because it depends on which platform
you are using.  I believe that under Windows the memory is actually
returned to the OS.  Thus, other programs are able to use the memory
again.  Under Unix this is much less likely, so once the memory is
allocated to one session of IDL, it stays there until the session ends
(and is not available to another process).  [ I think this is not
*always* true, but mostly true. ]

Every so often somebody asks, "why is IDL eating all my memory?"  It's
basically unavoidable.  Sorry for this diversion.

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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