Reducing memory by emulating IDL's temporary() function

[Judd Storrs]

Hello,

I previously posted to octave-help about IDL's temporary() function which can be used in IDL to reduce memory duplications in some situations. The documentation for IDL's function can be found at http://idlastro.gsfc.nasa.gov/idl_html_help/TEMPORARY.html

From the summary:

"The TEMPORARY function returns a temporary copy of a variable, and sets
the original variable to "undefined". This function can be used to
conserve memory when performing operations on large arrays, as it
avoids making a new copy of results that are only temporary. In
general, the TEMPORARY routine can be used to advantage whenever a
variable containing an array on the left hand side of an assignment
statement is also referenced on the right hand side."

I've cobbled together a DLM that tries to replicate this behavior in octave (code at bottom of message). Here's the code I'm using for testing it:

% Baseline
A = zeros(4096,4096);
B = zeros(4096,4096);
A = A + B + B;

% Using temporary()
A = zeros(4096,4096);
B = zeros(4096,4096);
A = temporary("A") + B + B;

Right now, temporary() takes a string, because I haven't figured out how to find the symbol_record of the parameter.

I think it may be working -- I used the gnome-system-monitor graphs and increased the matrix sizes until I could see the bumps in the graphs. Using the baseline code I think I see the memory use step up three times. Using temporary it only steps up twice. Is there a better way to monitor octave's memory use?

--judd


temporary.cc:

#include <oct.h>

extern OCTINTERP_API symbol_table *curr_caller_sym_tab;

DEFUN_DLD(temporary, args, ,
          "Try to remove a variable from the caller scope and also return it.")

{
  std::string name = args(0).string_value();
  symbol_record * ptr;
  ptr = curr_caller_sym_tab->lookup(name);
  octave_value retval = ptr->def();
  ptr->clear();
  return retval;
}