DLD files and memory allocation

[Fredrik Lingvall]

Hi,

I am working on a few  MEX/DLD functions for performing in-place 
operation on
(large) matrices for SMP-machines. The simplest one is just for copying 
data from
one matrix to another using several threads in parallel.

I'm doing this by changing the contents of pre-allocated matrices to avoid
the overhead of (temporary) allocating new memory. Using Matlab this 
works fine, but
in Octave the address of the input parameters seems to change when I 
call the copy function
several times. Furthermore, altering the contents of an input parameter 
has no effect.

An example (I do a printf("A = %p B = %p\n",A,B); inside the mex-function)

1) Matlab:
>> n_threads = 1;
>> A = zeros(5,5);
>> B = randn(5,5);
>> copy_p(A,[1 5],[1 5],B,n_threads);
A = 0xb53e4a70 B = 0xb53e4c30
>> copy_p(A,[1 5],[1 5],B,n_threads);
A = 0xb53e4a70 B = 0xb53e4c30
>> copy_p(A,[1 5],[1 5],B,n_threads);
A = 0xb53e4a70 B = 0xb53e4c30
>> copy_p(A,[1 5],[1 5],B,n_threads);
A = 0xb53e4a70 B = 0xb53e4c30

The adress of A and B do not change between calls.

2) Octave (2.1.71):

octave:18> n_threads = 1;
octave:19> A = zeros(5,5);
octave:20> B = randn(5,5);
octave:21> copy_p(A,[1 5],[1 5],B,n_threads);
A = 0x8b31cf0 B = 0x8b31f40
octave:22> copy_p(A,[1 5],[1 5],B,n_threads);
A = 0x8b31cf0 B = 0x8b31780
octave:23> copy_p(A,[1 5],[1 5],B,n_threads);
A = 0x8b317d8 B = 0x8b32060
octave:24> copy_p(A,[1 5],[1 5],B,n_threads);
A = 0x8b316d8 B = 0x8b32018

Here A and B gets a new adress each time I call the function. Does this
mean that Octave make copies of all input parameters? Not good
if A and B is large.

I'm using the octave-forge mex-tools for building the oct-files.

/Fredrik




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