InplaceArray: a semi-pointer package for Matlab

Manipulate (multi-dimensional) arrays in the in-place form

Description

This package helps to create "children" arrays that share the same data as the mother array. The children array can be shaped any customized size for later manipulation.

In short it provides some sort of equivalent C-"pointer" where Matlab lacks.

Extreme cautious when using this package, otherwise encountered crashes and memory leaks warranty. For "advanced" users only.

SPARSE, STRUCTURE are currently not supported

ATTENTION: Serious bug in testinplace.m in the first submission. Before the new fixed version is submitted please do not run this function (the rest is OK)

• Acknowledgements: This submission has inspired the following:; sharedmatrix
• MATLAB release: MATLAB 7.8 (R2009a)
• Other requirements: mex setup Tested on 2006B-2009B

[Christophe Lauwerys]

Nice, however, very tricky.
For instance PACK messes up the reference and I have the feeling more things can go wrong when you use memory-related function calls, or am I being too pessimistic?

>> A=1
>> B=inPlaceArray(A);
>> B=2;
>> pack
>> A
A =
  2.1220e-314
>>

[Bruno Luong]

Hi Christophe,
Thank you for report this. It is expected that PACK would mess up with memory pointers.
Bruno

[Joshua Dillon]

Wow this really is a gem!

Any ideas how to handle sparse matrices? ...nothing in matrix.h sadly.

[Joshua Dillon]

I have figured out how to work with sparse matrices. Contact me if interested.

[Bruno Luong]

There is a compilation issue with 2010B, and I still not able to find a good fix. A workaround is compile by hand the mex files:

% On 32-bit platform
mex inplacecolumnmex.c
mex releaseinplace.c

or on 64-bit platform
mex -largeArrayDims inplacecolumnmex.c
mex -largeArrayDims releaseinplace.c

[Bruno Luong]

Edit: save the following in Internal_mxArray.h before building the mex file:

/*
Internal_mxArray.h
Matlab version: 2010B
*/

typedef struct {
    void *reserved;
    int reserved1[2];
    void *reserved2;
    size_t number_of_dims;
    unsigned int reserved3;
    struct {
        unsigned int flag0 : 1;
        unsigned int flag1 : 1;
        unsigned int flag2 : 1;
        unsigned int flag3 : 1;
        unsigned int flag4 : 1;
        unsigned int flag5 : 1;
        unsigned int flag6 : 1;
        unsigned int flag7 : 1;
        unsigned int flag7a: 1;
        unsigned int flag8 : 1;
        unsigned int flag9 : 1;
        unsigned int flag10 : 1;
        unsigned int flag11 : 4;
        unsigned int flag12 : 8;
        unsigned int flag13 : 8;
    } flags;
    size_t reserved4[2];
    union {
        struct {
            void *pdata;
            void *pimag_data;
            void *reserved5;
            size_t reserved6[3];
        } number_array;
    } data;
} Internal_mxArray;

[Joshua Dillon]

Hi Bruno. I confirm this problem for my sharedmatrix submission. It would seem Mathworks has dropped support for array_access_inlining. Sadly, this is probably the beginning of the end for our hacks. Please let me know if you find a method to automatically reverse engineer future implementations of the mxArray object (and I will do the same). --Cheers, Josh

[Andrew]

Hi Bruno. Can I suggest adding the line:

((Internal_mxArray*)(BMAT))->reserved3 = 1; /*give it a reference count*/

Around about line 194 of inplacearray.c. This will tell Matlab not to try to free the memory pointer so:

A = eye(3);
B = inplacecolumn(A, 2);
clear B;

will not cause Matlab to crash (R2009A anyway)
--Cheers, Andrew

[Binlin Wu]

Josh, thank you for your emails. The code is working now for vectors. It's not critical if it works for scalar or not.

This is a great program and will be very helpful.