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Re: Passing arrays to MathLink without extra memory allocation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98791] Re: Passing arrays to MathLink without extra memory allocation
  • From: axnavaei at googlemail.com
  • Date: Sun, 19 Apr 2009 04:54:48 -0400 (EDT)
  • References: <gs9ek8$mso$1@smc.vnet.net> <gsbvus$5ka$1@smc.vnet.net>

Hi,

Are there any other solutions for passing pointers to big data from
mathematica to external programs? In this context, an 'external
program' does not need to be a separate process, it could simply be a
loadable shared library. The way matlab deals with its c-extensions is
a good example of what I mean by this.

It seems like those official mathematica functions implemented in
native code do not have the above constraint and it is possible to
pass pointers without deep copying, is this correct? If so, how is it
possible to implement a function like this?

On 18 Apr, 08:37, Jens-Peer Kuska <ku... at informatik.uni-leipzig.de>
wrote:
> Hi,
>
> a) MathLink is always buffered and
> b) it must copy the data into a memory area
>     that bot programs can access
> c) your C-program can never access the memory space
>    of an other program/process. The operating system is
>    responsible to hinder/prevent such operations
>
> Regards
>    Jens
>
> axnav... at googlemail.com wrote:
> > Hi,
>
> > When passing a list/array from mathematica to c using mathlink, eg
> > when calling MLReleaseInteger32List(), it seems mathlink allocates
> > some memory which later has to be freed, eg using
> > MLReleaseInteger32List(). The question is, how is it possible to pass
> > a list from mathematica to c without this c memory allocation?
>
> > This example helps to make the question more clear: Assume MyFunction
> > [BigList] to be a function implemented in c using mathlink, where
> > BigList is a list of integers. Since BigList has been already created
> > in mathematica and its corresponding memory has been allocated, we do
> > not wish to allocate memory once again in c. It looks like one option
> > is to pass BigList by reference, that is:
>
> > SetProperties[MyFunction, HoldAll]
>
> > In this case, does mathlink still allocate memory and copy BigList in
> > the c side?



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