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MathGroup Archive 2005

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Re: Mathlink memory preservation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56510] Re: [mg56455] Mathlink memory preservation
  • From: Zhengji Li <zhengji.li at gmail.com>
  • Date: Tue, 26 Apr 2005 23:00:19 -0400 (EDT)
  • References: <200504260533.BAA14376@smc.vnet.net>
  • Reply-to: Zhengji Li <zhengji.li at gmail.com>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

  The global variable "image" is allocated in the heap by "new"
operator in "preloadimage",
so I am sure that when calling "filter" "image" should not be NULL.

  By the way, your mathlink program is a stand-alone program and
communicating with Mathematica
via MathLink (over TCP/IP), and it is impossible for Mathematica to
free the memory allocated in it.

On 4/26/05, Bart Janssen <b.j.janssen at tue.nl> wrote:
> Hello,
> 
> I'm writing a C++ mathlink program that should do some image processing.
> 
> The main idea is:
> 1. Load the image into the memory of the mathlink module by
> PreLoadImage[Image__?(MatrixQ[#, NumberQ]&)]
> 2. Obtain a filter response from a filter parameterised by a couple of
> Reals (This way we don't have to send the entire image over the link
> over and over and thus obtain higher evaluation speeds).
> 
> Problem:
> After the preload function is called, the destructor of my image is
> magically called. Because of this the data is not available to the
> filter function.
> 
> Question:
> How can I make sure my data stays in memory?
> (Suggestions on improving the code are welcome too :) )
> 
> Source Code looks like this:
> //-----------------------------------------
> #include <mathlink and other stuff>
> 
> // global variable that holds the image that is processed
> PixelMap<double> *image;
> 
> //
> // Load the image data from mathematica into
> // the global variable image
> //
> void preloadimage(){
>         double* points;
>         long *pdims;
>         long prank;
> 
>         MLGetRealArray(stdlink, &points, &pdims,NULL,&prank);
> 
>         // Remove the old image from memory
>         // Appearantly mathlink does this for me...
> /*      if(image!=NULL)
>                 delete image;
> */
> 
>         image = new PixelMap<double>(pdims[1],pdims[0]);
> 
>         for(int y=0;y<pdims[0];y++)
>                 for(int x=0;x<pdims[1];x++)
>                         image->SetPixel(x,y,points[pdims[1]*y+x]);
> 
> #ifdef DEBUG
>         std::ofstream file ("/home/TUE/bjanssen/debug.txt");
>         file << *image << std::endl;
>         file.close();
> #endif
> 
>        // some junk that for "some" reason has to be here
>         MLNewPacket(stdlink);
>         MLPutInteger(stdlink,1);
> }
> 
> //
> // Return a filter response from a filter
> // applied on global image
> // NOTE: preloadimage has to be called on forehand
> //
> void filter()
> {
> // ... same trickery as above, but then for other arguments
>         double retval = filter(args,image);
> 
>         MLNewPacket(stdlink);
>         MLPutReal(stdlink,retval);
> }
> //-----------------------------------------
> 
> Thanks in advance,
> Kind Regards,
> Bart Janssen
> 
>


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