MATLAB: How to make memory persistent between calls to a MEX-file in MATLAB

MATLABmemorymexmexmakearraypersistentmexmakememorypersistentpersistent

I would like to know if memory allocated with mxCalloc remains persistent between calls to a MEX-file.

Best Answer

By default, in a MEX-file, mxCalloc generates non-persistent mxCalloc data. In other words, the memory management facility automatically de-allocates the memory as soon as the MEX-file ends. If you want the memory to persist after the MEX-file completes, call mexMakeMemoryPersistent after calling mxCalloc. If you write a MEX-file with persistent memory, be sure to register a mexAtExit function to free allocated memory in the event your MEX-file is cleared.
For example:
 // test.c
 #include <stdlib.h>
 #include "mex.h"
 static double *myarray = NULL;
 double *pr;
 void exitFcn() {
   if (myarray != NULL)
 mxFree(myarray);
 }
 void mexFunction(int nlhs,mxArray *plhs[],int nrhs, const mxArray *prhs[])
 {
   if (nrhs<1 | mxIsChar(prhs[0]))
 mexErrMsgTxt("Must have one non-string input");
   if (myarray==NULL) {  
 /* since myarray is initialized to NULL, we know
       this is the first call of the MEX-function 
   after it was loaded.  Therefore, we should
   set up myarray and the exit function. */
 /* Allocate array. Use mexMackMemoryPersistent to make the allocated memory persistent in subsequent calls*/
 mexPrintf("First call to MEX-file\n");
         myarray = mxCalloc(1,8);
         mexMakeMemoryPersistent(myarray);
         mexAtExit(exitFcn);
   }
   mexPrintf("Old string was '%f'.\n",myarray[0]);
   pr = mxGetPr(prhs[0]);
   mexPrintf("New string is '%f'.\n",pr[0]);
   memcpy((char*)myarray,(char*)mxGetPr(prhs[0]), sizeof(double));
 }
You can compile this MEX-file with the following command:
mex test.c
To run the MEX-file, pass in a single number. For example:
test(3)
Repetitive calls to the test MEX-file will show that the previous input is stored between calls. To clear the MEX-file from memory, use the command:
clear mex
For more information on persistent variables in MEX-files, refer to the relevent documentation by entering the following at the MATLAB prompt:
doc mexMakeArrayPersistent
and
doc mexMakeMemoryPersistent
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