Prevent MEX Memory Persistence

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Andrew 2014-9-10

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关闭： MATLAB Answer Bot 2021-8-20

Is there a way to prevent the values of class properties of a MEX from persisting? I understand there are functions to cause memory to persist (i.e. "mexMakeMemoryPersistent"); but I don't see a function like "mex_DONT_MakeMemoryPersistent".

For instance, if I have:

SomeClass.h

. . . . . . . . . . . . . . . .

class CSomeClass {

public: CSomeClass(); ~CSomeClass();

int iVariable;

};

vars.cpp . . . . . . . . . . . . . . . .

#include "SomeClass.h"

CSomeClass oSC;

mains.cpp . . . . . . . . . . . . . . . . #include "SomeClass.h"

extern CSomeClass oSC;

void mexFunction(itype nlhs, mxArray *plhs[], itype nrhs, const mxArray *prhs[]) {

//This will print 0 the 1st time

//This will print 100 the 2nd time

mexPrintf("oSC.iVariable = %d\n", oSC.iVariable);

oSC.iVariable = 100;

}

Now within Matlab:

>>mex mains.cpp SomeClass.cpp

>>mains

oSC.iVariable = 0

>>mains

oSC.iVariable = 100

//This is to demonstrate that the value of oSC.iVariable persisted between MEX calls

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Answer 1

Geoff Hayes 2014-9-12

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Andrew - the way I understand how MEX works (and I could be off) is that by calling the MEX function, you are loading it into memory, and it will remain there until you clear the function or terminate your MATLAB session. You can see this "loaded" function using the inmem function. After calling mains the first time, type the following code in the Command Window

 [loadedFncs,loadedMexFncs] = inmem('-completenames');
 loadedMexFncs
 loadedMexFncs = 
    '/Applications/MATLAB_R2014a.app/toolbox/matlab/graph2d/private/lineseriesmex.mexmaci64'
    '/Users/geoff/Development/matlab/testing/mains.mexmaci64'

So the function is in memory, as is the instance of the CSomeClass class. And when you call mains again, you observe that the iVariable is now 100.

If you want to clear the persistent variable between calls to mains, then you could just clear the function in between the two calls

 >> mains
     oSC.iVariable = 0
 >> clear mains
 >> mains
     oSC.iVariable = 0

Or you could create your instance of CSomeClass in another manner (for example, as a local variable with the mains function) so that it will not persist between calls to mains.