Why when I add mxDestroyArray(myArray) to my code MATLAB crashes?

Dear All,

I have a problem with using mxDestroyArray. When I add it to my code, MATLAB crashes. Shouldn't I destroy any mxArray that I declared in my code just to avoid memory leak? Shouldn't each mxArray *myArr correspond to a mxDestroyArray(myArr) when the array is no longer needed?

Thanks,

Ahmd

[James Tursa]

Please post the offending code (or a small subset of it that reproduces the problem) so we can comment on it.

Answer 1

[Kaustubha Govind]

You should only call mxDestroyArray on locally created mxArrays that are not being returned in plhs. Are you deleting mxArrays that are present in either prhs or plhs?

[AP]

This is exactly what I do. Actually, I don't delete mxArrays returned by plhs. I only delete locally created ones.

[Kaustubha Govind]

Okay. In that case, I would second James Tursa's suggestion to post the offending code.

Answer 2

[Andrew Stamps]

Does your mxArray happen to contain a Java object? I recently discovered the hard way that calling mxDestroyArray() on an mxArray that contains a Java object will cause a crash, even if you otherwise should call mxDestroyArray().

If you clear the pointer to the Java object before calling mxDestroyArray(), then it doesn't seem to crash, although I don't know if there are other ramifications.

e.g.:

mxSetData(myArr, NULL);
mxDestroyArray(myArr);

[James Tursa]

Can you post an example of an mxArray that contains a Java object that causes a crash?

[Andrew Stamps]

I encountered this when calling a C shared library generated by the MATLAB Compiler, so maybe this doesn't apply to mex functions as well, but here's a sample function where the error occurs:

static long getNumberOfStreams(const INTEGER instanceHandle)
{
  long iLength;
  mxArray *numStreams = NULL;
  mxArray *streamArray = NULL;

    if (!mlfGetStreams(2, &streamArray, 
        &numStreams, domArray[instanceHandle]))  {
  return 0;
  }
  iLength = (long) *(mxGetPr(numStreams));

   mxDestroyArray(streamArray);  // Why does this cause a crash?
   mxDestroyArray(numStreams);

   return (iLength > 0) ? iLength : 0L;
}

In its intended use, the input array domArray[instanceHandle] is of class org.apache.xerces.dom.DeferredDocumentImpl and is held in global memory. I am not using the first output argument from the function, streamArray, but it should hold an object of class org.apache.xerces.dom.DeepNodeListImpl. The second output argument is a standard scalar double. If I call mxDestroyArray on streamArray without mxSetData(streamArray, NULL) first, then I get a segmentation fault.

Thanks.