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

Asked by AP on 24 Oct 2012

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

1 Comment

James Tursa on 24 Oct 2012

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

AP

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2 Answers

Answer by Kaustubha Govind on 24 Oct 2012

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?

2 Comments

AP on 24 Oct 2012

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

Kaustubha Govind on 25 Oct 2012

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

Kaustubha Govind
Answer by Andrew Stamps on 15 Feb 2013

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);

2 Comments

James Tursa on 15 Feb 2013

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

Andrew Stamps on 16 Feb 2013

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.

Andrew Stamps

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