I call a mex function and do some operations with its results and then matlab crashes

Question

Maider Marin 2012-1-13

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https://ww2.mathworks.cn/matlabcentral/answers/25998-i-call-a-mex-function-and-do-some-operations-with-its-results-and-then-matlab-crashes

I create a mex function to use a subroutine I code in C++. I compiled without errors. Then run an example have a correct answer, then modify the answer, create a figure with the answer seconds after it Matlab crashes. Here is the code:

row=145;col=145;  
nn=row*col
i = 1;  b1=b((i-1)*nn+1:i*nn);
[sol,iter,relres1]= BiCGStabNineDiag(Diag,DiagLU,b1,row,tol,maxit); %mexFunction
sol=reshape(sol,row,col);
figure,imshow(sol,[])

There is a message from windows saying that there is an error and it has to close matlab. After it I found a log file. describing problems with Java y netdll.dll

#
# An unexpected error has been detected by Java Runtime Environment:
#
#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x0000000077aeec75, pid=3636, tid=2068
#
# Java VM: Java HotSpot(TM) 64-Bit Server VM (11.2-b01 mixed mode windows-amd64)
# Problematic frame:
# C  [ntdll.dll+0x4ec75]
#
# If you would like to submit a bug report, please visit:
#   http://java.sun.com/webapps/bugreport/crash.jsp

After that there is a lenghty description of the thread and registers, etc. I am checking my mexFunction but the answers are correct and since it changes the vector sol to a matrix and then shows its image I thought it does not have to do with my mex function. But before this mablab never crashed then I suspect it has something to do with destroying the output. I used this at the end of my mexFunction

    mxDestroyArray(plhs[0]);
    mxDestroyArray(plhs[1]);
    mxDestroyArray(plhs[2]);

but I got the same results. I would appreciate any help.

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Answer 1

James Tursa 2012-1-13

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You should never use mxDestroyArray on any of the plhs[*] values ... that will guarantee a MATLAB crash since MATLAB will attempt to use invalid memory downstream. I would hazard a guess that you may have other problems in your mex code as well, so I would suggest posting it.

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Maider Marin 2012-1-13

thanks, very much. I used mxDestroyArray out of desperation. But I suppose you are right since matlab behave the same without the mxDestroyArray lines. The function with everything (structs, sub-routines, main function and mex) is about 560 lines. I will try to put the essentials.

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