"JVM is not running" Error When m file is called in thread function

Hi, All. I created a thread function through mexFunction and tried m file in the thread by using mexCallMATLABWithTrap function. However, it did not properly work. I found the error message through the return value of mexCallMATLABWithTrap. It says, "JVM is not running". Why this happens? Does anybody know about this? Is it technically impossible to call m file from the C++ thread function?

As a reference, here is my summarized files.

1. threadtest.cpp

void mexFunction(int nlhs, mxArray *plhs, int nrhs, 
mxArray *prhs[])
{
  HANDLE hThread;
  unsigned threadID; 
  void* pointer;

    hThread = (HANDLE)_beginthreadex( NULL, 0, &MyThreadFunc, pointer, 0, &threadID );
    WaitForSingleObject( hThread, INFINITE );
    // Destroy the thread object.
    CloseHandle( hThread ); 
}
unsigned __stdcall MyThreadFunc(void * pointer)
{
   mexPrintf("I am in thread!!!!\n");

     mxArray *returnvalue = mexCallMATLABWithTrap(0, NULL, 0, NULL, "test");
     if (returnvalue)
     {
        mexPrintf("I am here!!!!!\n");
        mxArray *plhs = mxGetProperty(returnvalue, 0, "message");
        char *buf;
        int   buflen;
        int   status;
        buflen = (mxGetM(plhs) * mxGetN(plhs)) + 1;
        buf = (char*)mxCalloc(buflen, sizeof(char));
        if (buf == NULL)
            mexErrMsgTxt("Not enough heap space to hold converted string.");        
        status = mxGetString(plhs, buf, buflen); 
        if (status == 0)
          mexPrintf("The converted string is \n%s.\n", buf);
        else
          mexErrMsgTxt("Could not convert string data.");        
     }
     _endthreadex( 0 );
     return 0;
  } 
2. test.m

function test()
  for i = 1 : 10
    fprintf('haha!!!!!!!!!!!!!!!!!!!!\n');
  end

Thanks in advance!

Answer 1

[Richard Alcock]

It's fine to create new threads in MEX file, but accessing MATLAB in anyway, including making calls to the MEX API functions, from the spawned thread is not supported.

See http://www.mathworks.com/support/solutions/en/data/1-V3B5T/

[Brian Kim]

I really appreciate your clear answer. I hope the flexible accessing from threads to MATLAB is supported soon.

[Brian Kim]

I really appreciate your clear answer. I hope the flexible accessing from threads to MATLAB is supported soon.

Answer 2

[Jan]

My Matlab 2009a on WinXP-32bit produces a dramatical crash, when I call mexCallMATLAB from different threads.

The article mentioned by Richard is very interesting: You can run a C-thread in parallel, as long as you do not call Matlab API-Functions. But I do not find a documentation about which function should be avoided exactly: mxGetPr? mxCreateDoubleScalar? mxMalloc? mxGetNaN? Multi-threading is fragile and an exact documentation of thread-safe functions would be very helpful.

[Richard Alcock]

@Jan - I read "the MEX API is not thread safe" in the link to mean that none of mx* and mex* functions are thread-safe.

[Jan]

@Richard: and if the mx* functions are inlined by "mex -inline"?

All modern processors used for scientific computing have multiple cores. Matlab should be used for scientific computing. Therefore Matlab needs a thread save API. Let's see the new features of 2011a.

Answer 3

[Walfredo]

Hello Brian, I have the same problem. Most of the time, if I try a second time, whatever mexCallMATLAB called would work. I thought it would be ok, but just know, one of my mexCallMATLAB is always failing.

Answer 4

[weike yin]

????MATLAB engine????????????? ------------------------- You can try to use MATLAB engine, Is't can eval m file in mex spawned thread.