Set processor affinity for MATLAB engine (Windows 7)

Question

I\'m developing an application in c++. One of the components of the application uses Matlab (via the Matlab engine) for data processing. At the same time, a data acquisition

Answer 1

Below is an implementation of the MEX function that @Praetorian described (shows how to use the SetProcessAffinityMask function):

set_affinity.c

#include "mex.h"
#include 

void mexFunction(int nlhs, mxArray* plhs[], int nrhs, const mxArray* prhs[])
{
    HANDLE hProc;
    DWORD_PTR dwAffinityMask;
    unsigned int numCores;

    // check arguments
    if (nlhs > 0 || nrhs != 1) {
        mexErrMsgIdAndTxt("mex:error", "Wrong number of arguments.");
    }
    if (!mxIsDouble(prhs[0]) || mxGetNumberOfElements(prhs[0])!=1) {
        mexErrMsgIdAndTxt("mex:error", "Expecting a scalar number.");
    }

    // number of logical processors
    numCores = (unsigned int) mxGetScalar(prhs[0]);

    // set affinity of current process to use all cores
    hProc = GetCurrentProcess();
    dwAffinityMask = (1 << numCores) - 1;
    if (!SetProcessAffinityMask(hProc, dwAffinityMask)) {
        mexErrMsgIdAndTxt("mex:error", "WinAPI error code: %lu", GetLastError());
    }
}

Example:

On my quad-core hyper-threaded machine, I would invoke the MEX-function as following to allow MATLAB to execute on all 8 logical processors:

>> getenv('NUMBER_OF_PROCESSORS')
ans =
8

>> mex -largeArrayDims set_affinity.c
>> set_affinity(8)

To use only half the number of processors:

>> set_affinity(4)

---

Note the following remark in the MSDN doc page:

Process affinity is inherited by any child process or newly instantiated local process.

Do not call SetProcessAffinityMask in a DLL that may be called by processes other than your own.

So messing with the affinity will affect all computations initiated by MATLAB and its dependent libraries. Here is a post by Raymond Chen on the topic.