Boost thread_group returns empty Matrix (openCV)

Question

I'm trying to use thread_group from the boost libraries to manipulate matrix objects from the openCV libraries (the program is written in C++). However when I try to save the matrices after joining the main thread again, the matrix doesn't contain any data. Can anyone provide an example how to manipulate matrices using boost thread_group ? (I really need multithreading, since the computation takes days otherwise)

Here is the code I'm using so far:

Mat myMatrix;
// Start threads
boost::thread_group threadGroup;
threadGroup.create_thread(boost::bind(&manipulateMatrixFunction,myMatrix));
threadGroup.join_all();

The matrix is only declared in the main thread. The initialisation with number of rows, cols and datatype takes place inside "manipulateMatrixFunction". (Maybe that is part of the problem?)

Answer 1

Pass the Mat instance by reference:

#include <boost/ref.hpp>

//...
threadGroup.create_thread(boost::bind(&manipulateMatrixFunction,boost::ref(myMatrix)));
//...

But make sure that this instance outlives the thread.