c++ - OpenCV imshow in Boost Threads -

below code tracking module. detector launched , when detects object of interest, creates tracker object track object using camshift on number of frames until detector finds object. code seems work fine when comment out imshow , waitkey in tracker. when call functions, following error when new tracker (apart first one) created:

qmetamethod::invoke: unable invoke methods return values in queued connections qobject::starttimer: qtimer can used threads started qthread 

i don't know if happening within boost or opencv. ideas how can fix problem? there better way go showing user position of object of interest? lot!

main:

#define face_detect_rate 10 tracker *currenttracker;  boost::mutex displayedimagemutex; mat imagetoshow;     // image displayed main thread  void updatedisplayedimage(mat image){     if (displayedimagemutex.try_lock()){        image.copyto(imagetoshow);        displayedimagemutex.unlock()     } }  rect detectorcallback(rect facerect){     // detector object returns face found here     //  tracker supposed track face in next set of frames     tracker tracker(facerect);     tracker.start(&updatedisplayedimage);     currenttracker = &tracker;     currenttracker->join(); }  int main(int argc, char **argv){     videocapture capture(0);     currenttracker = null;      int framecount = 0;      while (true){         mat frame;         capture >> frame;          if (framecount % face_detect_rate == 0){             detector detector;             detector.start(frame, &detectorcallback);         }          if (displayedimagemutex.try_lock()){             if (imagetoshow.data){                 imshow("results", imagetoshow);                 waitkey(1);             }             displayedimagemutex.unlock();         }     } } 

tracker:

class tracker{ private:     boost::thread *trackerthread;      void run(void (*imageupdatefunc)(mat)){         while (true){             try{                 ...                 //do camshift , stuff                  //show results                 //imshow("stream", imagewithface);                 //waitkey(10);                 imageupdatefunc(imagewithface);                 ...                 boost::this_thread::interruption_point();              } catch (const boost::thread::interrupted&){                 break;             }         }     }   public:     tracker(rect facerect){         ...     }         void start(void (*imageupdatefunc)(mat)){         trackerthread = new boost::thread(&tracker::run, this, imageupdatefunc);     }      void stop(){         trackerthread->interrupt();     }      void join(){         trackerthread->join();     } };