Multithreading with opencv and pthreads - c++

Question

I wanted to get video frames from openCV and render it onto a graphics screen with openGL. I got it to work; however, the video drops frames consistently. I believe its because reading the frame and rendering is all on the same thread. Therefore, I implemented multithreading with pthreads but imshow is just a white screen. Also, it seems like the main thread does not run. I implemented a version with conditions and signals, and one with it. Any pointers to what I am doing wrong will be very helpful. Below is my code:
void *updateloop(void *arg)
{
while(1)
{
pthread_mutex_lock(&frameLocker);
while(my_queue.empty())
{
pthread_cond_wait(&condc, &frameLocker);
}
std::cout << "entering update loop" << std::endl;
current_image = my_queue.front();
my_queue.pop();
/*
if(!current_image.empty())
{
std::cout << "rendering to output window" << std::endl;
cv::imshow("Output Window", current_image);
cv::waitKey(30);
}
*/
pthread_mutex_unlock(&frameLocker);
}
}
void *captureloop(void *arg)
{
cv::Mat tempFrame;
while(1)
{
std::cout << "entering capture loop" << std::endl;
cap.read(tempFrame);
pthread_mutex_lock(&frameLocker);
my_queue.push(tempFrame);
pthread_cond_signal(&condc);
pthread_mutex_unlock(&frameLocker);
}
}
int main(int argc, const char * argv[])
{
cap.open(0);
pthread_mutex_init(&frameLocker, NULL);
pthread_t update, webcam;
pthread_cond_init(&condc, NULL);
pthread_cond_init(&condp, NULL);
pthread_create(&update, NULL, updateloop, NULL);
pthread_create(&webcam, NULL, captureloop, NULL);
pthread_join(update, NULL);
pthread_join(webcam, NULL);
cv::Mat tempFrame;
while (1)
{
pthread_mutex_lock(&frameLocker);
std::cout << "in the main thread" << std::endl;
if(current_image.empty()){
printf("recieved empty frame\n");
continue;
}
if(!current_image.empty())
{
std::cout << "rendering to output window" << std::endl;
cv::imshow("Output Window", current_image);
}
cv::waitKey(1);
pthread_mutex_unlock(&frameLocker);
}
return 0;
}