Getting camera image from thread - c++

Question

I am using opencv library to obtain video from the built-in webcam. The following code works perfectly well when i put camera logic code into the main function, but it doesn't when i put it into separate thread. The task1() thread stops at cv::VideoCapture capture(0). Meanwhile both task2() and the main thread are executing correctly.
Could someone explain me why opencv logic doesn't work when put into separate thread?
My code:
#include <iostream>
#include <string.h>
#include <thread>
#include <unistd.h>
#include <opencv2/opencv.hpp>
using namespace std;
void task1 (){
cout<<"1st thread ";
cv::Mat frame;
cv::VideoCapture capture(0);
if ( capture.isOpened() == false )
{
cout<<"Failed to open camera";
}
cv::namedWindow("Test OpenCV",1);
while ( true ){
capture >> frame;
cv::imshow("Test OpenCV", frame );
int key = cv::waitKey(1);
if ( key == 27 )
break;
}
}
void task2 (){
int n = 0;
while (1){
cout<<"2nd thread "<<n<<"\n";
sleep(3);
n++;
}
}
int main(int argc, const char * argv[]) {
// insert code here...
cout << "Hello, World!\n";
thread t1(task1);
thread t2(task2);
//t1.join();
//t2.join();
int n = 0;
while (1){
cout<<"main thread "<<n<<"\n";
sleep(1);
n++;
}
return 0;
}

Answer 1

Your code runs as it should for me (without any modifications) and I get the live feed through the task1 thread (using OpenCV 2.4.5).
I added -std=gnu++0x flag for compiler support (otherwise g++ throws an error).
g++ -std=gnu++0x opencv_thread.cpp -o opencv_thread `pkg-config --cflags --libs opencv`
Check my console output here. I added a cout << "1st thread "<< endl; within the while loop in task1.
I think the issue might be specific to some opencv versions as I have seen similar issues in an older version (don't remember which one) and boost threads.
Can you give details about the version you used?. Also try it with 2.4.5.