OpenCV从缓冲区写入和读取 [英] Opencv writing and reading from a buffer

问题描述

我有两个任务(线程)，每个任务运行在不同的处理器(核心)上，第一个任务使用OpenCV videocapture()重复捕获图像.

I have two tasks (Threads) each task runs on a different processor(core), the first capture an image repeatedly using OpenCV videocapture().

我仅将这两行用于捕获:

I only used these two lines for the capture :

cv::Mat frame;
capture.read(frame);

现在，我想使用第二个任务显示捕获的图像.在第二个任务的代码中执行imshow函数后:

Now I want to display the captured image using the second task. After executing the imshow function within the second task's code :

cv::imshow("Display window", frame);

我收到以下输出错误:

OpenCV Error: Assertion failed (size.width>0 && size.height>0) in imshow, file /build/opencv-L2vuMj/opencv-3.2.0+dfsg/modules/highgui/src/window.cpp, line 304
terminate called after throwing an instance of 'cv::Exception'
what():  /build/opencv-L2vuMj/opencv-3.2.0+dfsg/modules/highgui/src/window.cpp:304: error: (-215) size.width>0 && size.height>0 in function imshow

那么，如何避免此错误?

So, how can I avoid this error?

完整的代码位于 Github

推荐答案

您的代码存在的问题是存在数据争用.尝试在读取之前显示它，以便您可以看到问题 如果需要同步解决方案，则可以使用pthread条件&等到读取图像以指示您的显示功能，否则您将一直处于等待状态！

The problem with your code is that there is a data race.. Imagine the display thread goes first lock the frame & try to display it before it is read so as you can see the problem If you want a synchronized solution you can use the pthread condition & wait till an image is read to signal your display function otherwise you are gonna have an active wait!!

// in the declaration part 
// Declaration of thread condition variable 
pthread_cond_t cond1 = PTHREAD_COND_INITIALIZER; 

//in the display function 

ptask DisplyingImageTask()
{

    int task_job = 0;

    while (1)
    {
        std::cout << "The job " << task_job << " of Task T" << ptask_get_index()
                  << " is running on core " << sched_getcpu() << " at time : "
                  << ptask_gettime(MILLI) << std::endl;

        cv::namedWindow("Display window", cv::WINDOW_AUTOSIZE);

        pthread_mutex_lock(&frame_rw);
        //wait for the read function to send a signal
        pthread_cond_wait(&cond1, &frame_rw);

        cv::imshow("Display window", frame);        
        cv::waitKey(1);

        pthread_mutex_unlock(&frame_rw);

        ptask_wait_for_period();
        task_job++;
    }

}

// in the Read function

ptask CapturingImageTask()
{

    int task_job = 0;

    while (1)
    {
        std::cout << "The job " << task_job << " of Task T" << ptask_get_index()
                  << " is running on core " << sched_getcpu() << " at time : "
                  << ptask_gettime(MILLI) << std::endl;

        pthread_mutex_lock(&frame_rw);
        capture.read(frame);
        //after capturing the frame signal the display function & everything should be synchronize as you want 
        pthread_cond_signal(&cond1);  

        pthread_mutex_unlock(&frame_rw);

        ptask_wait_for_period();
        task_job++;
    }

}

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