尝试使用线程运行CamShift

Question

I wrote code that creates 2 threads (I'm using glib). The first thread runs a function called Camera that just starts capturing from the camera, and shows the captured frames on the screen. The second function is the algorithm CamShift that uses the captured image from the first function to start running. I made the first function to capture from the camera because later I will add more algorithms like CamShift that will access the captures from the first function.

My problem is that I want these 2 functions to continue running until I tell them to stop. But I'm new using threads and the way I wrote the code it compiles fine and runs the 2 functions, but they just "pause" immediately after they start. Below is the code of my 2 functions.

//**********Sensa iluminacion (hilo)******************************************
GThread      *idGHilo,*idGHilo1, *idGHilo2, *idGHilo3, *idGHilo4;
GError       **error = NULL;
char *valorDevuelto = NULL;/* Valor que va a devolver el thread hijo */
if(!g_thread_supported()) // se inicializa el sistema de hilos (se emplea cuando  se
    g_thread_init( NULL );   // emplean más de un hilo


idGHilo1 = g_thread_create( (GThreadFunc) Camara, NULL, TRUE, error );//esto lo  cambie ayer 23
/* Comprobamos el error al arrancar el thread */
if(error) {
    g_print( "Error: %s\n", error[0]->message );
    g_error_free( error[0] );
    //exit (-1);
}
sleep( 10 );          // se da un retardo para dar tiempo a que termine el hilo
idGHilo2 = g_thread_create( (GThreadFunc) CamShift2, NULL, FALSE, error );
if(error) {
    g_print( "Error: %s\n", error[0]->message );
    g_error_free( error[0] );
    //exit (-1);
}
sleep( 10 ); //10...5
g_thread_join( idGHilo1 );
g_thread_join( idGHilo2 );


//****************************
// This is the camera function
void Camara() {

    capture = cvCaptureFromCAM( 0 );
    while( stop != 's' ) {

        // get a frame 
        frame = cvQueryFrame( capture );

        // always check 
        if( !frame ) break;

        // 'fix' frame 
        cvFlip( frame, frame, 2 );
        frame->origin = 0;

        cvNamedWindow( "Camara", CV_WINDOW_AUTOSIZE );
        cvShowImage( "Camara", frame );

        // quit if user press 'q' 

        stop = cvWaitKey( 10 );
    }
}

The other function is the regular CamShift algorithm that comes with OpenCV. I just modified it to use the captured frames from the Camera function. That works fine, but the problem is, like I said before, the 2 functions start and then just pause.

Answer 1

Don't use sleep to try to synchronize the threads. You need to be protecting the frame variable with either a GMutex , or a GStaticRWLock . This will prevent race conditions from occurring with that shared resource. You could also notify the CamShift thread that a frame is ready (in the Camera thread) using the GCond condition variable structure. This will allow the CamShift thread to block until a frame is captured in the Camera thread.

Hope that is helpful!