Re: Threading problems

Sorry, my mistake..I had an update method that did camera_get_image after
each robot_step, thus when update was called from a thread the problem
occured. Now it works fine. Thanks.

/Anders.

> Hi,
>
> It seems the following threaded program works fine on my Windows XP
> machine with Webots 4.0.20 (see attachment). What error (if any) do you
> get ?
>
> -Olivier
>
> Anders Lyhagen wrote:
>
> >Hi,
> >
> >The problem occurs when you make a call (from a thread) to any method
> >in the webots API (camera_get_image, servo_set_position, robot_step
> >etc).
> >I solved the image processing the way you mentioned but I would like to
> >thread some movements as well, however, that is
> >impossible (with XP). Might install Linux though..
> >
> >Best,
> >Anders L
> >
> >
> >
> >>Hi,
> >>
> >>I could reproduce this problem and tryed to fix it but it is not
> >>easy...
> >>Strangely enough, this problem occurs only under Window. The program
> >>appear to work fine under Linux... Actually under Windows the same
> >>OpenGL context cannot be shared among different threads, instead
> >>different OpenGL context should be used in each thread which cause some
> >>problems with initialization and cleanup which is done by the main
> >>thread...
> >>
> >>It would be possible to create a special subclass the java Thread that
> >>would work with camera, but it would complicate the programming API.
> >>
> >>Instead, I would recommand you that only the main Thread should do the
> >>image acquisition, i.e., camera_enable() and subsequent
> >>camera_get_image() while you can distribute the image processing on
> >>other Threads. The int array receiving the image should be global
> >>variable to be shared between threads. Of couse, this requires some
> >>basic Thread synchronization to work well.
> >>
> >>-Olivier
> >>
> >>Olivier Michel wrote:
> >>
> >>
> >>
> >>>Anders Lyhagen wrote:
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>>Hi,
> >>>>
> >>>>Does anyone know why this code yields a "cannot activate openGL
> >>>>context"
> >>>>error?
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>I recently made the Webots API MT-safe, but this was not enough to fix
> >>>that problem. It seems that the OpenGL context is not inherited in
> >>>subsequent Java Threads. I will try to sort that out as it is
> >>>becoming a
> >>>recurrent question... Thanks for the source code which is very simple
> >>>and shows nicely the problem.
> >>>
> >>>-Olivier
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>>import com.cyberbotics.webots.Controller;
> >>>>public abstract class Judoka0 extends Controller {
> >>>>  static int camera;
> >>>>
> >>>>  public static void reset() {
> >>>>      camera = robot_get_device("camera");
> >>>>  }
> >>>>
> >>>>  public static void main() {
> >>>>      camera_enable(camera, 64);
> >>>>
> >>>>      Sensors sensors = new Sensors();
> >>>>      sensors.setPriority(Thread.MIN_PRIORITY);
> >>>>      sensors.start();
> >>>>
> >>>>      while(true)
> >>>>          robot_step(64);
> >>>>  }
> >>>>
> >>>>  static class Sensors extends Thread {
> >>>>       public void run() {
> >>>>          while(true) {
> >>>>              int[] img = camera_get_image(camera);
> >>>>              try {
> >>>>                  thread.sleep(200);
> >>>>              }
> >>>>              catch(Exception e){}
> >>>>          }
> >>>>      }
> >>>>  }
> >>>>}
> >>>>
> >>>>Best regards,
> >>>>Anders.L
> >>>>
> >>>>
> >
> >
> >
> >
> >
>
>
>
> Yahoo! Groups Links
>
>
>
>
>


----------------------------------------------------------------------------
----


> import com.cyberbotics.webots.Controller;
> import java.io.*;
>
> public abstract class Judoka0 extends Controller {
>   public static void die() {
>     System.out.println("die method called");
>   }
>   static int joint;
>   public static void reset() {
>     joint=robot_get_device("back_1");
>   }
>   public static void main() {
>     servo_enable_position(joint,64);
>     Motion motion = new Motion();
>     motion.setPriority(Thread.MIN_PRIORITY);
>     motion.start();
>     while(true) robot_step(64); // run one step
>   }
>   static class Motion extends Thread {
>     public void run() {
>       float pos=0;
>       while(true) {
>         servo_set_position(joint,pos);
> pos+=0.05;
> try {
>   Thread.sleep(200);
> } catch(Exception e) {}
>       }
>     }
>   }
> }
>




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