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Problem with threads and callback

asked 2020-08-07 08:29:17 -0500

Pombor gravatar image

updated 2022-01-22 16:10:42 -0500

Evgeny gravatar image

Hi, I would like to create a program that's a subscriber and listener at the same time.

Here my diagram that I made just for this :

image description

My callback is a listener that is initialized with ros::spin() in the beginning of the program (but i'm not sure that's the good one).

When it receives the good message, it will change the value of a boolean. With that modified value it will automaticly stop or continue the publisher.

I have 2 choices :

  • The publisher is in a while which is initialized in the beginning of the program (that is to say : i remove ros::spin() in main to write ros::spinOnce() in the while). With a "If", it will stop the publish without exit the while.
  • The publisher is in a while inside the callback.

In these two cases, I have one problem : it will never stop the loop (if it's in constructor, it will create an infinite loop, if it's in callback, i don't have any problem with infinite loop if I press CTRL + C). I change the boolean value in the callback, just after received message.

CASE 1 :

void Selectcamera::selectCallback(const std_msgs::String::ConstPtr &msg)
{
    if (msg->data == "STOP")
       isOk = false;
    else
       isOk = true;
    while (isOk == true) {
        cap >> frame;
        cvimage = cv_bridge::CvImage(std_msgs::Header(), "bgr8", frame).toImageMsg();
        pub.publish(cvimage);
        cv::waitKey(1);
    }
}

void Selectcamera::Selectcamera()
{
    ros::init(argc, argv, "selectcamera");

    ros::NodeHandle selectcamera;

    image_transport::ImageTransport it(camera);
    pub = it.advertise("camera", 1);

    listcam_subscriber = selectcamera.subscribe("device", 1, &Selectcamera::selectCallback, this);

    ros::spin();
}

CASE 2 :

void Selectcamera::selectCallback(const std_msgs::String::ConstPtr &msg)
{
    if (msg->data == "STOP")
       isOk = false;
    else
       isOk = true;
}

void Selectcamera::Selectcamera()
{
    ros::init(argc, argv, "selectcamera");

    ros::NodeHandle selectcamera;

    image_transport::ImageTransport it(camera);
    pub = it.advertise("camera", 1);

    listcam_subscriber = selectcamera.subscribe("device", 1, &Selectcamera::selectCallback, this);

    while (ros::ok()) {
        if (isOk == true) {
            cap >> frame;
            cvimage = cv_bridge::CvImage(std_msgs::Header(), "bgr8", frame).toImageMsg();
            pub.publish(cvimage);
        }
        cv::waitKey(1);
        ros::spinOnce();
    }
}

What is the best solution and how can I make it ?

Thanks,

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answered 2020-08-10 01:26:50 -0500

Pombor gravatar image

No answer ?

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Asked: 2020-08-07 08:29:17 -0500

Seen: 59 times

Last updated: Aug 07 '20