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detecting timeout from waitForMessage

asked 2013-08-15 23:07:13 -0500

wesleyc gravatar image

updated 2013-08-20 14:35:15 -0500

Hi,

I'm using the waitForMessage function and can't seem to be able to find a way of detecting if the function has timed out.

Here's the code I have:

sensor_msgs::PointCloud2 pc;
pc  = *(ros::topic::waitForMessage<sensor_msgs::PointCloud2>(rgb_topic_, ros::Duration(10)));

How can I check and see if pc is valid?

If I try to read the fields of pc when it has timed out, the code exits with the following error:

calibration_executive: /usr/include/boost/smart_ptr/shared_ptr.hpp:412: boost::shared_ptr<T>::reference boost::shared_ptr<T>::operator*() const [with T = const sensor_msgs::PointCloud2_<std::allocator<void> >, boost::shared_ptr<T>::reference = const sensor_msgs::PointCloud2_<std::allocator<void> >&]: Assertion `px != 0' failed.
Aborted

By the way, the code is from the pr2_led_kinect_calib package.

Thanks.

------------------- update ------------------

Tried putting it in a try catch block but it didn't work

    try
    {
        pc  = *(ros::topic::waitForMessage<sensor_msgs::PointCloud2>(rgb_topic_, ros::Duration(10)));
        if ((after == ros::Time(0,0)) || (pc.header.stamp > after))
        {
            found = true;
        }   

    }
    catch (std::exception e)
    {
        ROS_ERROR("No point clound messages received in topic %s after waiting for %f seconds.", rgb_topic_.c_str(), waitTime);
        continue;
    }

It aborts at

    if ((after == ros::Time(0,0)) || (pc.header.stamp > after))

and no exception is thrown.

Also tried

if (!pc)

But pc is not a pointer so it gives a type mismatch compilation error.

------------------- update ------------------

Thanks for the responses!

As suggested, I tried storing the returned value as a shared pointer, then checking to see if it's NULL, and that worked.

boost::shared_ptr<sensor_msgs::PointCloud2 const> sharedPtr;
sensor_msgs::PointCloud2 pc;

sharedPtr  = ros::topic::waitForMessage<sensor_msgs::PointCloud2>(rgb_topic_, ros::Duration(10));
    if (sharedPtr == NULL)
        ROS_INFO("No point clound messages received);
    else
        pc = *sharedPtr;
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Comments

What if you define pc as a pointer (PointCloud2Ptr pc) and then check if it points to zero?

timster gravatar imagetimster ( 2013-08-16 02:02:44 -0500 )edit

This will also work:

sensor_msgs::PointCloud2 pc;
sensor_msgs::PointCloud2ConstPtr msg = ros::topic::waitForMessage<sensor_msgs::PointCloud2>(rgb_topic_, ros::Duration(10));
    if (msg == NULL)
        ROS_INFO("No point clound messages received);
    else
        pc = * msg;
sven-cremer gravatar imagesven-cremer ( 2015-01-02 14:22:03 -0500 )edit

2 Answers

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answered 2013-08-16 03:55:14 -0500

dornhege gravatar image

updated 2013-08-16 03:55:26 -0500

I'd image the best way is to NOT assign the pointcloud, but use a shared pointer.

If the functions times out that shared pointer should be empty. You also see the sensor_msgs::PointCloud2_<std::allocator<void> >&]: Assertion px != 0' failed. pop up. You can check that before.

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answered 2013-08-16 00:27:40 -0500

timster gravatar image

I use a try-catch block for tf::TransformListener::waitForTransform. In your case, I would try something like:

sensor_msgs::PointCloud2 pc;
try
{
    pc  = *(ros::topic::waitForMessage<sensor_msgs::PointCloud2>(rgb_topic_,ros::Duration(10)));
}
catch()
{
    ROS_WARN("something");
}
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Comments

Unfortunately I've tried that and it didn't work. The call to waitForMessage returns normally. But after that when the next line does if ((after == ros::Time(0,0)) || (pc.header.stamp > after)) it causes the program to abort. No exception is being thrown by waitForMessage or pc.header.stamp.

wesleyc gravatar imagewesleyc ( 2013-08-16 01:26:15 -0500 )edit

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Asked: 2013-08-15 23:07:13 -0500

Seen: 6,657 times

Last updated: Aug 20 '13