Time Synchronizer hangs after few messages

edit

enter code hereHi,

I have a scenario where I have 2 sensors publishing messages to 2 different topics, let's say:

topicA

topicB

I wanted to subscribe to both these topics using a 3rd node; compare the values from the first 2 topics and do certain operations and generate a new output to be published onto another topic say,

topicC

For this I created custom messages for each of my sensors with a header containing the time stamp.

In the nodes publishing to topics 'topicA' and 'topicB' I initialized the timestamp field in the header as

x.header.timeStamp = ros::Time::now()

All my publisher nodes run continuously with no problems. However, I only get the first two messages at the output of my synchronizer and then it stops forever. Then I am unable to stop the node other than terminating the execution using SIGINT (ctrl+z).

Can someone tell me what I can do so that my timesynchronizer works properly and synchronizes the outputs from topicA and topicB using timestamps.

Here's the code of node 3:

void fusionCallback(const fusion::TwistsConstPtr& sensorA, const fusion::TwistsConstPtr& sensorB)
geometry_msgs::Twist vel;
ros::NodeHandle n;
ros::Publisher vel_pub = n.advertise<geometry_msgs::Twist>("/cmd_vel", 1);
ros::Rate loop_rate(10);
while(ros::ok())
{
    float sensorA_dat = sensorA->dat;
    float sensorB_dat = sensorB->dat;
    if(sensorB_dat > sensorA_dat)
        vel = sensorB->vel;
    else vel = sensorA->vel;
    vel_pub.publish(vel);
    ROS_INFO("sensorA Data = [%f] sensorB Data = [%f]", sensorA_dat, sensorB_dat);
    ros::spinOnce();
    loop_rate.sleep();

}

int main(int argc, char **argv)

ros::init(argc, argv, "vel_publisher");
ros::NodeHandle n;
//ros::Rate loop_rate(20);

using namespace message_filters;
Subscriber<fusion::Twists> sensorA_sub(n, "/fusion/cmd_vel_sensorA", 1);
Subscriber<fusion::Twists> sensorB_sub(n, "/fusion/cmd_vel_sensorB", 1);


typedef sync_policies::ApproximateTime<fusion::Twists, fusion::Twists> MySyncPolicy;

Synchronizer<MySyncPolicy> sync(MySyncPolicy(100), sensorA_sub, sensorB_sub);
sync.registerCallback(boost::bind(&fusionCallback, _1, _2));
ros::spin();

return 0;

}

Note: All braces are proper in the actual code!

Update : The Effect of spin inside callback

On the suggestion of @dornhege I tried removing the spin inside callback and then my code started working. I was able to see the output wherein the TimeSynchronizer merged the data from both the topics appropriately. I was able to terminate the execution using ctrl+c as well.

However, the problem is that now my output is not getting published. Infact, that is the reason why I have the spin inside the callback. This is as per the basic tutorials for publisher and subscriber provided here

Thanks and Regards.