Why does NodeHandle hang? - ros

Question

I'm having an issue trying to create a subscriber in Indigo. I have a shared_ptr within a class to hold the NodeHandle object. I do this so that NodeHandle can be used in other class members. The problem is when the thread starts, it seems to hang on the make_shared call to the NodeHandle object within the MyClass constructor as it never reaches the next line after.
class MyClass
{
private:
std::shared_ptr<ros::NodeHandle> nh;
std::map<std::string, std::string> remap;
// ...
};
MyClass::MyClass()
{
// remap is empty
ros::init(remap, "my_node");
nh = make_shared<ros::NodeHandle>();
cout << "does not reach this line" << endl;
}
int MyClass::run()
{
// ...
}
I start the thread liks so ...
{
// ...
myobj = make_shared<MyClass>();
my_thread = thread(&MyClass::run, myobj);
// ...
}
Thoughts?

Answer 1

It appears that the problem was due to having my own boost logging system in place and not using the ROS logger (which made it difficult to find as it seemingly has nothing to do with ros::NodeHandle, but probably does underneath). I would comment out my entire code base and start adding to see when ros::NodeHandle would run and at the point of removing my logger and adding it back, I would see the difference between it running and hanging.

Answer 2

Well, here's an example of using Boost::make_shared for a nodehandle.
Note that it makes use of ros::NodeHandlePtr, an already existant Boost shared pointer not using the "std::make_shared" one.
This maybe does not really answer the question but I am suggesting another way around using the boost library.
#include <ros/ros.h>
#include <std_msgs/Empty.h>
#include <boost/thread/thread.hpp>
void do_stuff(int* publish_rate)
{
ros::NodeHandlePtr node = boost::make_shared<ros::NodeHandle>();
ros::Publisher pub_b = node->advertise<std_msgs::Empty>("topic_b", 10);
ros::Rate loop_rate(*publish_rate);
while (ros::ok())
{
std_msgs::Empty msg;
pub_b.publish(msg);
loop_rate.sleep();
}
}
int main(int argc, char** argv)
{
int rate_b = 1; // 1 Hz
ros::init(argc, argv, "mt_node");
// spawn another thread
boost::thread thread_b(do_stuff, &rate_b);
ros::NodeHandlePtr node = boost::make_shared<ros::NodeHandle>();
ros::Publisher pub_a = node->advertise<std_msgs::Empty>("topic_a", 10);
ros::Rate loop_rate(10); // 10 Hz
while (ros::ok())
{
std_msgs::Empty msg;
pub_a.publish(msg);
loop_rate.sleep();
// process any incoming messages in this thread
ros::spinOnce();
}
// wait the second thread to finish
thread_b.join();
return 0;
}
In case you get trouble with the CMakeLists, here it is :
cmake_minimum_required(VERSION 2.8.3)
project(test_thread)
find_package(catkin REQUIRED COMPONENTS
roscpp
rospy
)
find_package(Boost COMPONENTS thread REQUIRED)
include_directories(${Boost_INCLUDE_DIR})
catkin_package(CATKIN_DEPENDS roscpp rospy std_msgs)
include_directories(include ${catkin_INCLUDE_DIRS})
add_executable(thread src/thread_test.cpp)
target_link_libraries(thread ${catkin_LIBRARIES} ${BOOST_LIBRARIES})
Hope that helps !
Cheers,