[Documentation] [TitleIndex] [WordIndex] 

This page describes major changes to roscpp applicable to the 1.2 release.

Contents

  1. Message/Service Changes
  2. Publish/Subscribe Changes
  3. Subscription TCP Connection Retry
  4. Time Gotchas

Major Changes

Message/Service Changes

New Serialization API

Serialization has turned from polymorphic to template-based. This removes the need for a Message base-class, and allows you to adapt existing C++ structures to ROS messages. See http://wiki/roscpp/Overview/MessagesSerializationAndAdaptingTypes for information on adapting types to ROS msg types.

An example use of this is to adapt builtin types to the std_msgs types. For example, the following is now possible: 

   1 #include <std_msgs/builtin_uint32.h>
   2 void callback(uint32_t val)
   3 {
   4 }
   5 
   6 ros::Subscriber sub = nh.subscribe("my_topic", 0, callback);
   7 ros::Publisher pub = nh.advertise<uint32_t>("my_topic", 0);
   8 pub.publish(5);

Use of the Message base-class and members (__getMD5Sum(), __connection_header, etc.) are now deprecated. md5sum/etc. retrieval is now done through traits: http://wiki/roscpp/Overview/MessagesTraits. The connection header is now accessible through a new type of callback argument, MessageEvent in a subscription callback: 

   1 void callback(const ros::MessageEvent<Msg const>& evt)
   2 {
   3   ros::M_string& header = evt.getConnectionHeader();
   4 }

Or ServiceEvent in a service callback: 

   1 void callback(const ros::ServiceEvent<Request, Response>& evt)
   2 {
   3   ros::M_string& header = evt.getConnectionHeader();
   4 }

For the rationale behind these changes as well as some implementation details, please see http://wiki/roscpp/NewMessageAPIProposal and http://wiki/roscpp/NewMessageAPIProposal2

This change is backwards compatible. Old-style custom C++ messages will continue to work without changes until ROS 2.0, and messages will continue deriving from the Message base class until then as well.

Custom Allocator Support

Messages can now use an STL allocator of your choosing to do their container memory allocation. 

   1 ROS_DECLARE_MESSAGE_WITH_ALLOCATOR(visualization_msgs::Marker, MyMarker, MyAllocator);
   2 MyMarker marker;
   3 MyAllocator a;
   4 MyMarker marker2(a);
   5 ...

See http://wiki/roscpp/Overview/MessagesCustomAllocators

Publish/Subscribe Changes

Subscription Callback Types, Non-Const Subscriptions

In addition to MessageEvent shown above, it's now possible to use a number of different signatures for your callback: 

   1 void callback(const boost::shared_ptr<Msg const>&);
   2 void callback(boost::shared_ptr<Msg const>);
   3 void callback(const Msg&);
   4 void callback(Msg);

You can also now request a non-const message, in which case a copy will be made if necessary (i.e. there are multiple subscriptions to the same topic in the same node). 

   1 void callback(const boost::shared_ptr<Msg>&);

These callback types are now supported in message_filters as well.

See http://wiki/roscpp/Overview/Publishers%20and%20Subscribers#Callback_Signature

Fast Intraprocess Message Passing

It's now possible to send messages within a node without incurring a serialize/deserialize cost: 

   1 MsgPtr g_msg;
   2 void callback(const MsgConstPtr& msg)
   3 {
   4   ROS_ASSERT(msg == g_msg); // Should not fire
   5 }
   6 
   7 ros::Subscriber sub = nh.subscribe("my_topic", 0, callback);
   8 ros::Publisher pub = nh.advertise<Msg>("my_topic", 0);
   9 MsgPtr msg(new Msg);  // Note that this is a boost::shared_ptr
  10 g_msg = msg;
  11 pub.publish(msg);
  12 
  13 // The following would *not* be no-copy
  14 // Msg msg;
  15 // pub.publish(msg);
  16

Generated msg/srv Header Location Change

Generated .msg/.srv headers now go into <package>/msg_gen and <package>/srv_gen respectively. Their include paths are automatically exported, and roswtf will now warn if you have -I${prefix}/msg/cpp in your manifest exports.

Subscription TCP Connection Retry

If a TCP connection to a publisher fails for any reason, roscpp will now attempt to retry that connection until it is notified by the master that the node has gone away.

The retry starts at 100ms after the connection is dropped, and backs off by doubling that time after every failure until it hits 20s.

Time Gotchas

roscpp no longer allows use of ros::Time::now() until the node has been started, either through the creation of the first NodeHandle or through ros::start(). This is because we cannot know if we're using simulation time until we check the /use_sim_time parameter, and thus whatever time we return may be invalid.

If and only if you know you're not in a Node (like in a unit test), you can call ros::Time::init(). You can also use ros::WallTime in this case.

Additional Changes

Major Bugs Fixed

Deprecations

2024-12-21 13:05