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

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://www.ros.org/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://www.ros.org/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://www.ros.org/wiki/roscpp/NewMessageAPIProposal and http://www.ros.org/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://www.ros.org/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://www.ros.org/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

• Messages
  • Message generators have been rewritten in Python
  • Constants (including string constants) are now properly supported, and should never generate compiler or linker errors
  • serialization is now bounds checked and should not crash if invalid serialized data is received

  • Messages can now be printed to a std::ostream using operator<<

• CallbackQueue::callAvailable() and callOne() methods are now recursive-safe, so you can call either of them from within a callback being invoked from the same CallbackQueue

• Subscribing with * as the md5sum/datatype now decays to a real type (which then never changes) as soon as it receives the md5sum in any way (e.g. a publisher connects or a 2nd subscriber in the same node)

• Added parameter validation to a number of methods. They will throw a ros::InvalidParameterException if invalid

• advertise() no longer accepts the * datatype/md5sum

Major Bugs Fixed

• Fixed possible starvation of subscription callbacks
• Long-running timer callbacks no longer starve callbacks running from the same callback queue in different threads

• No longer allows (silently with bugs) subscribing to the same topic with multiple different data types. Will throw a ros::ConflictingSubscriptionException in this case

• UDPROS now verifies topic md5sums

• Fixed a number of bugs with UDPROS

• Fixed a race condition that caused some connections to immediately close. Generally exposed itself as failed service calls if they were happening in quick succession.

Deprecations

• set_X_size()/get_X_size() message accessors

• Message::__getMD5Sum()

• Message::__getDataType()

• Message::__getMessageDefinition()

• Message::__s_getMD5Sum()

• Message::__s_getDataType()

• Message::__s_getMessageDefinition()

• Message::__connection_header

• Message::serializationLength()

• Message::serialize()

• Message::deserialize()

• Message::__serialized_length