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ros2_migration_readme.md

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This document contains the overview of the bond-core package, build and test procedure to test package and the changes made with respect to migration of bond-core from ROS to ROS2. Later current limitations are also listed down.

Overview

A bond allows two processes, A and B, to know when the other has terminated, either cleanly or by crashing. The bond remains connected until it is either broken explicitly or until a heartbeat times out.
Constructor of object is as follows,
bond::Bond::Bond(
  const std::string & topic, const std::string & id, rclcpp::Node::SharedPtr nh,
  std::function<void(void)> on_broken,
  std::function<void(void)> on_formed)

Parameters
    topic      : The topic used to exchange the bond status messages.
    id	       : The ID of the bond, which should match the ID used on the sister's end.
    nh         : The node used to from bond
    on_broken  : Callback that will be called when the bond is broken.
    on_formed  : Callback that will be called when the bond is formed. 

Bond-core (CPP) is have following functionalities as per ROS.

 start() : Starts the bond and connects to the sister process.
 setFormedCallback(std::function<void(void)> on_formed) : Sets the formed callback.
 setBrokenCallback(std::function<void(void)> on_broken) : Sets the broken callback.
 waitUntilFormed(rclcpp::Duration timeout) : Blocks until the bond is formed for at most 'duration', timeout Maximum duration to wait.
 waitUntilBroken(rclcpp::Duration timeout) : Blocks until the bond is broken for at most 'duration', timeout Maximum duration to wait.
 isBroken() : Indicates if the bond is broken.
 breakBond() : Breaks the bond, notifying the other process.
 getTopic() : Gets topic name.
 getId() : Gets ID.
 getInstanceId() : Gets instant ID.
 getConnectTimeout() : Gets connect timeout in nanoseconds.
 setConnectTimeout(double dur) : Sets connect timeout in seconds.
 getDisconnectTimeout(): Gets disconnect timeout in nanoseconds.
 setDisconnectTimeout(double dur) : Sets disconnect timeout in seconds.
 getHeartbeatTimeout() : Gets heatrbeat timeout in nanoseconds.
 setHeartbeatTimeout(double dur) : Sets heartbeat timeout in seconds.
 getHeartbeatPeriod() : Gets heartbeat period (publishing period) in naoseconds.
 setHeartbeatPeriod(double dur) : Sets heartbeat period (publishing period) in seconds.
 getDeadPublishPeriod() : Gets dead publish period in nanoseconds.
 setDeadPublishPeriod(double dur) : Sets dead publish period in seconds.

Build proccedure and testing

    1. Get pacakge at local system

            1.1 # mkdir -p ros2_ws_bond/src

            1.2 # cd ros2_ws_bond/src

            1.3 # git clone git@github.com:kishornaik10/bond_core.git
	    or git clone https://github.com/kishornaik10/bond_core.git 
	    (checkout for ros2-devel branch)

            1.4 # source /opt/ros/crystal/setup.sh


    2. Build the package

             2.1 # cd ../
             2.2 # colcon build

    3. Do the test

             3.1 # colcon test

    4. The executables are generated follow the below steps to run tests.

            4.1 source local setup

             # source install/local_setup.sh

            4.2 run the executables.
		./install/test_bond/lib/test_bond/exercise_bond_cpp_exc
		./install/test_bond/lib/test_bond/test_callbacks_cpp_exc

ROS2 Migration changes

The basic concept and design are same as ROS.
All changes for migration have been done as per Migration guide.
1. Node is passed to a constructor of bond class.
2. The timeout class is removed and steady timer is replaced by wall timer.
3. a) For each timer, timeout time is set.
   b) Callback function is written in such a way that it will be called on valid request, so flag is used.
4. waitUntilFormed  and  waitUntilBroken functions modified, locking system removed to handle callback of node as Callback Queue is not available in ROS2.

Limitations

1. Work around is done for timer.
2. CallbackQueue is not available hence function related to Callback Queue commented out.
3. Dead publising period and timer is not used.
4. bondpy needs to be migrate.