DDS tutorial with connector

©2017 Real-Time Innovations,
Inc.
Tutorial: DDS first steps with Connector
Javier Povedano, PhD.
javier@rti.com
Real-Time Innovations Inc.

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Agenda
• DDS
• Connector
• Setup your environment
• Hands On!
– Publishing/Subscribing to Data
– Data Filtering
– High-Availability
– Late joiners
– Partitions

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DDS Shapes Demo
https://www.rti.com/downloads/shapes-demo

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What is Connector?
• Simple API for Data-Centric Publish/Subscribe
– Built on top of DDS
– Very few methods
– Experimental
• Scripting language bindings
– node.js, python, nodered
• Prototyping
– Entities and QoS configured by XML

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2016 © Real-Time Innovations Inc.
Classical DDS Workflow
IDL/XML
struct Position2D {
long id; //@key
double x;
double y;
};
Code
Generation
struct Temp {
long id;
//@key
double
value;
};
struct Temp {
long id;
//@key
double
value;
};
#include <...>
define Position2D;
Pos2DWriter::write
Pos2DReader::read
C/C++/Java/C#
<xml QoS>
QoS Settings
Type
Definition
Code ready to be built in +50 architectures: Linux, Windows,
VxWorks, Integrity….
This process can be simplified even more: RTI
Prototyper/Connector

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Connector Workflow
Python/Lua/NodeJS
Interpreter
<xml QoS>
<types>
<scenario description>
Python/Lua/NodeJS
script

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Input
Data Port
(DataReader+)Output
Data Port
(DataWriter+)
DDS Connector Input & Output ports
Connector (DomainParticipant+)
output()
write() / dispose() /
unregister()
clear_members()
instance
input()
wait() / on()
read() / take()
samples[]
config.xml
User
Defined
Structure
XML Config

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Anatomy of a Publisher in Connector
1. connector =
rti.Connector("MyParticipantLibrary::Sensor",'Tutorial.xml')
2. writer = connector.getOutput("TempPublisher::TempWriter")
3. writer.instance.setString('id', sensor.id)
4. writer.write()
1. Create a connector
2. Get the DataWriter
3. Set the instance values
4. Write the value

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Anatomy of a Subscriber in Connector
1. connector = rti.Connector("MyParticipantLibrary::Sensor", 'Tutorial.xml')
2. reader = connector.getInput("TempPublisher::TempWriter")
3. reader.read()
4. for i in nsamples:
if reader.infos.isvalid(i)
sample = reader.samples.getDictionary(i)
1. Create a connector
2. Get the datareader
3. Read/Take the value
4. Iterate for all the samples
a. if is valid
i. get the sample

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Setup
Installing the tutorial
> git clone https://github.com/jpovedano/dds-firststeps
> ./setup
In each terminal:
> . rticonnectenv/bin/activate

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Let's Rock!
Hands On Exercise

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About the examples
• Temperature sensor scenario
– Sensors (publishers)
• Publish temperature data every
second
– Console (suscribers)
• Shows a table with data being
published
• Configured by XML
– Tutorial.xml
• Define the DDS entities and their QoS
settings
struct Sensor {
string id; //@key
long value;
long timestamp;
};

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Anatomy of the XML
1. QoS Library
a. QoS Settings
2. Types
a. Type Definition
3. Domain Library
a. Domains and Topics
4. Participant Library
a. DDS Entities hierarchy

<qos_library name="QosLibrary">
<qos_profile name="DefaultProfile" is_default_qos="true">
<participant_qos>
<transport_builtin>

<mask> SHMEM</mask>
</transport_builtin>
</participant_qos>
<datareader_qos>

</datareader_qos>
</qos_profile>
</qos_library>

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Anatomy of the XML
1. QoS Library
a. QoS Settings
2. Types
a. Type Definition
3. Domain Library
<types>
<struct name="Sensor" extensibility="extensible">
<member name="id" stringMaxLength="128" id="0" type="string"
key="true"/>
<member name="value" id="1" type="long"/>
<member name="timestamp" id="2" type="long"/>
</struct>
</types>

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Anatomy of the XML
1. QoS Library
a. QoS Settings
2. Types
a. Type Definition
3. Domain Library

<domain_library name="MyDomainLibrary">
<domain name="MyDomain" domain_id="0">
<register_type name="Sensor" kind="dynamicData"
type_ref="Sensor"/>
<topic name="Temperature" register_type_ref="Sensor"/>
</domain>
</domain_library>

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Anatomy of the XML
1. QoS Library
a. QoS Settings
2. Types
a. Type Definition
3. Domain Library

<participant_library name="MyParticipantLibrary">
<domain_participant name="Console"
domain_ref="MyDomainLibrary::MyDomain">
<subscriber name="TempSubscriber">
<data_reader name="TempReader" topic_ref="Temperature"/>
</subscriber>
</domain_participant>
<domain_participant name="Sensor"
domain_ref="MyDomainLibrary::MyDomain">
<publisher name="TempPublisher">
<data_writer name="TempWriter" topic_ref="Temperature"/>
</publisher>
</domain_participant>
</participant_library>

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Example 1: Basic pub/sub
• Goal
– In this example we show how to publish data
– Learn differences between read/take
– Learn how to change QoS settings in Connector
• Documentation:
– QoS Policy Reference Guide (cheat-sheet)

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Example 2: Filtering
• Goal
– Learn how to filter data per subscriber
• Description
– The console application will only receive the data matching a
certain criteria
• Two types of Filtering:
– Content Based
• Use a filter with SQL Expression
– Time Based
• time_based_filter QoS

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Example 3: High availability
• Goal
– Learn how to add robustness using DDS QoS
• Description
– Adding a backup sensor that substitute the primary sensor in case
of failure
• QoS:
– Liveliness
– Ownership
– Ownership strength

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Example 4: Durability
• Goal
– Learn how to provide recent history to late joiners
• Description
– A console application will receive the recent history published
before it was started
• QoS:
– Durability QoS

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Example 5: Data Isolation/Partition
• Goal
– Learn how to isolate publishers and subscribers within the same
domain
• Description
– A console application will receive sensor updates only for
subscribers in certain zones
• QoS:
– Partition QoS

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Example 6
• Goal
– create your own distributed application and share it with the
community
• Description
– Let your imagination fly!
• References
– XML Application creation

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Thanks for your attention!

DDS tutorial with connector

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