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![Anatomy of a DDS Application
[DDS C++ API 2010]
Domain
Domain
Copyright
2011,
PrismTech
–
All
Rights
Reserved.
auto dp = DomainParticipant(domainId);
Participant
Session
// Create a Topic
Publisher
Topic
Subscriber
OpenSplice DDS
auto topic = Topic<ShapeType>(dp, “Circle”);
// Create a Publisher / Subscriber
auto pub = Publisher(dp);
auto sub = Subscriber(dp);
Reader/Writers for User Defined for Types DataWriter
DataReader
// Create a DataWriter/DataWriter
auto writer = DataWriter<ShapeType>(pub, topic); Reader/Writer for
auto reader = DataReader<ShapeType>(sub, topic);
application defined
Topic Types](https://image.slidesharecdn.com/2012-11-14-advancedopensplice-part-i-cready-121205143147-phpapp01/85/Advanced-OpenSplice-Programming-Part-I-42-320.jpg)
![Anatomy of a DDS Application
[DDS C++ API 2010]
Domain
Domain
Copyright
2011,
PrismTech
–
All
Rights
Reserved.
auto dp = DomainParticipant(domainId);
Participant
Session
// Create a Topic
Publisher
Topic
Subscriber
OpenSplice DDS
auto topic = Topic<ShapeType>(dp, “Circle”);
// Create a Publisher / Subscriber
auto pub = Publisher(dp);
auto sub = Subscriber(dp);
Reader/Writers for User Defined for Types DataWriter
DataReader
// Write data
writer.write(ShapeType(“RED”, 131, 107, 89)); Reader/Writer for
// But you can also write like this...
writer << ShapeType(“RED”, 131, 107, 89);
application defined
Topic Types
// Read new data (loaned)
auto data = reader.read();](https://image.slidesharecdn.com/2012-11-14-advancedopensplice-part-i-cready-121205143147-phpapp01/85/Advanced-OpenSplice-Programming-Part-I-43-320.jpg)
![struct ShapeType {
Filters
@Key
string color;
long x;
long y;
[C++ API] };
long shapesize;
Copyright
2011,
PrismTech
–
All
Rights
Reserved.
/**
* NOTE: The Scala API if not provided with DP/Sub/Pub assumes
* default domains and default partition.
**/
// Create a Topic
auto topic = Topic<ShapeType>(dp, “Circle”);
OpenSplice DDS
// Define filter expression and parameters
auto filter = Filter(“x < 100 AND y < 200”);
// Define content filtered topic
auto cftopic =
ContentFilteredTopic<ShapeType>(“CFCircle”, topic, filter)
// Create a DataReader for the content-filtered Topic
auto dr = DataReader<ShapeType>(sub,cftopic)](https://image.slidesharecdn.com/2012-11-14-advancedopensplice-part-i-cready-121205143147-phpapp01/85/Advanced-OpenSplice-Programming-Part-I-90-320.jpg)
![struct ShapeType {
Query
@Key
string color;
long x;
long y;
[C++ API] };
long shapesize;
Copyright
2011,
PrismTech
–
All
Rights
Reserved.
// Define filter expression and parameters
auto dr = DataReader<ShapeType>(sub, topic)
OpenSplice DDS
val query = Query(dr, “x < 100 AND y < 200”);
dr.select()
.content(query)
.read();](https://image.slidesharecdn.com/2012-11-14-advancedopensplice-part-i-cready-121205143147-phpapp01/85/Advanced-OpenSplice-Programming-Part-I-91-320.jpg)
![State Selector in Action
[C++ API]
Copyright
2011,
PrismTech
–
All
Rights
Reserved.
// Read only new samples
auto data = dr.read()
// Read any samples from live instances
auto data =
dr.select()
OpenSplice DDS
.state(DataState::any_data())
.read();](https://image.slidesharecdn.com/2012-11-14-advancedopensplice-part-i-cready-121205143147-phpapp01/85/Advanced-OpenSplice-Programming-Part-I-95-320.jpg)
![Putting all Together
[C++ API]
Copyright
2011,
PrismTech
–
All
Rights
Reserved.
☐ Selectors can be composed in a flexible and expressive manner
OpenSplice DDS
auto data =
dr.select()
.content(query)
.state(data_state)
.instance(handle)
.read();](https://image.slidesharecdn.com/2012-11-14-advancedopensplice-part-i-cready-121205143147-phpapp01/85/Advanced-OpenSplice-Programming-Part-I-96-320.jpg)
Uploaded byAngelo Corsaro
Advanced OpenSplice Programming - Part I
OpenSplice DDS facilitates efficient, scalable data sharing among distributed applications and connected devices, addressing various use cases such as unmanned air vehicles and smart city systems. It operates on an active global data space model, where applications can autonomously participate and declare new data types through topics. The document details programming interactions, including defining topics, data writers, and data readers, along with how these components match dynamically in a DDS ecosystem.
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Similar to Advanced OpenSplice Programming - Part I
Advanced OpenSplice Programming - Part I
- 1. Advanced OpenSplice DDS Programming - Part I - OpenSplice DDS Angelo CORSARO, Ph.D. Chief Technology Officer OMG DDS Sig Co-Chair PrismTech angelo.corsaro@prismtech.com
- 2. Before we getinto technical details let’s try to answer two questions: Copyright 2011, PrismTech – All Rights Reserved. 1. What does OpenSplice DDS do? 2. What kind of applications are using it? OpenSplice DDS
- 3. OpenSplice DDS enablesseamless, loosely- Copyright 2011, PrismTech – All Rights Reserved. coupled, timely, scalable and dependable data sharing between distributed applications OpenSplice DDS and network connected devices.
- 4. Some Use Cases Copyright 2011, PrismTech – All Rights Reserved. OpenSplice DDS Integrated Modular Vetronics Training & Simulation Systems Naval Combat Systems Air Traffic Control & Management Unmanned Air Vehicles Aerospace Applications
- 5. Some Use Cases Copyright 2011, PrismTech – All Rights Reserved. OpenSplice DDS Agricultural Vehicle Systems Large Scale SCADA Systems Smart Cities Train Control Systems Complex Medical Devices Big Data (In-Memory) Analytics
- 6. A Fresh Lookat OpenSplice OpenSplice DDS
- 7. From Local OpenSplice DDS to Distributed Data
- 8. Data in ProgrammingLanguages Copyright 2011, PrismTech – All Rights Reserved. ☐ Statically Typed Programming Languages provide mechanisms to declare a variable for given type as well as defining new types OpenSplice DDS int x; class Rational { ... } ☐ Scoping rules are then used to define what values and types are accessible at any given point in a program text
- 9. “Local” Data ☐ Consider the Following code fragment below in an imperative programming language: Copyright 2011, PrismTech – All Rights Reserved. State 1 { 1 { } 2 int x; 2 { int x } 3 x = 7; 3 { x = 7 } OpenSplice DDS 4 { 4 { x = 7, { } } 5 int y; 5 { x = 7, { int y } } 6 y = 18; 6 { x = 7, { y = 18 } } 7 double z; 7 { x = 7, { y = 18, double z } } 8 z = 3.141593 8 { x = 7, { y = 18, z = 3.1416 } } 9 x = x -‐ 4; 9 { x = 3, { y = 2 } } 10 y = x + y; 10 { x = 3, { y = 21 } } 11 z = 2 * z * y; 11 { x = 3, { y = 21, z = 131.9472 } } 12 } 12 { x = 3, { }} 13 } 13 { }
- 10. “Local” Data ☐ One final consideration to do is that variables in a programming language are in essence alias to a memory location Copyright 2011, PrismTech – All Rights Reserved. int x; int y; OpenSplice DDS ...
- 11. Distributed Data Extending the elegant model provided by programming Copyright 2011, PrismTech – All Rights Reserved. ☐ languages to distributed systems has been and still is a quite popular research topic OpenSplice DDS ☐ Historically the solutions to the distributed data problem where divided into those based on Distributed Shared Memory and those based on Message Passing ☐ OpenSplice DDS provide a new interesting way of addressing this problem. Let’s see...
- 12.
- 13. Distributed Data inOpenSplice ☐ OpenSplice DDS provides the abstraction Copyright 2011, PrismTech – All Rights Reserved. of an “Active” Global Data Space ☐ The Global Data Space is fully distributed TopicA and does not suffer Single Point of Failure TopicE OpenSplice DDS issues TopicB ... TopicD ☐ Applications can autonomously join and TopicC leave this data space as well as declare new “Data Types” OpenSplice DDS Global Data Space ☐ In OpenSplice, “data types” are called Topics
- 14. Global Data Space ☐ The Global Data Space is actually called “Domain” in OpenSplice DDS Copyright 2011, PrismTech – All Rights Reserved. ☐ Domains are identified by integer. An application can join a domain by creating a domain participant as follows: TopicA TopicE OpenSplice DDS // Create a Topic ... int domain_id = 18; TopicB TopicD auto dp = DomainParticipant(domain_id); TopicC ☐ A Domain defines a top-level scope thus the content of a domain is not accessible from OpenSplice DDS Global Data Space another domain ☐ Finally an application can join multiple domains by creating one domain participant per-domain
- 15. Topics ☐ A Topic is defined by means of a “Circle”, Square”, “Triangle” (name, type, qos) tuple, where Copyright 2011, PrismTech – All Rights Reserved. ☐ name: identifies the topic within Name OpenSplice’s Global Data Space Topic ☐ type: is the programming language Typ S OpenSplice DDS DURABILITY, Qo type associated with the topic. This e DEADLINE, type can be defined in IDL, XML, and ShapeType PRIORITY, Java. Types are extensible and … evolvable ☐ qos: is a collection of policies that struct ShapeType { string color; control non-functional properties of long x; this topic, such as its durability, long long y; size; reliability, etc. };
- 16. Defining a Topic Copyright 2011, PrismTech – All Rights Reserved. ☐ In code, if we wanted to define the Square topic we would do (with the new DDS-PSM-Cxx v1.0 API): // Create a Topic OpenSplice DDS auto dp = DomainParticipant(18); auto topic = Topic<ShapeType>(dp, “Square”, dp.default_topic_qos()); // Or equivalently and more concisely: auto topic = Topic<ShapeType>(dp, “Square”); ☐ The effect of this code is to define a topic called “Square” with type ShapeType and default QoS within the OpenSplice Global Data Space
- 17. Looking with theSpyglass domain 18 Copyright 2011, PrismTech – All Rights Reserved. Topic Square struct&ShapeType&{ &&string&&&color;&&&&&& &&long&&&x;&&& &&long&&&y; OpenSplice DDS &&long&&&size; }; Policies auto topic = Topic<ShapeType>(dp, “Square”);
- 18. Topics Scope ☐ Topic definitions are (somewhat) equivalent to type definitions in a programming Copyright 2011, PrismTech – All Rights Reserved. language. In the sense that they define a new, generalized, type to be used within the global data space ☐ The scope of a Topic definition is the entire Domain, thus one could say that there is only one level of scoping. To make the parallel with Java, one could say OpenSplice DDS that it is as if Topics where defined in a namespace named after the domain-id domain0 {TopicA, TopicB, ...} domain1 {Topic1, Topic2, ...} ☐ As a consequence topic definitions in one domain are not visible from a different domain
- 19. If Topic areTypes what are Variables? ☐ As described earlier a Topic definition can be thought as a Type Copyright 2011, PrismTech – All Rights Reserved. definition in a programming language ☐ In a statically typed programming language (e.g. Java), given a type Foo I can define a variable of type Foo as: OpenSplice DDS Foo x; ☐ Then I can initialize it as: x = new Foo(...); ☐ Then I can mutate it, by: x.setBar(...); ☐ How are instance of a Topic defined?
- 20. DataWriter Copyright 2011, PrismTech – All Rights Reserved. ☐ OpenSplice DDS uses DataWriters to declare and write instances of a Topic ☐ A DataWriter for our Square topic can be defined as follows: OpenSplice DDS // Create a Publisher auto pub = Publisher(dp); // Create a DataWriter auto dw = DataWriter<ShapeType>(pub, topic); // Write data dw.write(ShapeType(“RED”,11,77,99));
- 21. Looking with theSpyglass Copyright 2011, PrismTech – All Rights Reserved. Topic Square struct&ShapeType&{ &&string&&&color;&&&&&& &&long&&&x;&&& &&long&&&y; OpenSplice DDS dw &&long&&&size; }; Policies color x y size auto dw = DataWriter<ShapeType>(pub, topic);
- 22. Looking with theSpyglass Copyright 2011, PrismTech – All Rights Reserved. Topic Square struct&ShapeType&{ &&string&&&color;&&&&&& &&long&&&x;&&& &&long&&&y; OpenSplice DDS dw &&long&&&size; }; Policies color x y size "RED" 11 77 99 dw.write(ShapeType(“RED”,11,77,99));
- 23. An Experiment... ☐ What does the following code do? Copyright 2011, PrismTech – All Rights Reserved. // Create a Publisher auto pub = Publisher(dp); // Create DataWriters auto dw1 = DataWriter<ShapeType>(pub, topic); OpenSplice DDS auto dw2 = DataWriter<ShapeType>(pub, topic); // Write Data dw1.write(ShapeType(“RED”,10,20,30)); dw2.write(ShapeType(“BLUE”,30,20, 10));
- 24. Looking with theSpyglass Copyright 2011, PrismTech – All Rights Reserved. Topic Square struct&ShapeType&{ &&string&&&color;&&&&&& &&long&&&x;&&& &&long&&&y; OpenSplice DDS &&long&&&size; }; dw1 Policies Data Writers for the same topic color x y size are aliased to the same variable! dw2 auto dw1 = DataWriter<ShapeType>(pub, topic); auto dw2 = DataWriter<ShapeType>(pub, topic);
- 25. Looking with theSpyglass Copyright 2011, PrismTech – All Rights Reserved. Topic Square struct&ShapeType&{ &&string&&&color;&&&&&& &&long&&&x;&&& &&long&&&y; OpenSplice DDS &&long&&&size; }; dw1 Policies color x y size RED 10 20 30 dw2 dw1.write(ShapeType(“RED”,10,20,30));
- 26. Looking with theSpyglass Copyright 2011, PrismTech – All Rights Reserved. Topic Square struct&ShapeType&{ &&string&&&color;&&&&&& &&long&&&x;&&& &&long&&&y; OpenSplice DDS &&long&&&size; }; dw1 Policies color x y size BLUE 30 20 10 dw2 dw2.write(ShapeType(“BLUE”,30,20, 10));
- 27. Topic Instances ☐ Topic type can identify an arbitrary number of attributes as defining the Copyright 2011, PrismTech – All Rights Reserved. topic key ☐ In this case, each unique key value defines a topic instance ☐ Example: OpenSplice DDS struct ShapeType { @Key long color; long x; long y; long size; };
- 28. Let’s Experiment... ☐ What does the following code do? Copyright 2011, PrismTech – All Rights Reserved. // Create a Publisher auto pub = Publisher(dp); // Create DataWriters OpenSplice DDS auto dw = DataWriter<ShapeType>(pub, topic); // Write Data dw.write(ShapeType(“RED”,10,20,30)); dw.write(ShapeType(“BLUE”,30,20,10));
- 29. Looking with theSpyglass Copyright 2011, PrismTech – All Rights Reserved. Topic Square struct&ShapeType&{ &&string&&&color;&&&&&& &&long&&&x;&&& &&long&&&y; OpenSplice DDS dw &&long&&&size; }; Policies color x y size RED 10 20 30 dw.write(ShapeType(“RED”,10,20,30));
- 30. Looking with theSpyglass Copyright 2011, PrismTech – All Rights Reserved. Topic Square struct&ShapeType&{ &&string&&&color;&&&&&& &&long&&&x;&&& &&long&&&y; OpenSplice DDS dw &&long&&&size; }; Policies color x y size RED 10 20 30 BLUE 30 20 10 dw.write(ShapeType(“BLUE”,30,20,10));
- 31. LongVariable Example ☐ The “distributed” version of the following code: Copyright 2011, PrismTech – All Rights Reserved. int x; int y; x = 10; y = 20; OpenSplice DDS Topic Type ☐ Becomes: // Create a Publisher struct LongVariable { auto lvt = Topic<LongVariable>(dp, “TLongVariable”); @Key string name; // Create DataWriters long value; auto dw = DataWriter<LongVariable>(pub, topic); }; // Write Data dw.write(LongVariable(“x”,10)); dw.write(LongVariable(“y”,20));
- 32. Looking with theSpyglass Copyright 2011, PrismTech – All Rights Reserved. Topic TLongValue struct LongVariable { @Key string name; long value; OpenSplice DDS dw }; Policies name value x 10 y 20
- 33. DataReader Copyright 2011, PrismTech – All Rights Reserved. ☐ OpenSplice DDS uses DataReaders to read instances of a Topic ☐ A DataReader for our Square topic can be defined as follows: OpenSplice DDS // Create a Subscriber auto sub = Subscriber(dp); // Create a DataWriter auto dr = DataReader<ShapeType>(sub, topic); // Read data auto data = dr.read(); ☐ The read operation will read by default all instance values. Special selector operation are available to pick a specific instance. More later
- 34. DataReader/DataWriter Matching ☐ DataWriters and DataReaders Copyright 2011, PrismTech – All Rights Reserved. are automatically and dynamically matched by the Data Reader DDS Dynamic Discovery Data Writer OpenSplice DDS Data Reader ☐ A rich set of QoS Policies Data Writer TopicA TopicD allows to control existential, TopicB Data Reader temporal, and spatial Data Writer TopicC ... properties of data and Data Data impacts DataReader/ Writer Reader DataWriter matching DDS Global Data Space
- 35.
- 36. Publishers / Subscribers Domain (e.g. Domain 123) Domain Participant Copyright 2011, PrismTech – All Rights Reserved. Topic Partition (e.g. “Telemetry”, “Shapes”, ) T1 Publisher T1 T3 Subscriber Tx OpenSplice DDS Topic Instances/Samples Ty Tb Ta DataWrter DataReader Tc Publishers and Subscribers in DDS play two roles: ☐ Coordinate actions across DataReaders/DataWriters ☐ e.g. Atomic writes across data-writers ☐ Control access to DDS partitions, a mechanism provided by DDS to further
- 37. DDS Partitions Domain Partitions DDS Publishers and Copyright 2011, PrismTech – All Rights Reserved. ☐ Subscribers can specify a M:0:0 M:0:1 M:0:2 list of regular expressions representing the partitions OpenSplice DDS to join M:1:0 M:1:1 M:1:2 ☐ Actual partition can be any string, but some M:2:0 M:2:1 M:2:2 structure can be given in order mimic hierarchy
- 38. DDS Partitions Matching Domain Partitions Copyright 2011, PrismTech – All Rights Reserved. M:0:0 M:0:1 M:0:2 M:0:* OpenSplice DDS M:1:0 M:1:1 M:1:2 M:2:0 M:2:1 M:2:2
- 39. DDS Partitions Matching Domain Partitions Copyright 2011, PrismTech – All Rights Reserved. M:0:0 M:0:1 M:0:2 OpenSplice DDS M:1:0 M:1:1 M:1:2 M:2:0 M:2:1 M:2:2 M:*:2
- 40. DDS Partitions Matching Domain Partitions Copyright 2011, PrismTech – All Rights Reserved. M:0:0 M:0:1 M:0:2 OpenSplice DDS M:1:0 M:1:1 M:1:2 M:2:0 M:2:1 M:2:2 M:0:0, M:1:1, M:2:2
- 41. Anatomy of aDDS Application OpenSplice DDS
- 42. Anatomy of aDDS Application [DDS C++ API 2010] Domain Domain Copyright 2011, PrismTech – All Rights Reserved. auto dp = DomainParticipant(domainId); Participant Session // Create a Topic Publisher Topic Subscriber OpenSplice DDS auto topic = Topic<ShapeType>(dp, “Circle”); // Create a Publisher / Subscriber auto pub = Publisher(dp); auto sub = Subscriber(dp); Reader/Writers for User Defined for Types DataWriter DataReader // Create a DataWriter/DataWriter auto writer = DataWriter<ShapeType>(pub, topic); Reader/Writer for auto reader = DataReader<ShapeType>(sub, topic); application defined Topic Types
- 43. Anatomy of aDDS Application [DDS C++ API 2010] Domain Domain Copyright 2011, PrismTech – All Rights Reserved. auto dp = DomainParticipant(domainId); Participant Session // Create a Topic Publisher Topic Subscriber OpenSplice DDS auto topic = Topic<ShapeType>(dp, “Circle”); // Create a Publisher / Subscriber auto pub = Publisher(dp); auto sub = Subscriber(dp); Reader/Writers for User Defined for Types DataWriter DataReader // Write data writer.write(ShapeType(“RED”, 131, 107, 89)); Reader/Writer for // But you can also write like this... writer << ShapeType(“RED”, 131, 107, 89); application defined Topic Types // Read new data (loaned) auto data = reader.read();
- 44.
- 45. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 46. Reader/Writer Caches write( ) Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 47. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Topic Instance Network
- 48. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 49. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Topic Instance Topic Instance Network
- 50. Reader/Writer Caches write( ) Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 51. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Writer History Network
- 52. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 53. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Reader History Reader History Network
- 54. Reader/Writer Caches write( ) Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 55. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 56. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 57. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network
- 58. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache QoS Policies ‣ History ‣ Destination Order Network ‣ Presentation ‣ Partition QoS Policies ‣ Time Based Filter ‣ Reliability ‣ Durability ‣ Ownership ‣ History ‣ Transport Priority ‣ Latency Budget ‣ Time Based Filter
- 59. Writer Cache Properties ☐ An entry for each topic instance Copyright 2011, PrismTech – All Rights Reserved. ☐ Each cache entry might contain one or more samples, the number of DataWriter samples is controlled by the History QoS Policy OpenSplice DDS ... ☐ Depending on the setting of the Durability QoS Policy, the content of the cache may be made available DataWriter Cache to late joiners. The depth of the cache controls how many samples per instance will be delivered to late joiners
- 60. Reader Cache Properties ☐ An entry for each topic instance Copyright 2011, PrismTech – All Rights Reserved. ☐ Each cache entry might contain one or more samples, the number of samples is controlled by the History QoS Policy DataReader ☐ History.KeepLast(n) keeps the last n samples OpenSplice DDS per instance ☐ History.KeepAll maintains all the samples, ... modulo resource constraints ☐ For a given instance: DataReader Cache ☐ Samples from the same writer are inserted in write-order ☐ Samples from multiple-writers are ordered using time-stamps (source or reception depending on configurable a QoS Policy)
- 61. Eventual Consistency DDS caches provide eventual consistency semantics Copyright 2011, PrismTech – All Rights Reserved. ☐ ☐ This means that a read will see the effect of a preceding write eventually OpenSplice DDS ☐ Furthermore, given a data-writer that is currently matching N readers, we can think of DDS as providing eventual consistency with W=0 and R=1 ☐ W: the number of Acks expected in order to return from a write ☐ R: the number of sources from which a read access data
- 62.
- 63. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 64. Reader/Writer Caches write( 1 ) Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 65. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 1 ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 66. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 1 ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache 1 Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 67. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 1 1 1 ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 68. Reader/Writer Caches write( 2 ) Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 1 1 1 ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 69. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 2 1 1 ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 70. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 2 1 1 ... OpenSplice DDS DataWriter Cache DataReader Cache DataReader Cache 2 Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 71. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 2 1 1 ... OpenSplice DDS 2 2 DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 72. Reader/Writer Caches write( 3 ) Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 2 1 1 ... OpenSplice DDS 2 2 DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 73. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 3 1 1 ... OpenSplice DDS 2 2 DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 74. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 3 1 1 ... OpenSplice DDS 2 2 DataWriter Cache DataReader Cache DataReader Cache 3 Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 75. Reader/Writer Caches Application Application Application Copyright 2011, PrismTech – All Rights Reserved. DataWriter DataReader DataReader 3 2 2 ... OpenSplice DDS 3 3 DataWriter Cache DataReader Cache DataReader Cache Network Assumptions: DataReader configured with history depth of 2 and DataWriter with default history depth of 1
- 76.
- 77. Dynamic View ofa Stream Copyright 2011, PrismTech – All Rights Reserved. OpenSplice DDS ... Stream: Set of samples written over time for a given topic instance.
- 78. Eventual View ofa Stream Assumptions (Default Settings): Reader History = KeepLast (1) WriterHistory = KeepLast (1) Copyright 2011, PrismTech – All Rights Reserved. Writer History Reader History ‘Past’ Samples OpenSplice DDS Stream: Set of samples written over time for a given topic instance.
- 79. Eventual View ofa Stream Assumptions: Reader History = KeepLast (n) with n > 1 WriterHistory = KeepLast (1) Copyright 2011, PrismTech – All Rights Reserved. Writer History Reader History ‘Past’ Samples OpenSplice DDS Stream: Set of samples written over time for a given topic instance.
- 80. Eventual View ofa Stream Assumptions: Reader History = KeepLast (n) with n > 1 WriterHistory = KeepLast (m) with n > m > 1 Copyright 2011, PrismTech – All Rights Reserved. Writer History Reader History ‘Past’ Samples OpenSplice DDS Stream: Set of samples written over time for a given topic instance.
- 81. Eventual View ofa Stream Assumptions: Reader History = KeepAll WriterHistory = KeepLast (m) with n > m > 1 Copyright 2011, PrismTech – All Rights Reserved. Writer History Reader History OpenSplice DDS ...
- 82. Interacting with the DataReader Cache OpenSplice DDS
- 83. Reading Data Samples ☐ Samples can be read from the Data Reader History Cache Copyright 2011, PrismTech – All Rights Reserved. ☐ The action of reading a sample is non-destructive. Samples are not removed from the cache OpenSplice DDS DataReader DataReader ... read ... DataReader Cache DataReader Cache
- 84. Taking Data Samples ☐ Samples can be taken from the Data Reader History Cache Copyright 2011, PrismTech – All Rights Reserved. ☐ The action of taking a sample is destructive. Samples are removed from the cache OpenSplice DDS DataReader DataReader ... take ... DataReader Cache DataReader Cache
- 85. Read vs. Take Copyright 2011, PrismTech – All Rights Reserved. ☐ The read operation should always be access the latest know value for topics that represent distributed state OpenSplice DDS ☐ The take operation should be used to get the last notification from a topic that represent an event
- 86.
- 87. Cherry Picking inDDS Copyright 2011, PrismTech – All Rights Reserved. ☐ DDS provides some very flexible mechanisms for selecting the data to be read: OpenSplice DDS ☐ Data Content ☐ Data Status ☐ These mechanisms are composable
- 88.
- 89. Filters and Queries Application ☐ DDS Filters allow to control what gets into a DataReader cache Copyright 2011, PrismTech – All Rights Reserved. Query ☐ DDS Queries allow to control what gets out of a DataReader cache DataReader OpenSplice DDS ☐ Filters are defined by means of ... ContentFilteredTopics ... ... ... ☐ Queries operate in conjunction with DataReader Cache read operations Filter ☐ Filters and Queries are expressed as SQL where clauses
- 90. struct ShapeType { Filters @Key string color; long x; long y; [C++ API] }; long shapesize; Copyright 2011, PrismTech – All Rights Reserved. /** * NOTE: The Scala API if not provided with DP/Sub/Pub assumes * default domains and default partition. **/ // Create a Topic auto topic = Topic<ShapeType>(dp, “Circle”); OpenSplice DDS // Define filter expression and parameters auto filter = Filter(“x < 100 AND y < 200”); // Define content filtered topic auto cftopic = ContentFilteredTopic<ShapeType>(“CFCircle”, topic, filter) // Create a DataReader for the content-filtered Topic auto dr = DataReader<ShapeType>(sub,cftopic)
- 91. struct ShapeType { Query @Key string color; long x; long y; [C++ API] }; long shapesize; Copyright 2011, PrismTech – All Rights Reserved. // Define filter expression and parameters auto dr = DataReader<ShapeType>(sub, topic) OpenSplice DDS val query = Query(dr, “x < 100 AND y < 200”); dr.select() .content(query) .read();
- 92. Instances ☐ DDS provides a very efficient way of reading data belonging to a Copyright 2011, PrismTech – All Rights Reserved. specific Topic Instance ☐ Obviously, one could use queries to match the key’s value, but this is not as efficient as the special purpose instance selector OpenSplice DDS auto handle = dr.lookup_instance(ShapeType(“RED”, 0, 0, 0)); auto data = dr.select() .instance(handle) .read();
- 93.
- 94. Sample, Instance, andView State ☐ The samples included in the DataReader cache have associated Copyright 2011, PrismTech – All Rights Reserved. some meta-information which, among other things, describes the status of the sample and its associated stream/instance ☐ The Sample State (READ, NOT_READ) allows to distinguish between OpenSplice DDS new samples and samples that have already been read ☐ The View State (NEW, NOT_NEW) allows to distinguish a new instance from an existing one ☐ The Intance State (ALIVE, NOT_ALIVE_DISPOSED, NOT_ALIVE_NO_WRITERS) allows to track the life-cycle transitions of the instance to which a sample belongs
- 95. State Selector inAction [C++ API] Copyright 2011, PrismTech – All Rights Reserved. // Read only new samples auto data = dr.read() // Read any samples from live instances auto data = dr.select() OpenSplice DDS .state(DataState::any_data()) .read();
- 96. Putting all Together [C++ API] Copyright 2011, PrismTech – All Rights Reserved. ☐ Selectors can be composed in a flexible and expressive manner OpenSplice DDS auto data = dr.select() .content(query) .state(data_state) .instance(handle) .read();
- 97. OpenSplice DDS Summing Up
- 98. Concluding Remarks OpenSplice DDS provides a very powerful abstraction for building Copyright 2011, PrismTech – All Rights Reserved. ☐ distributed applications grounded on the concept of a fully distributed global data space OpenSplice DDS ☐ Topics are used to define the types that populate the global data space while DataWriters and DataReaders are used to produce and consume values ☐ DataReaders allow very flexible data access through cache access operations
- 99.
- 100. References Copyright 2011, PrismTech – All Rights Reserved. OpenSplice | DDS Escalier ¥ #1 OMG DDS Implementation ¥ Fastest growing JVM Language ¥ Scala API for OpenSplice DDS ¥ Open Source ¥ Open Source ¥ Open Source ¥ www.opensplice.org ¥ www.scala-lang.org ¥ github.com/kydos/escalier OpenSplice DDS ¥ Simple C++ API for DDS ¥ DDS-PSM-Java for OpenSplice DDS ¥ DDS-based Advanced Distributed ¥ Open Source ¥ Open Source Algorithms Toolkit ¥ github.com/kydos/simd-cxx ¥ github.com/kydos/simd-java ¥ Open Source ¥ github.com/kydos/dada
- 101. :: Connect withUs :: ¥opensplice.com ¥forums.opensplice.org ¥@acorsaro ¥opensplice.org ¥opensplicedds@prismtech.com ¥@prismtech OpenSplice DDS ¥ crc@prismtech.com ¥sales@prismtech.com ¥youtube.com/opensplicetube ¥slideshare.net/angelo.corsaro