Java 5 Language PSM for DDS: Final Submission

Java 5 PSM for DDS:
Revised Submission 2
MARS – Santa Clara, CA – December 2010

Presenter: Rick Warren, RTI
Submitting POCs:
 Rick Warren, RTI:
rick.warren@rti.com
 Angelo Corsaro, PrismTech:
angelo.corsaro@prismtech.com
document number: mars/2010-12-22

Tuesday, December 7, 2010 1

Agenda

Copyright © 2010 RTI - All rights Reserved
2

Agenda

Specification Overview
 Goals and Principles
 Process

Better Living Through Source Code
 License
 Bootstrapping
 Publishing Data
 Reading Data
 Getting and Setting QoS
 Java Type Representation

2

Goals & Design Principles

3

Improve user experience
 standardNamingConvention
 Standard containers (e.g. java.util.List)
 Standard enumerations
 Error conditions reported with exceptions
 Serializable, Cloneable value types
 Simplified method overloads

3


Improve type safety
 Generics

3


Improve type safety
 Generics

Improve performance
 Loanable memory
 No critical-path memory allocation (unlike IDL PSM)

3


Improve type safety
 Generics

Improve performance
 Loanable memory
 No critical-path memory allocation (unlike IDL PSM)

Improve portability
 Build apps against standard interfaces; decide at run time which impl to use
 Host multiple implementations (or versions) within same JVM
 Dynamic loading and unloading
 Play nicely with containers, e.g. Java EE and OSGi
 Don’t require non-constant static state
3

State of the Proposal

4

State of the Proposal

Ready for implementation
 All mandatory requirements satisfied
 User vetting process begun
 Private conversations with Java power users
 Publicly available code repository at http://
code.google.com/p/datadistrib4j/
 So far, reviewers enthusiastic

Positive AB review
 Doug Tolbert: content
 Sridhar Iyengar: license

Will ask for vote to recommend adoption
this week
4

Source Code License & Copyright

5


Principles
 Every vendor, user will receive code from OMG
 Need to know their rights
 Need free access to spec, according to OMG principles
 OMG must not dictate vendors’ business models
 Open source, shared source, closed source must be allowed
 ...under variety of licenses

5


Principles
License
 Apache 2.0 (permissive but GPL-compatible)
 Use is royalty-free, unlike BSD (proposed last time)
 Requires acknowledgement of license, copyright holders
from redistributors

5


Principles
License
 Apache 2.0 (permissive but GPL-compatible)
 Use is royalty-free, unlike BSD (proposed last time)
 Requires acknowledgement of license, copyright holders
from redistributors
Copyright
 OMG, RTI, PrismTech hold copyright
 i.e. OMG + submitters, per OMG conventions
5

Bootstrapping a DDS Java Application

6


Design pattern: API is abstract, stateless
 Interfaces when possible; stateless abstract classes when not
 Doesn’t dictate state or other implementation to vendors
Design pattern: multiple DDS’s coexist in JVM
 i.e. Even “singletons” are not
Challenge: How do you create the first object?

6


Design pattern: API is abstract, stateless
 Interfaces when possible; stateless abstract classes when not
 Doesn’t dictate state or other implementation to vendors
Design pattern: multiple DDS’s coexist in JVM
 i.e. Even “singletons” are not
Challenge: How do you create the first object?

Solution: Bootstrap class
 Represents DDS implementation
 Step 1: Bootstrap.createInstance(/*system property*/)
 Singletons: DomainParticipantFactory.getInstance(myBstrap)
 If no PIM factory: Duration.newDuration(myBstrap)
 Get back there from anywhere: myDuration.getBootstrap()
 * Note: API change since previous submission
6

Example: Publishing Data
import org.omg.dds.domain.*; import …;

// Join domain:
DomainParticipantFactory factory =
DomainParticipantFactory.getInstance(
Bootstrap.createInstance());
DomainParticipant dp =
factory.createParticipant();

// Create topic with implicit type registration:
Topic<Greeting> tp = dp.createTopic(
"My Topic",
Greeting.class);

// Create publishing entities:
Publisher pub = dp.createPublisher();
DataWriter<Greeting> dw =
pub.createDataWriter(tp);

// Publish data:
try {
dw.write(new Greeting("Hello, World"));
} catch (TimeoutException tx) {
tx.printStackTrace();
}

// Dispose of all entities:
dp.close();
7

Example: Publishing Data
import org.omg.dds.domain.*; import …;

// Join domain:
DomainParticipantFactory factory =
DomainParticipantFactory.getInstance( // Explicit TypeSupport w/ default name:
Bootstrap.createInstance()); Topic<Greeting> tp = dp.createTopic(
DomainParticipant dp = "My Topic",
factory.createParticipant(); TypeSupport.newTypeSupport(

}
Greeting.class,
// Create topic with implicit type registration: dp.getBootstrap()));
Topic<Greeting> tp = dp.createTopic(
"My Topic", // Explicit TypeSupport w/ custom name:
Greeting.class); Topic<Greeting> tp = dp.createTopic(

// Create publishing entities:
or "My Topic",
TypeSupport.newTypeSupport(
Publisher pub = dp.createPublisher(); Greeting.class,
DataWriter<Greeting> dw = "MyType",
pub.createDataWriter(tp); dp.getBootstrap()));

// Publish data:
try {
dw.write(new Greeting("Hello, World"));
} catch (TimeoutException tx) {
tx.printStackTrace();
}

// Dispose of all entities:
dp.close();
7

Example: Reading Data
...
// Create subscribing entities:
Subscriber sub = dp.createSubscriber();
DataReader<Greeting> dr = sub.createDataReader(
topic,
sub.getDefaultDataReaderQos(),
listener,
null /* all status changes */);

...

class MyListener extends DataReaderAdapter<Greeting> {
@Override
public void onDataAvailable(DataAvailableStatus<Greeting> status) {
DataReader<Greeting> dr = status.getSource();
Sample.Iterator<Greeting> it = dr.take(/* loan, or pass List to copy */);
try { while (it.hasNext()) {
Sample<Greeting> smp = it.next();
// SampleInfo stuff is built into Sample:
InstanceHandle inst = smp.getInstanceHandle();
// Data accessible from Sample; null if invalid:
Greeting dt = smp.getData();
// ...
} } finally {
it.returnLoan();
}
}
}
8

...
topic, “Listener” is interface:
listener,
implement all.
null /* all status changes */); “Adapter” is no-op
class: override what
...
you want.
@Override
// ...
} } finally {
it.returnLoan();
}
}
}
8

...
topic, “Listener” is interface:
listener,
implement all.
null /* all status changes */); “Adapter” is no-op
class: override what
...
you want.
@Override Statuses extend
java.util.EventObject
// ...
} } finally {
it.returnLoan();
}
}
}
8

Example: Get QoS

// QoS is a bean-style property of the entity:
DataReaderQos qos = myReader.getQos();

// Get specific policy:
ReliabilityQosPolicy.Kind rKind =
qos.getReliability().getKind();

// EntityQos is a Map from QosPolicy.Id to QosPolicy:
for (QosPolicy policy : qos.values()) {
// Iterate over all policies, standard or not.
// ...
}

9

Example: Set QoS

// Call modify() to get a mutable copy of the QoS:
ModifiableDataReaderQos qos = myReader.getQos().modify();

// Modifiable version provides setters:
qos.getReliability().setKind(
ReliabilityQosPolicy.Kind.RELIABLE);

// QoS setter accepts modifiable or unmodifiable objects:
myReader.setQos(qos);
myReader.setQos(myOtherReader.getQos());

10

Why the modifiable/unmodifiable pattern?

11


Easy to use correctly
 qos = entity.getQos();
Hard to get wrong
 qos = new DataReaderQos(); // ERROR!
// What state does ‘qos’ have before the next line?
entity.getQos(qos);
 What does this mean:
myDataReader.getQos().setReliability(…)

11


Easy to use correctly
 qos = entity.getQos();
Hard to get wrong
 qos = new DataReaderQos(); // ERROR!
// What state does ‘qos’ have before the next line?
entity.getQos(qos);
 What does this mean:
myDataReader.getQos().setReliability(…)
Fast to get
 Just return a pointer
 No allocation or deep copy needed
Good for concurrency
 Share immutable objects freely without locking

11

Java Type Representation

12


Goal: Write the following code:

public class MyPojo /*extends/implements…*/ {
private int foo;
private Bar[] baz;
public void doStuff() { … }
}
…
Topic<MyPojo> t = dp.createTopic(
"My Topic", MyPojo.class);

12


13


Leverage the knowledge of Java developers
Leverage the code they already have

13


Leverage the knowledge of Java developers
Leverage the code they already have

Observations:
 JRE already provides type definition constructs
 Primitive types, strings, lists (sequences), classes
(structures), enumerations, annotations
 Types to be sent over network already indicate that
 …by implementing java.io.Serializable
 …including which fields should not be sent
 …with the transient keyword

13


14


Approach: Define DDS type on the fly based
on run-time introspection of Java class

14


Approach: Define DDS type on the fly based
on run-time introspection of Java class

Convenience feature for non-real-time
Java systems
 Reflection slower than compiled generated code
 If other languages are used, type definitions must
be “duplicated”

Does not:
 ...replace, modify other Language Bindings
 ...impact serialization, therefore is interoperable

14

Java Type Representation: What It Does

15

Java Type Representation: What It Does

Defines mappings JRE concepts  DDS concepts
 int  Int32 (IDL long)
 double  Float64 (IDL double)
 java.util.List  Sequence
 Serializable class  Structure

Allows customization to support non-Java DDS
concepts
 e.g. unsigned primitives, narrow vs. wide strings, unions
 Mechanism: @SerializeAs and other annotations

15

Java Type Representation: Example

Java IDL

16


Java IDL
package com.acme; module com { module acme {

16


Java IDL

class Foo
implements Serializable { struct Foo {

16


Java IDL

class Foo
@Key int theInt; @Key long theInt;

16


Java IDL

class Foo
transient float theFlt;

16


Java IDL

class Foo
String theStr; string theStr;

16


Java IDL

class Foo
@SerializeAs(UINT_64)
BigInteger theUInt; unsigned long theUInt;

16


Java IDL

class Foo
@SerializeAs(UINT_64)
BigInteger theUInt; unsigned long theUInt;
String[] theArr; sequence<string> theArr;
} };

}}
16

Summary

Proposed specification is complete
 Provides (the first) run-time-portable API for DDS
 Improves performance over IDL-based API
 Improves type safety over IDL-based API
 Simplifies type handling
 Satisfies all mandatory requirements

We will ask for your vote on Thursday
 Vote to vote
 Vote to recommend adoption

17

Q&A

18

Appendix: Changes Since Cambridge

Changed license from BSD to Apache Simplified object creation
Modified package organization  Renamed Context to Bootstrap to avoid confusion with
JNDI
 Modifiable value type variants in parallel packages
to simplify package lists
 Reduced number of entity and condition factory
method overloads
 Moved contents of org.omg.dds.type.annotation to
org.omg.dds.type
 Pass Bootstrap as argument to factories; don’t make it
the factory for everything (required changing some
 Consolidated statuses in org.omg.dds.core.status interfaces into abstract classes)
package to match C++ proposal
 Moved built-in topic data interfaces to
Improved DDS-XTypes APIs, aligned with FTF
org.omg.dds.topic package to match C++  Simplified Dynamic Language Binding by removing
proposal unneeded methods
All new unchecked exceptions now  Improved overloads in built-in type writers
extend common base class  Fixed method names in TypeLibraryElement “union”

Improvements to value types Added JavaDoc
 All setters return enclosing object to facilitate  Added JavaDoc building to packaging script
method chaining  Included some documentation from DDS specification
 Improvements to Time and Duration (not done yet)
 Leverage TimeUnit Made some “enumerations” more extensible
 Address Y2038 problem by vendors
 Renamed Qos to EntityQos to match C++ proposal  Replaced status kind mask with collection of status
classes
 Made QosPolicy.Id an abstract class, not an
enumeration

19

Java 5 Language PSM for DDS: Final Submission

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