Java 5 PSM for DDS: Initial Submission (out of date)

Java 5 PSM for DDS:
Initial Submission
MARS – Minneapolis, MN – June 2010
Presenter: Rick Warren, RTI
Submitting POCs:
 Rick Warren, RTI:
rick.warren@rti.com
 Angelo Corsaro, PrismTech:
angelo.corsaro@prismtech.com
document number: mars/10-06-09

Agenda
Specification Overview
Specification Highlights
 Bootstrapping
 Generics
 Reading data
 QoS
TODO for the Revised Submission
Copyright © 2010 RTI - All rights Reserved 2

Goal
Improve user experience
 standardNamingConvention
 Standard containers (e.g. java.util.List)
 Standard enumerations
 Serializable value types
Improve type safety
 Generics
Improve performance
 Loanable memory
 No critical-path memory allocation

State of the Proposal
Process moving quickly and efficiently
 Submitters have already joined
 Most mandatory requirements already satisfied
 User vetting process already begun
 Private conversations with Java power users
 Publicly available code repository at
http://code.google.com/p/datadistrib4j/
 So far, reviewers enthusiastic
Still to go:
 DDS-XTypes APIs
 Java Type Representation: avoid code generation
 JavaDoc?

Design Principles
Ease of Use
 Align with standard Java technologies and conventions
 Conventional camelCase names
 Error conditions reported with exceptions
 Value types are cloneable, serializable
 Provide simplified method overloads
Performance
 Avoid critical-path memory allocation, unlike IDL PSM
Runtime Portability
 Build apps against standard interfaces; decide at runtime which
implementation to use
 Host multiple implementations (or versions) within same JVM
Dynamic Loading and Unloading
 Play nicely with containers, e.g. Java EE or OSGi
 Don’t require non-constant static state

Hello, World
import org.omg.dds.*;
Topic<Foo> t = …;
DataWriter<Foo> dw =
myPub.createDataWriter(t);
Foo data = …;
dw.write(data);
dw.close();
DataReader<Foo> dr =
mySub.createDataReader(t);
Sample.Iterator<Foo> it =
dr.take();
Foo data2 = it.next().
getData();
it.returnLoan();
dr.close();
 OMG package
 Typical naming
convention
 Overloaded
methods
 Generics for type
safety
 Close like JMS,
I/O stream
 Standard
collections

Highlight: Bootstrapping
Design pattern: Everything is an interface (if
possible) or abstract class (if not).
Challenge: How do you create the first object?
JMS answer: JNDI
import javax.naming.*;
import javax.jms.*;
Context ctx = new InitialContext();
Topic t = (Topic) ctx.lookup("My Topic");

DDS complications with lookup:
 Lots of “top-level” objects
 DomainParticipantFactory
 WaitSet, GuardCondition
 Statuses
 Time, duration
 …
 DDS is more dynamic
 Create topics on the fly
 WaitSet is not logically an “administered object”

Solution: JNDI-like DDS Context
Create reflectively based on system property:
 org.omg.dds.core.Context ctx =
Context.getInstance(
/* "org.omg.dds.serviceClassName" */);
Create everything else from here:
 DomainParticipantFactory dpf =
ctx.getParticipantFactory();
 Duration duration = ctx.createDuration();
Get back here from anywhere:
 Context ctx = duration.getContext();

Highlight: Generics
Design pattern: Use generic types wherever they
help polymorphic type safety
Obvious:
DataWriter<Foo> dw = …;
Non-obvious:
interface Entity<SELF extends Entity,
LISTENER extends
EventListener,
QOS extends Qos> {
LISTENER getListener();
QOS getQos();
StatusCondition<SELF> getStatusCondition();
}

Highlight: Generics
Example type:
interface DataWriter<TYPE>
extends Entity<DataWriter<TYPE>,
DataWriterListener<TYPE>,
DataWriterQos>
Example uses:
void closeTheEntity(Entity<?, ?, ?> e) {
e.close();
}
<LS> void setTheListener(Entity<?, LS, ?> e, LS ln) {
e.setListener(ln);
}

Highlight: Reading Data
Take a loan:
Sample.Iterator<Foo> it = reader.take();
try {
while (it.hasNext()) {
Sample<Foo> spl = it.next();
InstanceHandle hdl = spl.getInstanceHandle();
Foo data = spl.getData();
if (data != null) {
// ...
}
}
} finally {
it.returnLoan();
}

Highlight: Reading Data
Take a copy:
List<Sample<Foo>> dataList =
new ArrayList<Sample<Foo>>();
reader.take(dataList);
for (Iterator<Sample<Foo>> it = dataList.iterator();
it.hasNext();) {
Sample<Foo> spl = it.next();
InstanceHandle hdl = spl.getInstanceHandle();
Foo data = spl.getData();
if (data != null) {
// ...
}
}

Highlight: QoS
Typical Bean property:
 Qos getQos();
 void setQos(Qos q);
By default, QoS are immutable
 Getters: myQos.getReliability();
 No setters: myQos.setReliability(…);
QoS are also Maps:
 java.util.Map<QosPolicy.Id, QosPolicy> map = myQos;
 ReliabilityQosPolicy p = (ReliabilityQosPolicy) map.get(
QosPolicy.Id.RELIABILITY);
Modify explicitly:
 ModifiableQos mod = myQos.modify(); // new obj
 mod.setReliability(myReliability);
 myEntity.setQos(mod); // mod interface extends unmod

Highlight: QoS
Why the modifiable/unmodifiable pattern?
 Easy to use: Bean property
 Conventional, intuitive
 Works as expected with introspection
 Good for concurrency: immutable object freely shared
 “Get” is fast: just return pointer
 No memory allocation needed
 No deep copy needed
Cost: “Set” must allocate new object (for next “get”)
 …but “set” is slow anyway:
 Deeply copies QoS
 Sends update on built-in topic
 …and setQos is not typically a critical-path operation
 RTSJ users must be aware

Highlight: QoS
Alternative (discarded) design
with modifiable QoS (à la IDL PSM):
DataWriterQos qos =
ctx.createDataWriterQos();
 Requires additional factory methods
ReliabilityQosPolicy.Kind k =
qos.getReliability().getKind();
 Value of “k” is undefined
myWriter.getQos(qos);
 Unintuitive signature
qos.getReliability().setKind(…);
 Object “qos” can’t be safely stored, shared

Revised Submission TODO
New DDS-XTypes APIs
 Built-in types: String, Bytes, KeyedString, KeyedBytes
 Dynamic Language Binding: DynamicType, DynamicData
 TypeObject Type Representation
 New QoS policies
Java Type Representation
@DdsType interface Employee {
@Key int getEmployeeIdNumber();
}

Revised Submission TODO
Copy specification into JavaDoc?
 Friendly for IDE users
 myWriter.setQos|
Examples (non-normative)
 Application code example
 No-op reference implementation
Further community review
void setQos(DataWriterQos q)
Set the QoS of this DataWriter. The result
of subsequent calls to getQos will be
equal to the value set by this method.

Summary
DDS will have a first-class
Java API.
 That looks and behaves like a
typical Java API.
 That performs well.
 Soon.

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Java 5 PSM for DDS: Initial Submission (out of date)

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