DDS ISO C++ PSM

ISO C++ DDS PSM

Angelo Corsaro Rick Warren
OMG DDS Co-Chair RTI
PrismTech rick.warren@rti.com

angelo.corsaro@prismtech.com

POC: Angelo Corsaro <angelo.corsaro@prismtech.com>1

Agenda
- Status Update
- Submission Scope
- API Overview
- Resource Management
- Code Example
- Type Mapping Example
- Next Steps
Copyright 2010, PrismTech / RTI

Status Update

- Tuesday 20th Sept. 2010, after a “conclave”
of 4+ hours PrismTech and RTI have
resolved all open issues and points of
divergence!
- This presentation provides a unified view of
what the joint final submission will be.


Agenda

- Status Update
- Submission Scope
- API Overview
- Code Example
- Next Steps

Submission Scope

The ISO C++ DDS PSM has the following
scope:
- Full API for DCPS v1.2 PIM
- Full API for Extensible Topics
- ISO C++ mapping of DDS Type System (as
defined in xtypes)


Key Highlights
- Simple, safe, efficient, extensible and
portable C++ API
- Well defined and safe resource management
- Use of C++ templates to ensure type safety
and improve compile time error detection
- Consistent use of Standard C++ types and
idioms, such as, std::string, std::vector,
iterators, RAII Pattern, etc., throughout the
API

API Organization
DDS type constructors.
Vendor Implementation for
the DELEGATE layer

DELEGATE

tdds idds

Standard API instantiated
from the parametrized API
dds and the vendor
implementation of the
DELEGATE layer.
ANSI/ISO C++ PSM


Resource Management
- Principles
 Safety: Never access uninitialized, freed, or
undefined state
 Determinism: Applications control when local and
remote resources are allocated and released
 Expressiveness: Maintain capabilities from PIM


Resource Management

- Expression of principles differ for
different kinds of types
 Reference types: Identity based on reference
• DDS Entities
• Wait sets and conditions
 Value types: Identity based on state
• Entity QoS and QoS policies
• Status
• Time and duration


Reference Type Usage
- Access is through smart pointers, allocated by
factory methods. These:
 Provide null initialization
 Throw exception on access to “closed” object
 May automatically manage resources
- Examples:
 Null pointer:
• Publisher pub;
• if (pub == dds::core::null) { … }
 Initialization:
• pub = dp.create_publisher();
 Copying reference:
• Publisher pub2 = pub1; —or— Publisher pub2(pub1);
// 2 references to same object
 Polymorphism & Down-Casting:
• Entity e = pub; // Publisher pub
• Publisher pub =
dds::core::polymorphic_cast<Publisher>(e);


Reference Type Mgmt

- Reference types have close() method
 Disposes object and its contained objects

- Service may automatically close objects no longer
in use
 “May” gives vendors flexibility to balance determinism,
convenience for their users
 Similar to resource management practice in JMS
 Common-sense rules:
• If I keep a reference to it, I intend to call it: still in use
• If I set a listener, I want it to call me: still in use
• If I call retain(): still in use

- Summary:
 Deterministic way to halt communication, reclaim resources
 Deterministic way to continue communication, maintain resources
 Flexibility for vendors


Agenda

- Status Update
- Submission Scope
- API Overview
- Code Example
- Next Steps

DDS Types Mapping

- The ISO C++ API is independent from the
specific mapping used for DDS Topic Types,
as far as generated types have value
semantics
 The ISO C++ API can be used with the existing
IDL2C++ type mapping, or
 It can be used with the ISO C++ mapping for
DDS Types as defined in the DDS-XTypes
specification


ISO C++ Mapping

- Main Characteristics
 Use of ISO C++ / StdLib types
 Full Attribute Encapsulation via accessors
 Container Safe

- Example... see next slide


DDS Type Mapping
DDS Topic Type ISO C++ Mapping
class TelephoneNumber {

public:
TelephoneNumber();

struct TelephoneNumber { explicit TelephoneNumber(
string prefix; const std::string& prefix,
string number; const std::string& number);
};
virtual ~TelephoneNumber()
public:
const std::string& prefix() const;
void prefix(const std::string& s);

const std::string& number() const;
void number(const std::string& s);

// State representation
// is implementation dependent
};

DDS Type Mapping
DDS Topic Type

enum MarrialStatus {
SINGLE, MARRIED, DIVORCED };

struct Person {
long age; //@id(1)
wstring name;
MarrialStatus married;
sequence<TelephoneNumber> tel;
sequence<TelefoneNumber, 2> fax;
double height; //@optional
double weight; //@optional
sequence<byte> photo; //@shared
};


DDS Type Mapping

class Person {
struct Person { public:
long age; //@id(1) int32_t age() const;
wstring name; void age(int32_t i);
MarrialStatus married; };
};


DDS Type Mapping

class Person {
struct Person { public:
long age; //@id(1) std::wstring name() const;
wstring name; void name(const std::wstring s);
MarrialStatus married; };
};


DDS Type Mapping


struct Person {
long age; //@id(1)
wstring name;
};
class Person {
public:
const std::vector<TelephoneNumber>& tel() const;
void tel(const std::vector<TelephoneNumber>& s);
};

DDS Type Mapping


struct Person {
long age; //@id(1)
wstring name;
};
class Person {
public:
const dds::core::optional<double>& height() const;
void height(double d);
void height(const dds::core::optional<double>& o);
}; Copyright 2010, PrismTech / RTI

DDS Type Mapping


struct Person {
long age; //@id(1)
wstring name;
};
class Person {
public:
std::vector<uint8_t>* photo() const;
void photo(std::vector<uint8_t>* v);
};

Code Example

DDS Topic Type
struct RadarTrack {
string id;
long x;
long y;
};


Data Writer

- Create DataWriter
using dds::core; using dds::domain;
using dds::pub; using dds::topic;

DomainId id = 0;

DomainParticipant dp =
theParticipantFactory().create_participant(id);

Publisher pub = dp.create_publisher();

Topic<RadarTrack> topic = dp.create_topic("RadarTrackTopic");
DataWriter<RadarTrack> dw = pub.create_datawriter();
RadarTrack t("T101", 100, 200);
dw.write(t);


Data Reader

using dds::core; using dds::domain;
using dds::pub; using dds::topic;

DomainId id = 0;
DomainParticipant dp(id);

DomainParticipant dp =
theParticipantFactory().create_participant();

Publisher sub = dp.create_publisher();

Topic<RadarTrack> topic = dp.create_topic("RadarTrackTopic");
DataReader<RadarTrack> reader = sub.create_datareader();


Data Reader
std::vector<RadarTrack> t;
std::vector<SampleInfo> i;

RadarTrack at[MSIZE];
SampleInfo ai[MSIZE];

- User Provided Container
dr.take(t.begin(), i.begin(), maxsize);

dr.take(at, ai, MSIZE);


Data Reader

- Loaned Data
LoanedSamples<RadarTrack> dt = dr.take();
for (LoanedSamples<RadarTrack>::Iterator it = dt.begin();
it != dt.end();
++it) {
const Sample<RadarTrack>& sample = *it;
if (sample.is_valid_data()) {
const RadarTrack& data = sample.data();
// …
}
}


Next Steps

- XTopics API
 Add support for the XTopics API
 Complete the Type Mapping to include the full
DDS-XTypes Type System

- Vote for Adoption
 December Meeting


DDS ISO C++ PSM

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