CORBA Programming with TAOX11/C++11 tutorial

CORBA Programming
with
TAOX11
The C++11 CORBA Implementation

TAOX11: the CORBA
Implementation by Remedy IT
TAOX11 simplifies development of CORBA based
applications
IDL to C++11 language mapping is easy to use
Greatly reduces the CORBA learning curve
Reduces common user mistakes
Improves application stability and reliability
Significant improvement of run-time performance
CORBA AMI support
Extended suite of unit tests and examples
Copyright © Remedy IT2

TAOX11
Commercial CORBA implementation by Remedy IT
Compliant with the OMG IDL to C++11 language
mapping
IDL compiler with front end supporting IDL2, IDL3,
and IDL3+
Free evaluation versions available from our software
support portal !
More details on http://taox11.remedy.nl
3 Copyright © Remedy IT

Tutorial overview
This tutorial gives an overview of the IDL to C++11
language mapping
Introduces TAOX11, the C++11 CORBA
implementation by Remedy IT
It assumes basic understanding of IDL and CORBA

Introduction

Problems with IDL to C++
The IDL to C++ language mapping is from the 90’s
IDL to C++ could not depend on various C++ features
as
• C++ namespace
• C++ exceptions
• Standard Template Library
As a result the IDL to C++ language mapping
• Is hard to use correctly
• Uses its own constructs for everything

Why a new language mapping?
IDL to C++ language mapping is impossible to
change because
• Multiple implementations are on the market (open
source and commercial)
• A huge amount of applications have been developed
An updated IDL to C++ language mapping would
force all vendors and users to update their products
The standardization of a new C++ revision in 2011
(ISO/IEC 14882:2011, called C++11) gives the
opportunity to define a new language mapping
• C++11 features are not backward compatible with
C++03 or C++99
• A new C++11 mapping leaves the existing mapping
intact

Goals of IDL to C++11
Simplify mapping for C++
Make use of the new C++11 features to
• Reduce amount of application code
• Reduce amount of possible errors made
• Gain runtime performance
• Speedup development and testing
Faster time to market
Reduced costs
Reduced training time

OMG Specification
IDL to C++11 v1.2 available from the OMG website
as formal/2015-08-01
Revision Task Force (RTF) is active to work on
issues reported

IDL Constructs

Modules
An IDL module maps to a C++ namespace with the
same name
module M
{
// definitions
};
module A
{
module B
{
// definitions
};
};
IDL C++11
namespace M
{
// definitions
};
namespace A
{
namespace B
{
// definitions
};
};

Basic Types
IDL C++11 Default value
short int16_t 0
long int32_t 0
long long int64_t 0
unsigned short uint16_t 0
unsigned long uint32_t 0
unsigned long long uint64_t 0
float float 0.0
double double 0.0
long double long double 0.0
char char 0
wchar wchar_t 0
boolean bool false
octet uint8_t 0

Constants
IDL constants are mapped to C++11 constants
using constexpr when possible
const string name = "testing";
interface A
{
const float value = 6.23;
};
IDL C++11
const std::string name {"testing"};
class A
{
public:
static constexpr float value {6.23F};
};

String Types
No need to introduce an IDL specific type
mapping but leverage STL
string name;
wstring w_name;
IDL C++11
std::string name {“Hello”};
std::wstring w_name;
std::cout << name << std::endl;

Enumerations
IDL enums map to C++11 strongly typed enums
enum Color
{
red,
green,
blue
};
IDL C++11
enum class Color : uint32_t
{
red,
green,
blue
};
Color mycolor {Color::red};
if (mycolor == Color::red)
{
std::cout << “Correct color”;
}
else
{
std::cerr << “Incorrect color “ <<
mycolor << std::endl;
}

Sequence
IDL unbounded sequence maps to std::vector
typedef sequence<long> LongSeq;
typedef sequence<LongSeq, 3> LongSeqSeq;
IDL C++11
typedef std::vector <int32_t> LongSeq;
typedef std::vector <LongSeq> LongSeqSeq;
LongSeq mysequence;
// Add an element to the vector
mysequence.push_back (5);
// Dump using C++11 range based for loop
for (const int32_t& e : mysequence)
{
std::cout << e << “;” << std::end;
}

Struct (1)
IDL struct maps to a C++ class with copy and move
constructors/assignment operators and accessors
struct Variable {
string name;
};
IDL C++11
class Variable
{
public:
Variable ();
~Variable ();
Variable (const Variable&);
Variable (Variable&&);
Variable& operator= (const Variable& x);
Variable& operator= (Variable&& x);
explicit Variable (std::string name);
void name (const std::string& _name);
void name (std::string&& _name);
const std::string& name () const;
std::string& name ();
};
namespace std
{
template <>
void swap (Variable& m1, Variable& m2);
};

Struct (2)
IDL struct maps to a C++ class with copy and move
constructors/assignment operators and accessors
struct Variable {
string name;
};
IDL C++11
Variable v;
Variable v2 (“Hello”);
std::string myname {“Hello”};
// Set a struct member
v.name (myname);
// Get a struct member
std::cout << “name” << v.name () <<
std::endl;
if (v != v2)
{
std::cerr << “names are different”
<<std::endl;
}

Array
IDL array map to C++11 std::array
typedef long L[10];
typedef string V[10];
typedef string M[1][2][3];
IDL C++11
typedef std::array <int32_t, 10> L;
typedef std::array <std::string, 10> V;
typedef std::array <std::array <std::array
<std::string, 3>, 2>, 1> M;
// Initialize the array
F f = { {1, 2, 3, 4, 5} }
// Check the size of an array
if (f.size () != 5)

Reference Types (1)
An IDL interface maps to so called reference types
Reference types are reference counted, for example
given type A
• Strong reference type behaves like
std::shared_ptr and is available as
IDL::traits<A>::ref_type
• Weak reference type behaves like std::weak_ptr
and is available as
IDL::traits<A>::weak_ref_type
A nil reference type is represented as nullptr
Invoking an operation on a nil reference results in a
INV_OBJREF exception

Reference Types (2)
Given IDL type A the mapping delivers
IDL::traits<A> with type traits
interface A
{
// definitions
};
IDL C++11
// Obtain a reference
IDL::traits<A>::ref_type a = // .. obtain a
// reference
// Obtain a weak reference
IDL::traits<A>::weak_ref_type w =
a.weak_reference();
// Obtain a strong reference from a weak one
IDL::traits<A>::ref_type p = w.lock ();
if (a == nullptr) // Legal comparisons
if (a != nullptr ) // legal comparison
if (a) // legal usage, true if a != nullptr
if (!a) // legal usage, true if a == nullptr
if (a == 0) // illegal, results in a compile
// error
delete a; // illegal, results in a compile error

Reference Types (3)
Reference types can only be constructed using
CORBA::make_reference
interface A
{
// definitions
};
IDL C++11
// Servant implementation class
class A_impl final : public
CORBA::servant_traits<A>::base_type
{
}
// Create a servant reference using
// make_reference
CORBA::servant_traits<A>::ref_type a_ref =
CORBA::make_reference<A_impl> ();
// We could use new, but the resulting
// pointer can’t be used for making any
// CORBA call because the pointer can’t be
// used to construct a reference type which
// is the only thing the API accepts
A_impl* p = new ACE_impl ();
// Or we can obtain a reference from another
// method
IDL::traits<A>::ref_type = foo->get_a ();

Reference Types (4)
Widening and narrowing references
interface A
{
// definitions
};
interface B : A
{
// definitions
};
IDL C++11
IDL::traits<B>::ref_type bp = ...
// Implicit widening
IDL::traits<A>::ref_type ap = bp;
IDL::traits<Object>::ref_type objp = bp;
objp = ap;
// Explicit narrowing
bp = IDL::traits<B>::narrow (ap)

Argument Passing
Simplified rules for argument passing compared to
IDL to C++
No need for new/delete when passing arguments
The C++11 move semantics can be used to prevent
copying of data
Given an argument of A of type P:
• In: for all primitive types, enums, and reference
types, the argument is passed as P. For all other
types, the argument is passed as const P&
• Inout: passed as P&
• Out: passed as P&
• Return type: returned as P

IDL Traits
For each IDL type a IDL::traits<> specialization
will be provided
The IDL traits contain a set of members with meta
information for the specific IDL type
The IDL traits are especially useful for template meta
programming

Implement Interfaces
Given a local interface A the implementation has to
be derived from IDL::traits<A>::base_type
Given a regular interface A the CORBA servant
implementation has to be derived from
CORBA::servant_traits<A>::base_type
In both cases a client reference is available as
IDL::traits<A>::ref_type

CORBA AMI
TAOX11 has support for the callback CORBA AMI
support
The TAO AMI implementation has the disadvantage
that when AMI is enabled for an IDL file all users
have to include the TAO Messaging library
TAOX11 separates CORBA AMI into a new set of
source files, a client not needing AMI doesn’t have to
link any CORBA Messaging support!
All sendc_ operations are member of a derived
CORBA AMI stub, not part of the regular
synchronous stub

CORBA AMI Traits
Instead of remembering some specific naming rules
a new CORBA::amic_traits<> trait has been
defined
Contains the concrete types as members
• replyhandler_base_type: the base type for
implementing the reply handler servant
• replyhandler_servant_ref_type: the type for
a reference to the servant of the reply handler
• ref_type: the client reference to the stub with all
synchronous operations

CORBA AMI Example
// Obtain a regular object reference from somewhere, Test::A has one method called foo
IDL::traits<Test::A>::ref_type stub = …;
// Narrow the regular object reference to the CORBA AMI stub (assuming this has been
// enabled during code generation
CORBA::amic_traits<Test::A>::ref_type async_stub =
CORBA::amic_traits<Test::A>::narrow (stub);
// Assume we have a Handler class as reply handler implemented, create it and
// register this as CORBA servant
CORBA::amic_traits<Test::A>::replyhandler_servant_ref_type h =
CORBA::make_reference<Handler> ();
PortableServer::ObjectId id =
root_poa->activate_object (h);
IDL::traits<CORBA::Object>::ref_type handler_ref =
root_poa->id_to_reference (id);
CORBA::amic_traits<Test::A>::replyhandler_ref_type test_handler =
CORBA::amic_traits<Test::A>::replyhandler_traits:::narrow (handler_ref);
// Invoke an asynchronous operation, can only be done on async_stub, not on stub
async_stub->sendc_foo (test_handler, 12);
// But we can also invoke a synchronous call
async_stub->foo (12);

Valuetypes
Valuetypes are mapped to a set of classes which are
accessible through the IDL::traits<>
• IDL::traits<>::base_type provides the
abstract base class from which the valuetype
implementation could be derived from
• IDL::traits<>::obv_type provides the object
by value class that implements already all state
accessors and from which the valuetype
implementation can be derived from
• IDL::traits<>::factory_type provides base
class for the valuetype factory implementation

Example CORBA application

CORBA Hello world
interface Hello
{
/// Return a simple string
string get_string ();
/// A method to shutdown the server
oneway void shutdown ();
};
IDL

CORBA client
int main(int argc, char* argv[])
{
try
{
// Obtain the ORB
IDL::traits<CORBA::ORB>::ref_type orb = CORBA::ORB_init (argc, argv);
// Create the object reference
IDL::traits<CORBA::Object>::ref_type obj = orb->string_to_object ("file://test.ior");
// Narrow it to the needed type
IDL::traits<Test::Hello>::ref_type hello = IDL::traits<Test::Hello>::narrow (obj);
// Invoke a method, invoking on a nil reference will result in an exception
std::cout << "hello->get_string () returned " << hello->get_string () << std::endl;
// Shutdown the server
hello->shutdown ();
// Cleanup our ORB
orb->destroy ();
}
catch (const std::exception& e)
{
// All exceptions are derived from std::exception
std::cerr << "exception caught: " << e.what () << std::endl;
}
return 0;
}

CORBA servant
C++11 CORBA servant for type T must be derived
from CORBA::servant_traits<T>::base_type
class Hello final : public CORBA::servant_traits<Test::Hello>::base_type
{
public:
// Constructor
Hello (IDL::traits<CORBA::ORB>::ref_type orb) : orb_ (orb) {}
// Destructor
virtual ~Hello () {}
// Implement pure virtual methods from the base_type
virtual std::string get_string () override
{
return “Hello!”;
}
virtual void shutdown () override
{
this->orb_->shutdown (false);
}
private:
// Use an ORB reference to shutdown the application.
IDL::traits<CORBA::ORB>::ref_type orb_;
};

CORBA server (1)
{
try
{
// Obtain our ORB
IDL::traits<CORBA::ORB>::ref_type orb = CORBA::ORB_init (argc, argv);
// Obtain our POA and POAManager
IDL::traits<CORBA::Object>::ref_type obj = orb->resolve_initial_references ("RootPOA");
IDL::traits<PortableServer::POA>::ref_type root_poa =
IDL::traits<PortableServer::POA>::narrow (obj);
IDL::traits<PortableServer::POAManager>::ref_type poaman = root_poa->the_POAManager ();
// Create the servant
CORBA::servant_traits<Test::Hello>::ref_type hello_impl =
CORBA::make_reference<Hello> (orb);
// Activate the servant as CORBA object
PortableServer::ObjectId id = root_poa->activate_object (hello_impl);
IDL::traits<CORBA::Object>::ref_type hello_obj = root_poa->id_to_reference (id);
IDL::traits<Test::Hello>::ref_type hello =
IDL::traits<Test::Hello>::narrow (hello_obj);
// Put the IOR on disk
std::string ior = orb->object_to_string (hello);
std::ofstream fos("test.ior");
fos << ior;
fos.close ();

CORBA server (2)
// Activate our POA
poaman->activate ();
// And run the ORB, this method will return at the moment the ORB has been shutdown
orb->run ();
// Cleanup our resources
root_poa->destroy (true, true);
orb->destroy ();
}
{
// Any exception will be caught here
}
return 0;
}

Auto specifier
C++11 has support for auto as new type specifier
The compiler will deduce the type of a variable
automatically from its initializers
Will simplify the CORBA example further

CORBA client
{
try
{
// Obtain the ORB
auto orb = CORBA::ORB_init (argc, argv);
// Create the object reference
auto obj = orb->string_to_object ("file://test.ior");
// Narrow it to the needed type
auto hello = IDL::traits<Test::Hello>::narrow (obj);
// Invoke a method, invoking on a nil reference will result in an exception
std::cout << "hello->get_string () returned " << hello->get_string () << std::endl;
// Shutdown the server
hello->shutdown ();
// Cleanup our ORB
orb->destroy ();
}
{
// All exceptions are derived from std::exception
}
return 0;
}

CORBA servant
C++11 CORBA servant for type T must be derived
from CORBA::servant_traits<T>::base_type
class Hello final : public CORBA::servant_traits<Test::Hello>::base_type
{
public:
// Constructor
Hello (IDL::traits<CORBA::ORB>::ref_type orb) : orb_ (orb) {}
// Destructor
virtual ~Hello () {}
// Implement pure virtual methods from the base_type
virtual std::string get_string () override
{
return “Hello!”;
}
virtual void shutdown () override
{
this->orb_->shutdown (false);
}
private:
// Use an ORB reference to shutdown the application.
IDL::traits<CORBA::ORB>::ref_type orb_;
};

CORBA server (1)
{
try
{
// Obtain our ORB
auto _orb = CORBA::ORB_init (argc, argv);
// Obtain our POA and POAManager
auto obj = _orb->resolve_initial_references ("RootPOA");
auto root_poa = IDL::traits<PortableServer::POA>::narrow (obj);
auto poaman = root_poa->the_POAManager ();
// Create the servant
auto hello_impl = CORBA::make_reference<Hello> (orb);
// Activate the servant as CORBA object
auto id = root_poa->activate_object (hello_impl);
auto hello_obj = root_poa->id_to_reference (id);
auto hello = IDL::traits<Test::Hello>::narrow (hello_obj);
// Put the IOR on disk
auto ior = orb->object_to_string (hello);
std::ofstream fos("test.ior");
fos << ior;
fos.close ();

CORBA server (2)
// Activate our POA
poaman->activate ();
// And run the ORB, this method will return at the moment the ORB has been shutdown
orb->run ();
// Cleanup our resources
root_poa->destroy (true, true);
orb->destroy ();
}
{
// Any exception will be caught here
}
return 0;
}

Tips & Tricks
Don’t use new/delete
Use pass by value together with C++11 move
semantics

Conclusion
C++11 simplifies CORBA programming
The combination of reference counting and C++11
move semantics make the code much safer and
secure
Application code is much smaller and easier to read

Want to know more?
Look at the TAOX11 website at
http://taox11.remedy.nl
Check the Remedy IT provided examples at
https://github.com/RemedyIT/idl2cpp11
Request your free-of-charge evaluation license, see
http://swsupport.remedy.nl
Contact us, see http://www.remedy.nl

Contact
Remedy IT
Postbus 81
6930 AB Westervoort
The Netherlands
tel.: +31(0)88 053 0000
e-mail: sales@remedy.nl
website: www.remedy.nl
Twitter: @RemedyIT
Slideshare: RemedyIT
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