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First experiences with CORBA
Niko Neufeld
March 26, 2016
The task
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Prepare a ring display for the RICH
reconstruction/simulation
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Want to use JAVA 2D toolkit
March 26, 2016
Niko Neufeld
Possible strategies
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Dump data to file (from C++, read with Java)
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Link together Java and C++
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difficult, huge executable, always same client
Use a TCP socket
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clumsy(!), ugly(!!), synchronization(!!!)
elegant, client - server, standard (C)
only primitive data types (basically bytes),
must provide your own protocol
CORBA
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March 26, 2016
standardized, Java and C++ fully supported
free implementations available
Niko Neufeld
CORBA / OMG
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OMG (Object Management Group)
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comprises all major vendors except Microsoft
defines and develops the standard
the standard and most OMG document are available for public
download
http://www.omg.org
Microsoft has a similar approach COM/OLE
Interoperability is under way
March 26, 2016
Niko Neufeld
CORBA intro
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CORBA stands for Common Object Request
Broker Architecture
It is a standard for object/component
cooperation
A component is usually a (collection of)
object(s) which performs a well defined task
e.g. display a histogram. It is (ideally):
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It defines “services” for objects:
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standalone, “plug and play”able across networks and
platforms
naming, persistency, transactions etc.
It is language/platform independent
March 26, 2016
Niko Neufeld
CORBA - ORB
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All requests from objects to objects are
handled by the Object Request Broker (ORB)
March 26, 2016
Niko Neufeld
Interface Definition
Language (IDL)
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IDL describes the interfaces which objects
show to the ORB
It contains:
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modules = namespaces in C++
interfaces = abstract base classes in C++
operations = methods
data types = standardized types
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basic:compatible to double, int, long, etc.
 constructed: struct, sequence, string, any, union, enum
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These are mapped to the respective
language types by the precompilers (idl, jidl)
March 26, 2016
Niko Neufeld
IDL (trivial example)
interface Y2K
{
const short y2k=2000 ;
attribute short currentyear ;
exception Y2Kbug {string yeah; };
void print(in short year) raises (Y2Kbug);
};
idl y2k.idl produces y2k_skel.cpp and y2k.cpp and the header files
Not shown here (lengthy - but no need to look into them)
y2k_skel is used for the implementation of the server part and y2k.h
for a possible client.
March 26, 2016
Niko Neufeld
Generated IDL file
//## Module: Photon
//## Subsystem: Rich::Detector
//## Source file: C:\Program Files\Rational\Rational Rose 98 Evaluation Edition\Rich\Detector\Photon.idl
#ifndef Photon_idl
#define Photon_idl
#include "Rich\Detector\Pixel.idl"
interface Photon : Trajectory {
//##begin Photon.initialDeclarations preserve=yes
//##end Photon.initialDeclarations
// Attributes
attribute double energy;
attribute double thetaCherenkov;
// Operations
void absorbed();
void scattered(in const HepPoint3D &position, in const HepPoint3D &direction);
};
#endif
March 26, 2016
Niko Neufeld
Working with CORBA
March 26, 2016
Niko Neufeld
How to use it
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Server must be running somewhere
It produces a unique(!) Object reference for
the object whose service it offers
This reference can e.g. be stored as a string
and passed to a possible client
The client initializes the ORB, obtains the
object reference and gets a reference to the
object and can then call its methods
And it really works!
March 26, 2016
Niko Neufeld
What did I use?
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JAVA 1.2 on Linux
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ORBacus 3.1.2 for C++ and Java
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www.blackdown.org/java-linux
fully compliant SUN certified port of 1.2
www.ooc.com/ob/
commercial software free for non-commercial use
full CORBA IDL support, IDL to C++/Java mapping
Linux 2.0.35 (dual P2)
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March 26, 2016
gcc/egcs, java
Niko Neufeld
Some final remarks
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I started out looking for a simple solution
for C++ and Java interoperability
CORBA works very nicely, it is a very high
level way of communication
I did not check performance issues
One gets distribution, client-server, multi
language (almost) for free
There seem to be a lot more interesting
possibilities
March 26, 2016
Niko Neufeld