First experiences with CORBA

1
First experiences with CORBA

• Niko Neufeld

2
The task

• Prepare a ring display for the RICH
  reconstruction/simulation
• Want to use JAVA 2D toolkit

3
Possible strategies

• Dump data to file (from C, read with Java)
• clumsy(!), ugly(!!), synchronization(!!!)
• Link together Java and C
• difficult, huge executable, always same client
• Use a TCP socket
• elegant, client - server, standard (C)
• only primitive data types (basically bytes),
  must provide your own protocol
• CORBA
• standardized, Java and C fully supported
• free implementations available

4
CORBA / OMG

• OMG (Object Management Group)
• 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

5
CORBA intro

• 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)
• standalone, plug and playable across networks
  and platforms
• It defines services for objects
• naming, persistency, transactions etc.
• It is language/platform independent

6
CORBA - ORB

• All requests from objects to objects are handled
  by the Object Request Broker (ORB)

7
Interface Definition Language (IDL)

• IDL describes the interfaces which objects show
  to the ORB
• It contains
• modules namespaces in C
• interfaces abstract base classes in C
• operations methods
• data types standardized types
• basiccompatible to double, int, long, etc.
• constructed struct, sequence, string, any,
  union, enum
• These are mapped to the respective language types
  by the precompilers (idl, jidl)

8
IDL (trivial example)
interface Y2K const short y2k2000
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.
9
Generated IDL file
// Module Photon // Subsystem
RichDetector // 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.initialDeclaration
s preserveyes //end Photon.initialDeclaration
s // Attributes attribute double energy
attribute double thetaCherenkov //
Operations void absorbed() void
scattered(in const HepPoint3D position, in const
HepPoint3D direction) endif
10
Working with CORBA
11
How to use it

• 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!

12
What did I use?

• JAVA 1.2 on Linux
• www.blackdown.org/java-linux
• fully compliant SUN certified port of 1.2
• ORBacus 3.1.2 for C and Java
• 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)
• gcc/egcs, java

13
Some final remarks

• 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