GNOME / ORBit

Report
Components in GNOME
林咸禮
Outline
Components in GNOME
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Why object model ?
The uses of CORBA
Implementation notes
ORBit Programming
Why object model ? (1/3)
UNIX pipe system

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Allow users to create new results by joining
smaller components.
> ls | more
orbit-docs.tar.gz
orbit.zip
…
ls
pipe
More
Why object model ? (2/3)
Pipe in modern desktop environment
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The information flow is unidirectional
Characters, lines, and entire files are basic
unit of information exchange.
Not scale well with complex application
Solution
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Component based programming framework
But UNIX lacks such a framework
Why object model ? (3/3)
GNOME provides a component model
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Based on OMG’s CORBA
Adapt ORBit implementation
Object D
Object A
CORBA
Object C
Object B
The uses of CORBA in GNOME
Exporting an application’s API
General IPC and RPC mechanism
Scripting
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Automate common tasks
Define system services
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Standard interfaces
Bonobo
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Document based application
Exporting an application’s API
Export internal engine

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Use interfaces in GNOME::Gnumeric
Guppi can manipulate a spreadsheet in
gnumeric
Standard interfaces to implement
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Desktop::Editor
A mail client can choose any Editor that
implement Desktop::Editor
IPC and RPC Mechanism (1/4)
Process communication

In traditional UNIX world
 IPC: shared memory, pipe…
 RPC: TCP/IP
 IPC/RPC protocols are hand-crafted individually

Hard to maintain and too efforts on details
Program1
Hand-crafted
protocol
RPC/IPC
codes
Program2
RPC/IPC
codes
IPC / RPC
IPC and RPC Mechanism (2/4)
CORBA provide object location
transparency
Program1
Handle by
ORB
Object
referenceStub
skeleton
CORBA
Programmer’s view
Program2
Remote
Object
IPC and RPC Mechanism (3/4)
Currently use:

Communicate with embedded applications
 GNOME Control and GNOME Panel

Modify a “live” application
 Changes happen to the current server on the
fly
 Mod_CORBA apache module, Dents DNS Server)
IPC and RPC Mechanism (4/4)
embedded
program
Scripting
Allow user to automate common tasks

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Like macro and VBA in Windows
Manipulate a gnumeric spreadsheet,
automate some repetitive tasks…
Major scripting languages on UNIX have
CORBA binding

Such as Perl, Python and Java
Define system services
Many procedure carried on UNIX do not
have a standard (rely on tradition)
Use helper script is not robust
Define standard interface about system
service

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Encapsulate details by CORBA-based server
System::admin::user
System::Mail::deliver
Bonobo (1/2)
GNOME Document model
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Let document-based applications embed
themselves in each other
Similar with OLE and ActiveX in
Windows
Bonobo (2/2)
Embed many
programs in
gnumeric
Implementation notes
ORBit
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CORBA implementation on GNOME
Written in straight C, but have many language
binding
GNORBA
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Wrapper of common CORBA services in GNOME
Name server and the initialization code
 Allow to create specific application name server
 Start automatically when needed
What is CORBA (1/2)
Protocol for interaction between objects
Programmer does not care whether the
method was executed on a local
machine or remote
The ORB (Object Request Broker) will
take care of sending message between
objects
What is CORBA (2/2)
Create correct
message
Client
object
Stub
skeleton
ORB
IIOP/GIOP
ORB
Translate messages to
correct call
Interface Definition Language
Define object type
A specification language
Use idl-compiler to generate stubs and
skeletons from IDL files
C mapping
C stub
C skeleton
.idl file
Java mapping
Java stub
Java skeleton
IDL basics (1/2)
IDL modules and interfaces
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Namespace and object definition
#include and #pragma are support
IDL types
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short , unsigned short, long, long long…
IDL methods
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in, out, inout, oneway
IDL basics (2/2)
#include “orange.idl”
module FruitBasket
{
interface Apple
{
void eat_me (in boolean eat_yes_or_not);
boolean who_ate (out string who_name);
// asynchronous method
oneway boolean eaten ();
};
};
C mapping (1/2)
Language mapping
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Native representation of a CORBA-object
GNOME is almost entirely written in C
IDL C-mapping basics: methods and
attributes
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All method-calls need an object reference as first
parameter and a CORBA_Environment object as
last parameter
Mapping attribute to a _get-function and a _setfunction
C mapping (2/2)
Module FruitsBasket {
interface Apple {
void eat_me (in boolean eat_yes_or_not);
attribute boolean is_eaten;
}
}
typedef CORBA_Object FruitsBasket_Apple;
void FruitsBasket_Apple_eat_me (Fruit_Apple object,
CORBA_boolean eat_yes_or_not,
CORBA_Environment *ev);
FruitsBasket_Apple_set_is_eaten (…);
CORBA_boolean FruitsBasket_Apple_get_is_eaten (…);
The CORBA module (1/3)
Use IDL to describe all standardized objects
The ORB is a CORBA object which has IDL
interfaces
Defined in CORBA spec:
module CORBA {
…
}
module IOR {
…
}
…
The CORBA module (2/3)
CORBA::Object interface
module CORBA {
interface Object {
InterfaceDef get_interface ();
boolean is_nil ();
Object duplicate ();
void release ();
boolean is_a (in string logical_type_id);
boolean non_existant ();
boolean is_equivalent (in Object other_object);
unsigned long hash (in unsigned long maximum);
};
};
This interface is implicitly inherited by all
other interfaces
The CORBA module (3/3)
CORBA::ORB interface
module CORBA {
typedef string ORBid;
type sequence <string> arg_list;
ORB ORB_init (inout arg_list argv, in ORBid orb_ideftifier);
interface ORB {
/* serialize function */
string object_to_string (in Object obj);
Object string_to_object(in string str);
};
};
Bootstrap function of the core ORB
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CORBA::ORB_init()
Simple sample
Naming service
Use to associate each object with a
human readable string
Bind and resolve
Root
Tree structure
GNOME
servers
…
GNOME.servers.Panel
GNOME.servers.GMC
GMC
…
Panel
The POA interface (1/4)
Clients hold object references on which that
invoke methods
Server object that implements the methods
talks only to the POA
POA and the server skeleton all cooperate to
decide to which function the client request
must be passed to.
Server
Servant
POA
Servant
The POA interface (2/4)
The server registration
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Create a POA and tell the POA about its servants
Ask the POA for an object reference
Advertised to the outside world
 IOR string
 Binding this object reference to a name with the Naming
Service
IOR string
Servant
(2)
(3)
POA
(1)
Server
Servant
(3)
Naming
Service
The POA interface (3/4)
A client request 1
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Ask the Name Service about some object
reference and get a object reference
The invocation is passed to the ORB through the
stub, once the ORB find the correct server, it
hands the request to the server
(1)
Naming Service
Client
(2)
ORB
The POA interface (4/4)
A client request 2
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The ORB pass request to the server
The server then locate the POA which created the
object reference and pass the request to the POA
The request is finally passed to the correct servant
by the POA
POA
(3)
Servant
(2)
ORB
(1)
Server
Servant
CORBA in GNOME (1/2)
The Gnorba library
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Initialization
 Combine GTK+ event loop with ORBit event loop
 gnome_CORBA_init()
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Naming service
 gnome_name_service_get()
The GOAD (GNOME Object Activation
Directory)
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Find a server by its name
Add servers to the GOAD
 .gnorba files in /etc/CORBA or /urs/etc/CORBA
CORBA in GNOME (2/2)
include <orb/orbit.h>
#include <libgnorba/gnorba.h>
#include <gnome.h>
int main (int argc, char **argv)
{
CORBA_Object name_server;
CORBA_Environment ev;
CORBA_exception_init (&ev);
orb = gnome_CORBA_init ("a simple gnorba test
prgm", "v 1.0", &argc, argv, &ev);
name_server = gnome_name_service_get ();
return 0;
}
Reference
Components in the GNOME Project
GNOME & CORBA

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