Components in GNOME

林咸禮

Outline

Components in GNOME Why object model ? The uses of CORBA Implementation notes

ORBit Programming

Why object model ? (1/3)

UNIX pipe system Allow users to create new results by joini

ng smaller components. > ls | more

ls Morepipe

orbit-docs.tar.gzorbit.zip…

Why object model ? (2/3)

Pipe in modern desktop environment The information flow is unidirectional Characters, lines, and entire files are

basic unit of information exchange. Not scale well with complex application

Solution Component based programming

framework But UNIX lacks such a framework

Why object model ? (3/3)

GNOME provides a component model Based on OMG’s CORBA Adapt ORBit implementation

CORBAObject A

Object B

Object C

Object D

The uses of CORBA in GNOME

Exporting an application’s APIGeneral IPC and RPC mechanismScripting Automate common tasks

Define system services Standard interfaces

Bonobo Document based application

Exporting an application’s API

Export internal engine Use interfaces in GNOME::Gnumeric Guppi can manipulate a spreadsheet in g

numericStandard interfaces to implement Desktop::Editor A mail client can choose any Editor that i

mplement 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 Program2

Hand-crafted protocol

IPC / RPC

RPC/IPCcodes

RPC/IPCcodes

IPC and RPC Mechanism (2/4)

CORBA provide object location transparency

Program1 Program2

CORBA

ObjectreferenceStub

RemoteObjectskeleton

Handle by ORB

Programmer’s view

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 Like macro and VBA in Windows Manipulate a gnumeric spreadsheet, aut

omate 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 robustDefine standard interface about system service Encapsulate details by CORBA-based

server System::admin::user System::Mail::deliver

Bonobo (1/2)

GNOME Document model 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 CORBA implementation on GNOME Written in straight C, but have many language bi

ndingGNORBA 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 objectsProgrammer does not care whether the method was executed on a local machine or remoteThe ORB (Object Request Broker) will take care of sending message between objects

What is CORBA (2/2)

Client object

skeletonStub

ORB

ORB

IIOP/GIOP

Create correct message

Translate messages to correct call

Interface Definition Language

Define object typeA specification languageUse idl-compiler to generate stubs and skeletons from IDL files

.idl file

C stub

C skeleton

Java stub

Java skeleton

C mapping

Java mapping

IDL basics (1/2)

IDL modules and interfaces Namespace and object definition #include and #pragma are support

IDL types short , unsigned short, long, long long…

IDL methods 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 methodoneway boolean eaten ();

};};

C mapping (1/2)

Language mapping Native representation of a CORBA-object GNOME is almost entirely written in C

IDL C-mapping basics: methods and attributes 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 _set-function

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 objectsThe ORB is a CORBA object which has IDL interfacesDefined in CORBA spec:module CORBA {…}module IOR {…}…

The CORBA module (2/3)

CORBA::Object interfacemodule 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 CORBA::ORB_init()

Simple sample

Naming service

Use to associate each object with a human readable string Bind and resolveTree structure

…

Root

…

GNOME

servers

PanelGMC

GNOME.servers.Panel

GNOME.servers.GMC

The POA interface (1/4)

Clients hold object references on which that invoke methodsServer object that implements the methods talks only to the POAPOA and the server skeleton all cooperate to decide to which function the client request must be passed to.

POA

Servant

Servant

Server

The POA interface (2/4)The server registration 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

Servant

Servant

POA Naming Service

IOR string

(1)

(2)(3)

(3)

Server

The POA interface (3/4)A client request 1 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

ClientNaming Service

ORB

(1)

(2)

The POA interface (4/4)A client request 2 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

ORB

POA Servant

ServantServer

(1)(2)

(3)

CORBA in GNOME (1/2)

The Gnorba library Initialization

Combine GTK+ event loop with ORBit event loop gnome_CORBA_init()

Naming service gnome_name_service_get()

The GOAD (GNOME Object Activation Directory) 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 ProjectGNOME & CORBA