CS551 Object Oriented Middleware (II) Outline. Who is the OMG?

Transcription

1 CS551 Object Oriented Middleware (II) (Chap. 4 of EDO) Yugi Lee STB #555 (816) yugi@cstp.umkc.edu 1 Outline CORBA CORBA Object Model CORBA Interface Definition Language CORBA Architecture COM Common Object Model Microsoft IDL COM Architecture RMI Java (RMI) Object Model Interface Definition in Java RMI Architecture 2 Who is the OMG? Non-profit organization with HQ in the US, representatives in United Kingdom, Germany, Japan, India, and Australia. Founded April 1989, more than 800 members. Dedicated to creating and popularizing objectoriented industry standards for application integration, e.g. CORBA ODMG-93 UML 3

2 Goal of CORBA Support distributed and heterogeneous object request in a way transparent to users and application programmers Facilitate the integration of new components with legacy components Open standard that can be used free of charge Based on wide industry consensus 4 Object Management Architecture Application Objects Domain Interfaces CORBA facilities Object Request Broker CORBAservices 5 Object Model and Interface Definition Objects Types Modules Attributes Operations Requests Exceptions Subtypes 6

3 OMG Interface Definition Language Language for expressing all concepts of the CORBA object model OMG/IDL is programming-language independent orientated towards C++ not computationally complete Different programming language bindings are available Explanation of Model and Language by Example 7 Running Example Organization #name:string 8 Club -noofmembers:int -location:address +transfer(p:player) 1 has * 1 1..* Trainer -name:string works for +train() Team -name:string coaches +bookgoalies() 1..* 1..* Player plays in -name:string Number:int +book() uses CORBA Object Model: Objects Each object has one identifier that is unique within an ORB Multiple references to objects References support location transparency Object references are persistent 9

4 CORBA Object Model: Types Constructed types typedef struct _Address { string street; string postcode; string city; } Address; Atomic types typedef sequence<address> AddressList; interface Team { Object type 10 CORBA Object Model: Modules 11 Modules module Soccer { typedef struct _Address { string street; string postcode; string city; } Address; module People { typedef struct _Address { string flat_number; string street; string postcode; string city; string country; } Address; Soccer::Address People::Address CORBA Object Model: Attributes Clients cannot change value changeable interface Player; typedef sequence<player> PlayerList; interface Trainer; typedef sequence<trainer> TrainerList; interface Team { readonly attribute string name; attribute TrainerList coached_by; attribute Club belongs_to; attribute PlayerList players; Attribute type Attribute name 12

5 CORBA Object Model: Operations Parameter kind Return types interface Team { Parameter list void bookgoalies(in Date d); string print(); Parameter type Operation name Parameter name used in requests 13 CORBA Object Model: Requests Requests are defined by client objects Request consist of Reference of server object Name of requested operation Actual request parameters Context information Request is executed synchronously Requests can be defined statically dynamically 14 CORBA Object Model: Exceptions Generic Exceptions (e.g. network down, invalid object reference, out of memory) Type-specific Exceptions Exception name Exception data exception PlayerBooked{sequence<Date> free; interface Team { void bookgoalies(in Date d) raises(playerbooked); 15 Operations declare exceptions they raise

6 CORBA Object Model: Subtypes Implicit supertype: Object Inherited by Club interface Organization { readonly attribute string name; Supertype interface Club : Organization { exception NotInClub{ readonly attribute short noofmembers; readonly attribute Address location; attribute TeamList teams; attribute TrainerList trainers; void transfer(in Player p) raises NotInClub; 16 CORBA Architecture Client Object Implementation Dynamic Invocation Client Stubs ORB Interface Implementation Skeletons Object Adapter ORB Core One standardised interface One interface per object operation One interface per object adapter ORB-dependent interface 17 Goals of COM Provide a component object model that facilitates binary encapsulation and binary compatibility Binary encapsulation: Clients do not have to be recompiled if server objects change Binary compatibility: Client and server objects can be developed with different development environments and in different languages COM is proprietary de-facto standard 18

7 Object Model and Interface Definition Interfaces Implementations and Objects Classes Attributes Operations Requests HRESULTS Inheritance 19 Microsoft IDL (MIDL) Language for expressing all COM concepts MIDL is programming-language independent evolved from OSF/RPC IDL not computationally complete Different programming language bindings are available Explanation of Model and Language by same example 20 COM Interfaces UUID Interfaces [object, uuid(1cf2b d-101b-8e b2bd118)] interface IOrganization : IUnknown { [object, Root Interface uuid(1cf2b d-101b-8e b2bd116)] interface IClub : IOrganization { Interface Inheritance 21

8 COM Implementations Implement Interface in Prog. Lang., e.g. C++ 22 #include "Soccer.h" class Player : public IPlayer { private: char* name; short Number; protected: virtual TrainerPlayer(void); TrainerPlayer(void); IMPLEMENT_UNKNOWN(TrainerPlayer) BEGIN_INTERFACE_TABLE(TrainerPlayer) IMPLEMENTS_INTERFACE(ITrainer) IMPLEMENTS_INTERFACE(IPlayer) END_INTERFACE_TABLE(TrainerPlayer) void book(); // IPlayer methods COM: Objects Instances of COM Implementations References to COM objects are called interface pointers Interface pointers refer to main memory locations References support location transparency Object references are persistent 23 COM Classes Named implementations Have one or several interfaces Are the principal mechanism to create COM objects Can return interface pointers to specific COM objects 24

9 COM Objects, Interfaces and Classes Interface uuid : GUID 1..* 1..* implements Implementation 1 instantiates 0..* Object location : int 0..* implements creates&locates Class clsid : GUID instantiates ClassObject COM: Attributes COM does support attributes Attributes must be represented as set and get operations by the designer COM has a keyword to designate this Example: interface IOrganization : IUnknown { [propget] HRESULT Name([out] BSTR val); 26 COM: Operations Parameter kind Parameter list interface IClub : IOrganization { [propget] HRESULT NoOfMembers([out] short *val); [propget] HRESULT Address([out] ADDRESS *val); [propget] HRESULT Teams([in] long cmax, [out] long *pcact, [out,size_is(cmax),length_is(*pcact)] ITeam *val); [propput] HRESULT Teams([in] long celems, [in,size_is(celems)] ITeam *val); [propget] HRESULT Trainers([out] ITrainer *val[3]); [propput] HRESULT Trainers([in] ITrainer *val[3]); HRESULT transfer([in] IPlayer *p); Return value indicating success/failure Operation name Parameter, e.g. Interface pointer 27

10 COM: HRESULTS HRESULTS are 32-bit integers Structured into four fields Severity Code Reserved Facility Code Information Code COM Operation Invocations Invocation is defined by client objects Invocation determines Interface pointer of server object Name of invoked operation Actual parameters Invocation is executed synchronously Invocation can be defined statically dynamically Clients have to interpret HRESULTS! 29 Three Implementations of Requests Client Object Method call Local Object in In-Process DLL Inter-process call with light-weight RPC Remote call with real RPC Local Object in EXE Server Object on Remote Host 30

11 COM Architecture Server Client COM Class Implementation Application Layer Object COM Proxy Interface proxy Library Object stub COM Interface stub Library Presentation Layer SCM SCM Registry Registry Microsoft RPCs OXID Object Session Layer OXID Resolver OXID Resolver 31 COM Architecture Application Layer: Client object: has a pointer to an interface proxy an implementation of the interface and a COM class (creating new instances of the implementation and locate these instances) Presentation Layer: (un)marshalling (un)marshalling interface pointers and create an interface proxy for a requested interface (object proxy, object stub) (un)marshalling and unmarshalling the parameters of all operations contained in the interface (interface proxy, interface stub) Session Layer: object activation: SCM (Service Control Manager) the mapping of interface pointers to RPC bindings and references of server objects for remote method invocation, OXID (Object Exporter Identifier) resolver 32 Goals of RMI In Java 1.0 object communication confined to objects in one Virtual Machine Remote Method Invocation (RMI) supports communication between different VMs, potentially across the network Provide tight integration with Java Minimize changes to Java language/vm Work in homogeneous environment 33

12 Java Object Model Interfaces and Remote Objects Classes Attributes Operations Exceptions Inheritance 34 Java Interfaces and Remote Objects Java already includes the concept of interfaces RMI does not have a separate interface definition language Pre-defined interface Remote Remote interfaces extend Remote Remote classes implement remote interfaces Remote objects are instances of remote classes 35 Java Remote Interface Example Package name Interface name Declare it as remote package soccer; interface Team extends Remote { String name() throws RemoteException; Trainer[] coached_by() throws RemoteException; Club belongs_to() throws RemoteException; Players[] players() throws RemoteException; void bookgoalies(date d) throws RemoteException; void print() throws RemoteException; Remote operations 36

13 Attributes 37 RMI does not attributes Attributes must be represented as set and get operations by the designer Example: interface Club extends Organization, Remote { int noofmembers() throws RemoteException; Address location() throws RemoteException; Team[] teams() throws RemoteException; Trainer[] trainers() throws RemoteException; Attribute get operations Combining Classes and Remote Interfaces interface Organization { private: String name() RemoteException; class Address { Club can return an address object String street; String postcode; String city; interface Club extends Organization, Remote { int noofmembers() throws RemoteException; Address location() throws RemoteException; Team[] teams() throws RemoteException; Trainer[] trainers() throws RemoteException; Club makes name() remotely accessible void transfer(player p) throws RemoteException; 38 Parameter Passing Atomic types are passed by value Remote objects are passed by reference Non-Remote objects are passed by value 39 class Address { String street; String postcode; String city; interface Club extends Organization, Remote { Address location() throws RemoteException; returns a copy of the address!

14 Exception Pre-Defined Exception RemoteException Type-Specific Exceptions Example: Type-specific Exception class PlayerBooked extends Exception { interface Team extends Remote { Operation declares that it may raise it void bookgoalies(date d) throws RemoteException, PlayerBooked; 40 JAVA (RMI) Architecture Client Server Stub Registry Interfaces Skeleton RMI Runtime (rmid,rmiregistry) Activation Interfaces 41 Activation in Java Stub Faulting Reference Live ref Activation ID Java VM1 2: create object in VM 3: pass object ref Java VM2 AG 1 AG 2 1: activate 4: update live ref Client Host 42 Activator Activation Descriptors: ActGroup ClassName URL Init AG 1 Team AG 2 Player AG 2 Player AG 2 Player Host

15 Key Points CORBA, COM and RMI enable objects to request operation execution from server objects on remote hosts identify server objects by object references distinguish between interface and implementation treat attributes as operations provide mechanisms to deal with failures have statically typed object models compile stubs from their IDLs support on-demand activation 43