Corba. Corba services. The (very) global picture. Corba. Distributed Object Systems 3 CORBA/IDL. Corba. Features. Services

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1 Distributed Systems 3 CORBA/ Piet van Oostrum Sep 11, 2008 Corba Common Request Broker Architecture Middleware for communicating objects Context Management Group (OMG) Consortium of computer companies (Sun, HP, IBM,...) Defines standards (interfaces) for support of (distributed) OO applications Also for example UML Based on concrete available technology, propositions by consortium members Status Many services defined But not all implemented by all distributions yet Many commercial and open source implementations New services invented occasionally (e.g. Corba Components) Corba Corba The (very) global picture Corba services Piet van Oostrum 1 OMG To make collaboration Management go Architecture well Common Facilities Vertical Common Facilities Application s Horizontal Common Facilities Bus Services "System Frameworks" Common Facilities "Application Frameworks" Business s User Information Management Request Broker (ORB) Systems Management Task Management Naming Life Cycle Query Time Trader Licensing Events Transactions Properties Collections Security Interoperability Collaboration Persistence Externalization Concurrency Relationships Change Management The (very) global picture Common Services - Not OMG all services yetmanagement defined Architecture Piet van Oostrum 2 - Not all services yet defined Piet van Oostrum 3 Services Features Naming Referencing by name Naming schemes Events Sending events Registering interest in events Persistence Storing objects Distributed Life Cycle Systems 03/02/98 Atze Dijkstra Java RMI Creating, copying, moving, 3 deleting Dept. components of Comp.Science, on the bus UU Transactions Two-phase commit, rollback Static and dynamic method invocation Compile time or runtime definition of method invocation High-level language bindings Definition Language () Independent of language (C, C++, Smalltalk, Java, Python) Translates to language code Self-describing system Distributed Systems 03/02/98 Atze Dijkstra Java RMI 6 Dept. of Comp.Science, UU Contains information describing interfaces, methods (+ parameters), etc. a server provides Can be interrogated at runtime Many more... Piet van Oostrum 4 Piet van Oostrum 5 slides3.pdf September 11,

2 Example Quoter Looking like normal use of service Notation used: C++ int main( void ) // Use a factory to bind to any quoter Quoter_var quoter = find_quoter_service("quoter") ; const char *stock_name = "ACME ORB, Inc." ; long value = quoter->get_quote(stock_name) ; cout << stock_name << " = " << value << endl ; return 0 ; Quoter interface Functionality defined in OMG interface Quoter exception Invalid_Stock ; long get_quote( in string stock_name ) raises (Invalid_Stock) ; Description Language Used by both clients and servers Language independent With compilers to specific languages Location transparent Piet van Oostrum 6 Piet van Oostrum 7 CORBA structure Dynamic Invocation Requests Stubs Client ORB ORB Core Dynamic Skeleton Adapter identical for all ORB implementations May be multiple object adaptors Stubs and a skeleton for each object type ORB dependent interface Implementation Static Skeleton Impl CORBA core components An Request Broker (ORB) Basic or Portable Adapter (BOA/POA) An Definition Language () A Static Invocation (SII) A Dynamic Invocation (DII) A Dynamic Skeleton (DSI) and Implementation Repositories Programming language mappings An Interoperability Spec (GIOP, IIOP) GIOP (General Inter-ORB Protocol) = protocol between local ORBs IIOP (Internet Inter-ORB Protocol) = GIOP through Internet (TCP/IP) Piet van Oostrum 8 Piet van Oostrum 9 Core components Request Broker (ORB) Central component location, creation, activation Message exchange Has its own interface for local services Local ORBs + G/IIOP = object bus NB. ORB is a distributed thing, but each local part is also called ORB Usually implemented as a library inside the process (e.g. DLL or Java package) Static Invocation (SII) Client stubs (proxy pattern) Static interface to object services Dynamic Invocation (DII) is runtime variant, interface repository is used for construction of calls Core components Static skeleton Framework through which calls are passed to object service Dynamic Skeleton (DSI) is dynamic variant adapter Provides mapping of object identifiers to implementation instances Uses implementation repository identifiers ORB translates local identifier to Interoperable References (IOR) and vice-versa IOR contains all information to locate the remote object Piet van Oostrum 10 Piet van Oostrum 11 slides3.pdf September 11,

3 Adaptor Adapter Tasks of an object adapter Tasks of an object adaptor Up-call to method A skeleton Handle incoming requests Implementation ID ID B skeleton ID Adapter Broadcast services Manage object references Instantiate new objects Register new classes Impl. Basic Adapter (BOA) Basic service Barebones ORB Variety of server kinds Server kinds Single process accepting calls, blocking while handling Server per object starts at first call on object Server per method starts for each call Persistent server already exists BOA is deprecated adapter maps object ID s to object instances Skeleton maps methods names to method implementations Piet van Oostrum 12 Piet van Oostrum 13 Portable Adapter (POA) BOA is too restricted E.g. no support for moving objects or objects that are sleeping in a database. BOA is underspecified Vendors made their own extensions non-portable POA solves this Many different ways to create/revive objects Distributed Systems 03/02/98 Atze Dijkstra Java RMI 19 Dept. of Comp.Science, UU Will be treated in a later lecture. Corba implementations There are many Corba implementations: Several commercial implementations Open source implementations (see selection below) C++: TAO (The Ace ORB) OmniORB Orbit (used in Linux/Gnome) Java: built-in implementation in Java (called Java ) is not very good JacORB is a better implementation OpenORB (a bit antique) Python: Fnorb (written in Python) OmniORB Piet van Oostrum 14 Using Using 5 Create definitions 1 Client Client stubs stubs 2 Precompiler Skeletons 3 Add server impl code 4 Compile Server Server stubs stubs Instantiate Impl's Impl's 6 Adapter 7 Impl. Piet van Oostrum 15 Using From to runtime info Define object classes using Precompile file, creates stubs and skeletons Add implementation code to skeletons Compile code, creating misc interfaces and info Bind class definitions to interface repository (optional) Instantiate objects on server Register run-time objects with the implementation repository (optional) Calling Static interface as method invocation Uses normal object.method syntax Dynamic interface using special calls to construct message method invocation is constructed at run-time. Client Server Piet van Oostrum 16 Piet van Oostrum 17 slides3.pdf September 11,

4 compiler x.idl Developer We use a subset of Corba version 2 defines simple interfaces Client Developer -to-java Compiler -to-c++ Compiler Server Developer version 3 defines components can be translated to C, C++, Java, Python, etc. app.java x.java x.h x.cpp x_skel.h x_skel.cpp srv.cpp Translation generates interface definitions, stubs, skeletons, etc. Other s (e.g. Microsoft ) are similar. Java ORB Run-Time Client Executable IIOP Server Executable C++ ORB Run-Time generated file (source: Iona) Piet van Oostrum 18 Piet van Oostrum 19 concepts 1 Module: namespace, like package in Java : Basic thing, between Java interface and class Abstract interface (no objects) Local interface (only for non-remote objects) Unconstrained interface Inheritance: can inherit from one or more other interfaces (multiple inheritance): interface Dog: Pet, Animal Inherits all variables, methods, exceptions,... Unconstrained interface may not inherit from local interface All unconstrained interfaces inherit from CORBA:: (this is Corba, not Java ). Constants: const double pi= ; Operations (methods) concepts 2 Attributes (instance variables) Implemented by get/set methods Can be declared readonly (no set) Type declarations: give a name to a type typedef struct complex float re, im; typedef sequence<complex> vector; Exceptions: can have data members System exceptions: can be raised even when not specified User exceptions: must be declared with raises Standard exceptions: are defined in OMG documentation (both system and user) Piet van Oostrum 20 Piet van Oostrum 21 concepts 3 Names (identifiers) are case insensitive, so User, USER and user are the same. But you must use only one form Scopes: Names can be qualified by the module and interface in which they are defined. e.g. Stock::Quoter::get_quote If no module is used: ::Quoter::get_quote Members of structs, unions, etc. can also be qualified with the struct, etc. name Inside the same module the module part can be omitted, inside the same interface the interface part can be omitted, etc. types short 16 bit integer long 32 bit integer long long 64 bit integer signed and unsigned boolean float, double and long double fixed fixed point number char (8 bits character iso ) wchar (wide characters implementation dependent) Piet van Oostrum 22 Piet van Oostrum 23 slides3.pdf September 11,

5 types Example string strings consisting of chars wstring strings consisting of wchars octet (8 bits unchanged) namng i context struct (like in C, C++, Pascal record) union (can contain different types, chosen with a switch construction) enum (enumeration constant) array multidimensional, fixed bounds sequence array like, one-dimensional; no fixed length (max may be specified) any can contain any other type. Piet van Oostrum 24 module MyAnimals CORBA cass l with /* def of Dog */ ( mul tiple) inher itance interface Dog:Pet, Animal inst. var s,... attribut e unsigned long age; excepti on NotInterested string explanation parame ters: type void Bark(in short how_ long) and di rection raises ( NotInterested) ; method /* def of Cat */ interface Cat: Animal void Eat(); Piet van Oostrum 25 Hello Quoter module HelloApp interface Hello string sayhello(); interface HelloFactory Hello create(in string message); module Stock // An exception is a combination of // an event and maybe some data. exception Invalid_Stock ; exception Invald_Quoter ; // like C++ class, Java interface interface Quoter long get_quote(in string stock_name) raises (Invalid_Stock) ; Piet van Oostrum 26 Piet van Oostrum 27 Quoter continued Complex types in Complex types should be given a name // Manage the lifecycle of a Quoter object interface Quoter_Factory // Returns a new Quoter selected by name // e.g. "MSFT" Quoter create_quoter(in string name) raises (Invalid_Quoter); void destroy_quoter(in Quoter quoter) ; Similiar to Java constructs in, out, inout specify direction of parameters enum struct union sequence array fixed typedef typedef long int; typedef string<30> name; typedef some_complex_type mytype; Note: the name to be defined comes last!! Piet van Oostrum 28 Piet van Oostrum 29 slides3.pdf September 11,

6 Enum enum defines a series of named constants: enum Color Red, Green, Blue const Color favorite_color = Blue; module Mod enum Size small, medium, large const Mod::Size MYSIZE = Mod::medium; Error: const Color another = Mod::medium; // is an error Struct struct defines a type with a collection of fields Like a Java class without methods struct Point2D float x; float y; struct Address string<25> street; short number; string<20> city; Piet van Oostrum 30 Piet van Oostrum 31 Struct Better to use names for the complex types: In some cases this is obligatory typedef string<25> streetname; typedef string<20> cityname; struct Address streetname street; short number; cityname city; Sequence and array Arrays have fixed size and can be multidimensional: Define matrix as an array of 10*20 floats typedef double Point3D[3]; typedef float matrix[10][20]; First the type of the elements, then the name of the new type, then the dimensions!!! Sequences are onedimensional and are flexible in length They may have an upper bound typedef sequence<int> vector; typedef sequence<int, 10> bounded_vector; Piet van Oostrum 32 Piet van Oostrum 33 union union can contain any of a number of other types The choice is indicated by a discriminator This must be some integer, char, bool or enum. union message switch (char) case e : string english; case c : wstring chinese; union enum message_type SMS, struct sms_message long telephone_number; string<160> contents; struct _message string From; string To; string Subject; string contents; Piet van Oostrum 34 Piet van Oostrum 35 slides3.pdf September 11,

7 union union message switch (message_type) case SMS: sms_message sms; case _message ; to Java mapping Language mapping Most constructs map easily to Java Done by compiler Example constant, array module Example const long along = ; const long ArrayBound = 42; struct ArrayContainer long array[arraybound]; gives Piet van Oostrum 36 Piet van Oostrum 37 to Java mapping Another Example package Example; public final class along public static final int value = (int) (-12345L); public final class ArrayContainer // instance variables public int[] array; // constructors public ArrayContainer() public ArrayContainer(int[] array)... module StatMod interface Stat void init(); void additem(in double item); double getavg (); long getnum (); void getall (out double avg, out long num); Piet van Oostrum 38 Piet van Oostrum 39 Python crash course Python is an elegant dynamic programming language: No static type declarations Statements can be entered and executed directly in the interpreter High level datatypes: lists, tuples, dictionaries, classes,... Each python file is a module (namespace) and can be imported in other modules Block structure by indentation Python example class Test: #constructor, self is like this in Java def init (self, value): self.value = value def getval(self, x): return self.value, x # return a tuple x = Test(5) print x.getval(3) # should print (5, 3) instance variables/methods can only be referenced with dot notation (obj.var/obj.meth() without dot only local and global variables Piet van Oostrum 40 Piet van Oostrum 41 slides3.pdf September 11,

8 Python server part 1 Python server part 2 import sys from Fnorb.orb import BOA, CORBA import StatMod_skel class StatServer(StatMod_skel.Stat_skel): def init(self): self.count = 0 self.sum = 0.0 def getavg(self): try: return self.sum/self.count except: return 0 def getall(self): return self.getavg(),self.getnum() def additem(self, x): self.sum += x self.count += 1 def getnum(self): return self.count Piet van Oostrum 42 Piet van Oostrum 43 Python server part 3 Python server part 3 # Initialise the ORB. orb = CORBA.ORB_init(argv, CORBA.ORB_ID) # Initialise the BOA. boa = BOA.BOA_init(argv, BOA.BOA_ID) # Create an object reference ( fred is the object key). obj = boa.create( fred, StatServer._FNORB_ID) # Create an instance of the implementation class. impl = StatServer() # Write the stringified object reference to a file f = open( Server.ref, w ) f.write(orb.object_to_string(obj)) f.close() # Start the event loop. boa._fnorb_mainloop() In this example we don t use a Naming service, just write the object reference to a file. boa.obj_is_ready(obj, impl) Piet van Oostrum 44 Piet van Oostrum 45 Python client Python client import sys from Fnorb.orb import CORBA import StatMod # Initialise the ORB. orb = CORBA.ORB_init(sys.argv, CORBA.ORB_ID) # Read the server s stringified IOR from a file stringified_ior = open( Server.ref ).read() # Make sure that the server is not a nil object reference # (represented in Python by the value None). if server is None: raise Nil object reference! # Call the server! server.init() # server.additem etc. # Convert the stringified IOR into an active object reference. server = orb.string_to_object(stringified_ior) Piet van Oostrum 46 Piet van Oostrum 47 slides3.pdf September 11,

9 Java client Java client import org.omg.corba.*; import java.util.*; import java.io.*; import StatMod.*; public class StatClient public static void main(string args[]) Stat stat; String ior; try ORB orb = ORB.init(args, null); stat.init(); stat.additem(7); stat.additem(4); System.out.println(stat.getAvg()); catch (Throwable e) System.err.println(e); e.printstacktrace(system.err); BufferedReader ref = new BufferedReader (new FileReader("Server.ref")); ior = ref.readline(); stat = StatHelper.narrow (orb.string_to_object(ior)); Piet van Oostrum 48 Piet van Oostrum 49 Translation to Java Java out parameters package StatMod; public interface StatOperations void init (); void additem (double item); double getavg (); int getnum (); void getall (org.omg.corba.doubleholder avg, org.omg.corba.intholder num); IntHolder count = new IntHolder(); DoubleHolder avg = new DoubleHolder();... stat.init(); stat.additem(7); stat.additem(4); // Use out parameters stat.getall(avg, count); System.out.println(avg.value+" "+count.value); Holder classes have a value attribute that contains the actual value of the (in)out parameter. Piet van Oostrum 50 Piet van Oostrum 51 slides3.pdf September 11,