Post on 17-Dec-2015
2004-02-02 A. Ghodsi aligh@imit.kth.se 1
Common Object Request Broker Architecture
Ali Ghodsialigh@imit.kth.se
2004-02-02 A. Ghodsi aligh@imit.kth.se 2
Goal of lecture
Go a bit more into depth on the core architecture of CORBA
Less breadth Read van Steen’s book
2004-02-02 A. Ghodsi aligh@imit.kth.se 3
Reading suggestions Tanenbaum & van Steen
CORBA Section 2.3 page page 85-98 Section 3.2.2 page 152-158 Section 9.1
Read chapter 9 and compare other systems with CORBA Compare RPC and DCE Remote Objects with CORBA
Links Nice CORBA tutorial: http://www.omg.org/gettingstarted/
2004-02-02 A. Ghodsi aligh@imit.kth.se 4
Outlook General Overview
General Information Applications
Quick Architectural Overview OOP plus Distribution Transparency CORBA main overview
Interface Definition Language (IDL) Types Examples Mappings
ORB DII (and DSI) ORB interface Object Reference POA Persistent and Transient Objects
Conclusions
2004-02-02 A. Ghodsi aligh@imit.kth.se 5
General CORBA Information
Distributed Object Model (more later)
It is a middleware Difference between Network OS Middleware?
Only a standard (v 2.7, 3.0) No reference implementation! Many independent implementations
OMG - Non-profit organization 800 members! Standardized UML and more…
2004-02-02 A. Ghodsi aligh@imit.kth.se 6
Real World Applications? Support ”dinosaurs”
Companies have invested years of development in projects done in ADA, C, Smalltalk…
CORBA enables interoperability with new languages
Languages with small user-base Eg Erlang, again interoperability
Big ERM, ERP, IS Many different architectures, languages, platforms…
2004-02-02 A. Ghodsi aligh@imit.kth.se 7
Outlook General Overview Quick Architectural Overview
OOP with Distribution Transparency CORBA overview
Interface Definition Language (IDL) Types Examples Mappings
ORB Conclusions
2004-02-02 A. Ghodsi aligh@imit.kth.se 8
CORBA builds on the DOM Provides a nice model
Encapsulation
Inheritance
Polymorphism
2004-02-02 A. Ghodsi aligh@imit.kth.se 9
Exploiting Encapsulation Encapsulation enables:
Distribution Transparency Have stubs and skeletons that together with ORBs
enable distribution*.
Inter-operability** Define interfaces in a standardised way Interface Definition Language (IDL)
2004-02-02 A. Ghodsi aligh@imit.kth.se 10
Goal 1: Distribution Transparency
Encapsulation: black-box principle Has an interface Implementation details
hiddenpublic interface MathBox {
int add(int x, int y);
}
public class MathBoxCL implements MathBox {
MathBoxCL() {}
int add(int x, int y)
{ return x+y; }
}
…
MathBox obj = new MathBoxCL();
System.out.println(obj.add(10,20));
…
Transparently distribute
2004-02-02 A. Ghodsi aligh@imit.kth.se 11
Distribution Transparency
Client…
MathBox obj = new MathBoxCL();Integer result = obj.add(10,20);
…
Server Implementationint add(int x, int y) { return x+y; }
MathBoxCL (PROXY)int add(int x, int y) { Msg msg=new Msg();
msg.Marshal(x);msg.Marshal(y);SendReqMsg(HOST,IP,msg);
}
MathBoxCL (SKELETON)int invoke(msg msg){ int x, y;
x=msg.Unmarshal(INT);y=msg.Unmarshal(INT);res=serverImpl.add(x,y);Msg msg=new Msg();msg.marshal(res);SendRespMsg(HOST, IP, msg);
}
MathBoxCL (PROXY)int add(int x, int y) { Msg msg=new Msg();
msg.Marshall(x);msg.Marshall(y);SendReqMsg(HOST,IP,msg);
}
MathBoxCL (SKELETON)int invoke(msg msg) { int x, y;
x=msg.Unmarshall(INT);y=msg.Unmarshall(INT);res=serverImpl.add(x,y);Msg msg=new Msg();msg.marshall(res);SendRespMsg(HOST,IP,msg);
}
Missing parts:
• Marshalling
• Unmarshalling
• References
• Binding client to server
2004-02-02 A. Ghodsi aligh@imit.kth.se 12
Goal 2: Inter-operability
Use a language with standardized syntax to define the interface
Generate the stub and the skeleton Programming Language Independent
MathBoxCL (STUB)int add(int x, int y) { Msg msg=new Msg();
msg.Marshal(x);msg.Marshal(y);SendReqMsg(HOST,IP,msg);
}
MathBoxCL (SKELETON)int invoke(Msg msg) { int x, y;
msg=GetMsg();x=msg.Unmarshal(INT);y=msg.Unmarshal(INT);res=serverImpl.add(x,y);Msg msg=new Msg();msg.marshal(res);SendRespMsg(HOST, IP, msg);
}
JAVAC++
2004-02-02 A. Ghodsi aligh@imit.kth.se 13
Overview
STUB
Client Object Implementationoperation()
args + return value
SKELETONObject Adapter
ORB-dependent implementation
Application specific Stub and Skeleton
ORB Core ORB Core
Same inteface. ORB-independent
Network
2004-02-02 A. Ghodsi aligh@imit.kth.se 14
Outlook General Overview Architecture Overview Interface Definition Language (IDL)
Types Example Language Mappings
ORB Conclusions
2004-02-02 A. Ghodsi aligh@imit.kth.se 15
Interface Definition Language
Builds on OOP principle of encapsulation Clear boundary between implementation and interface
Independent Programming Language (Only OO?) OS Platform Network Connection etc
Can be converted to a binary format and stored in a database (i.e. well-defined schema, iterators) Interface Repository (IR) A Repository ID for each interface
2004-02-02 A. Ghodsi aligh@imit.kth.se 16
IDL’s Type System
Two levels: Interfaces for CORBA objects!
One interface per CORBA object Official types for variables
integers, floats struct, enum array string binary values …and more!
Scoped types modules exceptions Interfaces structs
2004-02-02 A. Ghodsi aligh@imit.kth.se 17
Examples
DSLABS.IDL:typedef string GroupMembers[4];
interface DS_project {long register_project(in long groupId, in string status, inout string date);
long get_status(in long groupId, out string state, out string date, out GroupMembers gm);
};
2004-02-02 A. Ghodsi aligh@imit.kth.se 18
IDL language mappings OMG defines mappings to different languages
C, C++, Java, Smalltalk, COBOL, Ada, Lisp, PL/1, Python, and IDLscript
Proprietary mappings exist for obscure languages, though not standardized!
Every ORB has an IDL compiler Creates
A STUB and A SKELETON
2004-02-02 A. Ghodsi aligh@imit.kth.se 19
Outlook General Overview Architecture Overview Interface Definition Language (IDL) ORB
DII (and DSI) ORB interface Object References POA Persistent and Transient Objects
Conclusions
2004-02-02 A. Ghodsi aligh@imit.kth.se 20
Compile time vs Runtime?
What if interfaces change? Recompile everything? Unfeasable Dynamic interface definitions required:
IS (Information Systems) ERM (Enterprise Resource Management systems) Batch Service etcetera
2004-02-02 A. Ghodsi aligh@imit.kth.se 21
Dynamic Invocation Interface (DII)
Generic run-time invocation
No compile-time knowledge of CORBA object interfaces
No stub and skeleton needed a-priori Instead, a generic interface is used
Of course defined in IDL
2004-02-02 A. Ghodsi aligh@imit.kth.se 22
Dynamic Invocation Interface (DII) cont.
In essence: Search and fetch an IDL from an Interface
Repository. (remember binary presentation of IDL)
Construct a request Specify target object, operation, and
parameters Invoke the request
C++ (not entirely true) invoke(remoteObj, ”getStatus”, paramters)
Java uses reflection/introspection (transparent): remoteObj.getStatus(paramters);
2004-02-02 A. Ghodsi aligh@imit.kth.se 23
Complete picture
StaticStub
Client Object Implementationoperation()
args + return value
StaticSkeletonDynamic
Invocation
Dynamic Skeleton Interface
Object Adapter
ORB-dependent implementation
Application specific Stub and Skeleton
ORB Core ORB Core
Same inteface. ORB-independent
Network
2004-02-02 A. Ghodsi aligh@imit.kth.se 24
Object References Remote object references
Enable clients to invoke CORBA objects
Three incarnations Language specific implementation
E.g. pointer to a stub in C++ implementing the IDL
Not valid outside local computation space Language independent ORB representation
IOR, Inter-operable Object Referenece Supported by all ORBs
Textual representation Send by e-mail, store in DB, textfiles and so on.
2004-02-02 A. Ghodsi aligh@imit.kth.se 25
Inter-operable Object References (IOR)
Remote Object Reference”Reference to an object on a serverProtocolHostname & Port
*GIOP, address, port ex: ”IIOP v1.0”,”ripper.it.kth.se”, 8765
Object Key(Adapter & Object Name)
*Which object adapter, which object?
ex: ”OA5”, ”_DSD”
Type Name(Repository ID)
Repository ID ex: ”IDL:KTH/imit/DSD:1.0”
2004-02-02 A. Ghodsi aligh@imit.kth.se 26
ORB Interface
ORBInterface
Client Object Implementationoperation()
args + return value
StaticStub
Static SkeletonDynamic
Invocation
Dynamic Skeleton Interface
Object Adapter
ORB-dependent implementation
Application specific Stub and Skeleton
ORB Core ORB Core
Same inteface. ORB-independent
Network
2004-02-02 A. Ghodsi aligh@imit.kth.se 27
ORB Interface Standard interface (defined in IDL)
All ORBs implement this interface
Important services provided: Bootstrapping, getting initial references Converting Object References to Strings and
vice versa Object Reference Counting
Distributed garbage collection
2004-02-02 A. Ghodsi aligh@imit.kth.se 28
How do I get an IOR? All ORBs implement:
string_to_object()file, e-mail, phone :)
resolve_initial_references()Returns an IOR for naming service, interface
repository Continue to search for IOR’s in a naming
service
2004-02-02 A. Ghodsi aligh@imit.kth.se 29
Portable Object Adapter (POA)
Client Object Implementationoperation()
args + return value
Object Adapter
ORB Core ORB CoreNetwork
ORBInterface
StaticStub
StaticSkeletonDynamic
Invocation
DynamicSkeletonInterface
ORB-dependent implementation
Application specific Stub and Skeleton
Same inteface. ORB-independent
2004-02-02 A. Ghodsi aligh@imit.kth.se 30
Why Object Adapters?
Several clients call the same object, what to do? Demultiplex requests
Client 1
dsObject.calculate();
Client 2
dsObject.calculate();
Server
DsObject::calculate()
{
...
}
2004-02-02 A. Ghodsi aligh@imit.kth.se 31
Why Object Adapters? (2)
Queue requests or run in separate threads? Serialize all requests One thread per object One thread per invocation Pool of threads
Client 1
dsObject.calculate();
Client 2
dsObject.calculate();
Server
DsObject::calculate()
{
...
}
2004-02-02 A. Ghodsi aligh@imit.kth.se 32
Why Object Adapters? (2)
Security between the objects? Sandboxing? Share methods, separate data?
Client 1
dsObject.calculate();
Client 2
dsObject.calculate();
Server
DsObject::calculate()
{
...
}
2004-02-02 A. Ghodsi aligh@imit.kth.se 33
Why Object Adapters? (2)
Lifespan policy: Transient objects Persistent Objects
Continues to exist even if activated/deactivated?
Client 1
dsObject.calculate();
Client 2
dsObject.calculate();
Server
DsObject::calculate()
{
...
}
2004-02-02 A. Ghodsi aligh@imit.kth.se 34
Portable Object Adapter – PL meets ORB! POA is generic and CORBA object independent
and implements different activation policies
POA keeps pointers to skeletons*
An Object Identifier is associated with object.
A table called Active Object Map maps between Object Identifers => Skeletons
2004-02-02 A. Ghodsi aligh@imit.kth.se 35
Portable Object Adapter
Server Demultiplexer
Dispatch requests
to the right POA
POA1
POA2
POA1 (policy1)
Invoke right
skeleton
Active Object Map
OBJ2 -> skel2
OBJ1 -> skel1
OBJ 1
skel1
OBJ 2
skel2
POA2(policy2)
Invoke the right
skeleton
Active Object Map
OBJ3 -> skel3
OBJ 3
skel3
2004-02-02 A. Ghodsi aligh@imit.kth.se 36
Transient Object Illustration
Stub
Object Adapter
ORB Core
Client_dsd->student_operation() Object Implementation
ORB Core
Request message
Unique ID : ”13FABCDA” ”OA5”, ”_DSD”
student_operation() + *par
Active Object Maps
OA4:
_InfoSec
OA5:
_DSC
_DSD
Skeleton
Reply message
return variables, out parameters
Unique ID : ”13FABCDA”
STUB: Object Reference
”IIOP v1.0”,”ripper”, 8765 ”OA5”, ”_DSD”IDL:Institution/IT/DSD:1.0
2004-02-02 A. Ghodsi aligh@imit.kth.se 37
Persistent Objects
A IOR to a Persistent Object always points to the same object Migration Transparency Location Transparency
Ceases to exist only if the CORBA object is logically destroyed Might move Might change IP, Port, Machine Might change POA etc
2004-02-02 A. Ghodsi aligh@imit.kth.se 38
Persistent Objects continued Its life cycle is independent of the objects
I.e. its existence is independent of whether the object is in the local address-space.
ORBs can automatically startup objects implementing persistent CORBA objects
2004-02-02 A. Ghodsi aligh@imit.kth.se 39
How is this possible? Implementation repository (IMR) is used Keeps information about
Object Adapter Startup Command Current Server
2004-02-02 A. Ghodsi aligh@imit.kth.se 40
STUB: Object Reference
”IIOP v1.0”,”IMR”, 8765 ”OA5”, ”_DSD”IDL:KTH/imit/DSD:1.0
ORB Core
Persistent Objects Illustrated
Stub
ORB Core
Client_dsd->student_operation()
Object Implementation
ORB Core
Skeleton
Implem. Repository
IMR Table
Adapter Startup Address
xOA_1 rsh x ”/bin/st” bored:131
yOA_2 /startup ir:1444
OA5 rsh ripper /run ripper:313
Active Object Maps
OA4:
_InfoSec
OA5:
_DSC
_DSD
Request message
Unique ID : ”13FABCDA” ”OA5”, ”_DSD”
student_operation() + par
”IIOP v1.0”,”ripper”, 313
Location Forward
Reply message
return variables, out parameters
Unique ID : ”13FABCDA”
2004-02-02 A. Ghodsi aligh@imit.kth.se 41
Failure and replication (IOR cont)
Protocol1Hostname1 & Port1
*GIOP, address, port ex: ”IIOP v1.0”,”ripper.it.kth.se”, 8765
Object1 Key(Adapter1 & Object1 Name)
Type Name(Repository ID)
Repository ID ex: ”IDL:KTH/imit/DSD:1.0”
HOST1/PORT2/ADAPTER2/OBJECT2 ex: ripper1/1234/oa1/obj1
HOST2/PORT2/ADAPTER2/OBJECT2 ex: ripper2/3233/oa3/obj6
…
Remote Object Reference”Reference to an object on a serverProtocol2Hostname2 & Port2
Object2 Key(Adapter2 & Object2 Name)
Multiple locations in one reference. If an invocation fails, go to next location
2004-02-02 A. Ghodsi aligh@imit.kth.se 42
Summary-1 CORBA is a standardization effort
Based on the the Distributed Object Model
Provides inter-operability
Uses proprietary interface language: IDL All CORBA objects have an interface in IDL Most of the services offered by CORBA have an
interface in IDL
2004-02-02 A. Ghodsi aligh@imit.kth.se 43
Summary-2
Provides both Dynamic and Static invocations DII/DSI and STUBS/SKELETONS
Stubs/Skeletons talk to an ORB
The ORB uses a standardized protocol to exchange Messages(Req/Resp), IORs (persistent/transient)
ORB uses a POA to implement different activation policies Threading policy Lifespan policy (Persistent vs. Transient Objects) Security (sandboxing of object implementations)
2004-02-02 A. Ghodsi aligh@imit.kth.se 44
What did I miss? A whole lot!
CORBA facilities/services Synchronization Caching Replication Fault-tolerance Security
Comparison of CORBA against .NET DCOM Java RMI etcetera
Please read chapter 9!
2004-02-02 A. Ghodsi aligh@imit.kth.se 45
The End
THANK YOU VERY MUCH!