1 Pass-By-Value Services in Object Component Software Group 1 Yannick Loitiere Andrea Rowan Michele Co Jinze Liu

2 Object Component Software Middleware with abstraction –Implementation separated from interface “Client” and “server” share objects –Across a network –Between different programming languages Popular software –OMG CORBA (Common Object Request Broker Architecture) –Microsoft COM (Component Object Model) –Java

3 Object Passing Pass-By-Reference –Server returns reference to the object –Client calls the server with the reference –Server executes methods and returns the value Pass-By-Value –Server returns copy, reference to local copy –Client calls the local copy with the reference –Client executes method and returns the value

4 Bank Example Account –Name Object (immutable) –Balance Object (mutable) Pass-By-Reference –Consistency for Balance Object –Performance hurt for Name Object Pass-By-Value –Inconsistency for Balance Object –Performance gains for Name Object

5 Related Work Ennio Grasso’s Model –Consistency maintained –All objects CORBA objects CORBA 2.3 OBV Model –No consistency –Separate ValueBase objects

6 Our Project Analyze CORBA's Object By Value (OBV) service using TAO Identify problems with the current implementation of pass-by-value Measure performance differences for different pass-by-value models Propose a better model of pass-by-value –Identify limitations of our pass-by-value service

7 Evaluation of Models Consistency Orthogonality / Semantics Client Control Language Transparency Location Transparency Performance

8 Consistency

9 Orthogonality/Semantics TAO separates ValueBase objects from CORBA objects Amount of pass-by-value specific code in our simple client/server program: –2/6 lines of the interface –11/88 lines from the server-side code –1/59 lines from the client-side code –Represents 9.15% of all code

10 Client Control TAO allows client to pass large objects by value Pass-By-Reference –Performance not affected by object size Pass-by-value –Performance decreases as size of object increases

11 Client Control

12 Language Transparency TAO does not allow for language transparency for pass-by-value Client must have implementation at compile time Only C++ mapping currently exists

13 Location Transparency Because of separation of ValueBase objects from CORBA objects, client can tell if object is passed by value Interface is written differently for the two types TAO does not define abstract interfaces Lack of location transparency breaks CORBA’s Object Model

14 Performance Pass-by-value improves performance most when –Object is small –Object is referenced multiple times by client –Consistency is not maintained

15 Performance

16 Our Model Consistency –Use classical pass-by-value model (no shared state between client and server) –Only allow pass-by-value for immutable objects Orthogonality –All objects should be CORBA objects –Add byvalue boolean to CORBA objects –Default value of byvalue is false

17 Our Model Client Control –Server decides whether object can be passed by value restricted according to size, immutability, etc. –Client may block pass-by-value send_object() - lets server choose how object is sent send_by_reference() - blocks pass-by-value –Give server more control than client

18 Our Model Language Transparency –No easy solution b/c of range of operating systems, language capabilities –If object’s implementation language is not available on client, default to pass-by-reference –If object’s implementation is not on client, download during first call Assume performance gain makes up for download time

19 Our Model Location Transparency –All objects are CORBA objects assures location transparency for client Performance –Performance gains for small, remote, immutable objects –Performance is one of the key reasons for pass- by-value, and was an important factor in our model design.

20 Conclusion Pass-by-value can improve performance Restricted objects (immutable, small) Good for systems with low bandwidth Simple to allow pass-by-value in older CORBA programs because our model maintains object abstraction Improvement in many ways over CORBA’s OBV and TAO’s pass-by-value service