Pass-By-Value Services
in
Object Component Software
Group 1
Yannick Loitiere
Andrea Rowan
Michele Co
Jinze Liu
1
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
2
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
3
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
4
Related Work
• Ennio Grasso’s Model
– Consistency maintained
– All objects CORBA objects
• CORBA 2.3 OBV Model
– No consistency
– Separate ValueBase objects
5
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
6
Evaluation of Models
•
•
•
•
•
•
Consistency
Orthogonality / Semantics
Client Control
Language Transparency
Location Transparency
Performance
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Consistency
Time to Retrieve and
Modify One Long (s)
Performance for Pass-By-Value Models
With and Without Client/Server Consistency
0.005
0.004
Inconsistent Pass-ByValue
0.003
Consistent Pass-ByValue
0.002
0.001
0
1
21
51
201
501
Number of Longs Stored in Object
8
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
9
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
10
Client Control
Time to Retrieve and
Modify One Long (s)
Performance for Calling Objects of Different Sizes
0.003
0.0025
0.002
Pass-By-Value
0.0015
Pass-By-Reference
0.001
0.0005
0
1
21
51
201
501
Number of Longs Stored in Object
11
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
12
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
13
Performance
• Pass-by-value improves performance most
when
– Object is small
– Object is referenced multiple times by client
– Consistency is not maintained
14
Performance
Performance Time (s)
Performance For Multiple Accesses of Small Object
0.012
0.01
Inconsistent Pass-ByValue
0.008
0.006
Consistent Pass-ByValue
0.004
Pass-By-Reference
0.002
0
1
10
Number of Accesses
15
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
16
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
17
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
18
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 passby-value, and was an important factor in our
model design.
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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
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