Optimization of Exception Handling

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Optimization of Exception Handling

• Kris Hjelmeland

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Introduction

• Why is exception handling important?

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What is Exception Handling?

• An exception is a computational state that
  requires an extraordinary computation.
• A handler is a code fragment that deals with an
  exception occurrence.

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Strategies for Handling Exceptions

• Take Control so program can continue
• Throw for handling elsewhere
• Ignore the problem altogether

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Exception Handling in Languages

• Languages like C, return a value from a function
  call.
• Java and C use exception handling mechanisms.

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Java Exception Handling in the JVM

• Exception is thrown
  
• JVM searches table for handler
• System branches to handler
• If handler not found
• Search continues up hierarchy
• Thread will terminate if an appropriate handler
  does not exist

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Exception Handling Techniques

• Return Code
• if(returnvalue errorvalue)
• //do error handling
• Status Flag

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Drawbacks of Older Techniques

• Dependent on programmer
• Requires timely error checking
• Reduces readability
• Error checking omissions

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Goals of an Exception Handling Mechanism

• Alleviate testing throughout the program
• Prevent incomplete operations from continuing
• Allow for the adding, changing, and removing of
  exceptions

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Optimization of EHM

• Suggested EHM Requirements
• Appropriate Handling Models
• Integration of Optimal Features

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Suggested EHM Requirements

• Reusability
• Encapsulation
• Totality
• Consistency
• Readability

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Reusability

• Object-oriented design provides reusability
• Most software components are reusable
• Reusability saves time and resources.

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Encapsulation

• Encloses data, methods, and definitions in a
  class capsule
• Separates the interface from the definition
• Helps provide better readability and reusability

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Totality

• Must detect all different types of errors
• Must protect against all state and timing errors
• Solutions need to encompass the entire program.

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Consistency

• Program should return to its original state after
  an error
• All resources should be cleaned up after an
  exception terminates
• Shared data and resources must be maintained

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Readability

• Exception handling should not cause errors
  because of messy code
• Separating the exception handling code from main
  execution code is optimal.

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Inadequate Readability

• int error_value -1
• if(functionCall1() error_value)
• //fix the error
• if(functionCall2() error_value)
• //fix the error
• if(functionCall3() error_value)
• //fix the error

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Adequate Readability

• try
• functioncall1()
• functioncall2()
• functioncall3()
• catch(Exception e)
• //fix the error

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Handling Models

• Termination Model
• An alternative operation to its guarded block
• Resumption Model
• Very similar to a routine or method call

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Optimal Features

• Catch-any and Reraise
• Pass exception to an appropriate place
• Derived Exceptions
• Allows for a hierarchy of exceptions
• Exception Parameters
• Pass data along to the handler

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Conclusion

• The optimization of exception handling
  affectively returns life to normal.

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References

• Borger, E. and Schulte, W. "A Practical Method of
  Specification and Analysis of Exception Handling
  - A Java/JVM Case Study," IEEE Transactions on
  Software Engineering, vol. 25, no. 9, September
  2000.
• Buhr, B. A. and Russell Mok, W. Y., "Advanced
  Exception Handling Mechanisms," IEEE Transactions
  On Software Engineering, vol. 26, no. 9,
  September 2000.
• Knudsen, J., L. "Exception Handling Versus Fault
  Tolerance," Exception Handling in Object Oriented
  Systems Workshop at ECOOP'2000, June 12, 2000.
• Lang, J. and David, S. B., "A study of the
  applicability of existing exception handling
  techniques to component-based real-time software
  technology," ACM Transactions on Programming
  Languages Systems, vol. 20, no. 2, p. 274,
  March 1998.
• Maxion, R. A. and Olszewski, R. T., "Eliminating
  Exception Handling Errors with Dependability
  Cases A Comparative, Empirical Study," IEEE
  Transactions on Software Engineering, vol. 25,
  no. 9, September 2000.
• Mikhailova, A. and Romanovsky A.,
  "Behavior-Preserving Evolution of Interface
  Exceptions,Exception Handling in Object Oriented
  Systems Workshop at ECOOP'2000, June 12, 2000.
• Waldo, J. "Throwing Things," UNIX Review's
  Performance Computing, vol. 16, p71, May 1998.

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Optimization of Exception Handling

• Thank You
• Kris Hjelmeland