On Exceptions, Events and Observer Chains

By: Mehdi Bagherzadeh, Hridesh Rajan, and Ali Darvish

Abstract

Modular understanding of behaviors and flows of exceptions may help in their better use and handling. Such reasoning tasks about exceptions face unique challenges in event-based implicit invocation (II) languages that allow subjects to implicitly invoke observers, and run the observers in a chain. In this work, we illustrate these challenge in Ptolemy and propose Ptolemy-X that enables modular reasoning about behaviors and flows of exceptions for event announcement and handling. Ptolemy-X’s exception-aware specification expressions and boundary exceptions limit the set of (un)checked exceptions of subjects and observers of an event. Exceptional postconditions specify the behaviors of these exceptions. Greybox specifications specify the flows of these exceptions among the observers in the chain. Ptolemy-X’s type system and refinement rules enforce these specifications and thus enable its modular reasoning. We evaluate the utility of Ptolemy-X’s exception flow reasoning by applying it to understand a set of aspect-oriented (AO) bug patterns. We also present Ptolemy-X’s semantics including its sound static semantics.

ACM Reference

Bagherzadeh, M. et al. 2013. On Exceptions, Events and Observer Chains. AOSD ’13: 12th International Conference on Aspect-Oriented Software Development (Mar. 2013).

BibTeX Reference

@inproceedings{bagherzadeh2013exceptions,
  author = {Mehdi Bagherzadeh and Hridesh Rajan and Ali Darvish},
  title = {On Exceptions, Events and Observer Chains},
  booktitle = {AOSD '13: 12th International Conference on Aspect-Oriented Software Development},
  location = {Fukuoka, Japan},
  month = {March},
  year = {2013},
  entrysubtype = {conference},
  abstract = {
    Modular understanding of behaviors and flows of exceptions may help in their
    better use and handling. Such reasoning tasks about exceptions face unique
    challenges in event-based implicit invocation (II) languages that allow
    subjects to implicitly invoke observers, and run the observers in a chain. In
    this work, we illustrate these challenge in Ptolemy and propose Ptolemy-X that
    enables modular reasoning about behaviors and flows of exceptions for event
    announcement and handling. Ptolemy-X's exception-aware specification
    expressions and boundary exceptions limit the set of (un)checked exceptions of
    subjects and observers of an event. Exceptional postconditions specify the
    behaviors of these exceptions. Greybox specifications specify the flows of
    these exceptions among the observers in the chain. Ptolemy-X's type system and
    refinement rules enforce these specifications and thus enable its modular
    reasoning. We evaluate the utility of Ptolemy-X's exception flow reasoning by
    applying it to understand a set of aspect-oriented (AO) bug patterns. We also
    present Ptolemy-X's semantics including its sound static semantics.
  }
}