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"Finding and Preventing Run-Time Error Handling Mistakes"
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Finding and Preventing Run-Time Error Handling Mistakes
Meeting Rooms 1-3
Thursday, 11:00, 30 minutes | 7 | · | 8 | · | 9 | · | 10 | · | 11 | · | 12 | · | 13 | · | 14 | · | 15 | · | 16 | · | 17 | · | 18 | · | 19 | · | 20 | · | 21 |
Westley Weimer, UC Berkeley
George Necula, UC Berkeley
It is difficult to write programs that behave correctly in the presence of
run-time errors. Existing programming language features often provide poor
support for executing clean-up code and for restoring invariants in such
exceptional situations. We present a dataflow analysis for finding a
certain class of error-handling mistakes: those that arise from a failure
to release resources or to clean up properly along all paths. Many
real-world programs violate such resource safety policies because of
incorrect error handling. Our flow-sensitive analysis keeps track of
outstanding obligations along program paths and does a precise modeling of
control flow in the presence of exceptions. Using it, we have found over
800 error handling mistakes almost 4 million lines of Java code.
The analysis is unsound and produces false positives, but a few simple
filtering rules suffice to remove them in practice. The remaining mistakes
were manually verified. These mistakes cause sockets, files and database handles to be leaked along some paths. We present a characterization of the most common causes of those errors and discuss the limitations of exception handling,
finalizers and destructors in addressing them. Based on those errors, we propose a programming language feature that keeps track of obligations at run time and ensures that they are discharged. Finally, we present case studies to demonstrate that this feature is natural, efficient, and can improve reliability; for example, retrofitting a 34kLOC program with it resulted in a 0.5% code size decrease, a surprising 17% speed increase (from correctly deallocating resources in the presence of exceptions), and more consistent behavior.
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