Dynamic Query-Based Debugging

Raimondas Lencevicius, Urs Hölzle, and Ambuj K. Singh

Abstract: Program errors are hard to find because of the cause-effect gap between the time when an error occurs and the time when the error becomes apparent to the programmer. Although debugging techniques such as conditional and data breakpoints help to find error causes in simple cases, they fail to effectively bridge the cause-effect gap in many situations. Dynamic query-based debuggers offer programmers an effective tool that provides instant error alert by continuously checking inter-object relationships while the debugged program is running. To speed up dynamic query evaluation, our debugger (implemented in portable Java) uses a combination of program instrumentation, load-time code generation, query optimization, and incremental reevaluation. Experiments and a query cost model show that selection queries are efficient in most cases, while more costly join queries are practical when query evaluations are infrequent or query domains are small.

Keywords: Debugging, Breakpoints, Java, Queries, Class Loaders, Instrumentation

Technical Report TRCS98-34, Computer Science Department, University of California, Santa Barbara, December 1998. Published in the Proceedings of the 13th European Conference on Object-Oriented Programming'99, (ECOOP'99), Lisbon, Portugal, June 1999.

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