Practical API Protocol Checking with Access Permissions

Abstract

Abstract. Reusable APIs often de ne usage protocols. We previously developed a sound modular type system that checks compliance with typestate-based protocols while a ording a great deal of aliasing exibility. We also developed Plural, a prototype tool that embodies our approach as an automated static analysis and includes several extensions we found useful in practice. This paper evaluates our approach along the following dimensions: (1) We report on experience in specifying relevant usage rules for a large Java standard API with our approach. We also specify several other Java APIs and identify recurring patterns. (2) We summarize two case studies in verifying third-party open-source code bases with few false positives using our tool. We discuss how tool shortcomings can be addressed either with code refactorings or extensions to the tool itself. These results indicate that our approach can be used to specify and enforce real API protocols in practice.

Checking Concurrent Typestate with Access Permissions in Plural: A Retrospective

“…Plural is envisioned to work like a typechecker and hence sound [6,3] so false negatives cannot occur. Empirically we found Plural's false positive rate to be less than 6 false positives per kloc in sample open-source programs [7].…”

“…Modular checking means we would like to check code one method at a time, using only the specifications of other objects; this requires us to describe the protocol and aliasing state of objects at method boundaries. We accomplish both tasks using access permissions [6], which we have implemented in Plural [7], an automated tool for checking permission-based typestate protocols in Java. This section is a review of previously published work [6,3,7].…”

“…Our tool, Plural 2 , is a plug-in to the Eclipse IDE that implements a previously developed type system [6,3] as a static dataflow analysis for Java [7]. In the remainder of this section we show example annotations and explain how permissions are tracked and API implementations are verified.…”

Searching the State Space: A Qualitative Study of API Protocol Usability

“…Neither Beckman nor Whaley identified any protocols in interfaces, so 9 interfaces were added from other sources (e.g. Bierhoff et al [4]). These interfaces are not implemented in the Java Standard Library, but they are implemented by many third parties, and so the interface protocols can be very widely used.…”

“…Many tools verify protocols (e.g. Bierhoff et al [4], Dwyer et al [9], Foster et al [11]). These tools require programmers to specify protocols using alias and typestate annotations separate from code.…”