A Unified Framework for Verification Techniques for Object Invariants

Abstract

Abstract. Object invariants define the consistency of objects. They have subtle semantics, mainly because of call-backs, multi-object invariants, and subclassing. Several verification techniques for object invariants have been proposed. It is difficult to compare these techniques, and to ascertain their soundness, because of their differences in restrictions on programs and invariants, in the use of advanced type systems (e.g., ownership types), in the meaning of invariants, and in proof obligations. We develop a unified framework for such techniques. We distil seven parameters that characterise a verification technique, and identify sufficient conditions on these parameters which guarantee soundness. We instantiate our framework with three verification techniques from the literature, and use it to assess soundness and compare expressiveness.

A Discipline for Program Verification Based on Backpointers and Its Use in Observational Disjointness

“…Some other conditions are given by the programmer, for example object or monitor invariants. There are several flavors of treating program-specific invariants, mostly focusing on the special case of object invariants [7]. Various forms of ownership [1,13] are popular invariant disciplines.…”

Verifying Class Invariants in Concurrent Programs

“…Both concepts, as well as Lu et al's modular technique [16], are designed for ownership-based type systems. These techniques are captured in Drossopoulou et al's abstract unified framework [9]. Although it is stated that this abstract framework should be suitable to model class invariants in a concurrent setting, the framework has never been applied on a concrete verification technique for concurrent programs.…”

Dynamic Boundaries: Information Hiding by Second Order Framing with First Order Assertions

“…Moreover, code within the module, acting on one instance of Set, could violate the invariant of another instance. Besides scope and typing, a popular technique to deal with encapsulation in the presence of pointers is "ownership" (e.g., [9,11]). Ownership systems ghost freed : rgn; var flist : Node; count : int;…”

“…Drossopoulou et al [11] introduce a general framework to describe verification techniques for invariants. A number of ownership disciplines from the literature are studied as instances of the framework.…”

“…Reynolds gave a derivation using the rule of conjunction 10 that shows the SOF rule of SL is not sound without restriction to predicates that are "precise" in the sense of determining a unique footprint [31]. 11 The semantic analysis in [31] shows that the need for a unique footprint applies to region logic as well. However, region logic separates the footprint from the formula, allowing the invariant formula to denote an imprecise predicate while framing the formula by effects that in a given state determines a unique set of locations.…”