7 research outputs found
Programming Not Only by Example
In recent years, there has been tremendous progress in automated synthesis
techniques that are able to automatically generate code based on some intent
expressed by the programmer. A major challenge for the adoption of synthesis
remains in having the programmer communicate their intent. When the expressed
intent is coarse-grained (for example, restriction on the expected type of an
expression), the synthesizer often produces a long list of results for the
programmer to choose from, shifting the heavy-lifting to the user. An
alternative approach, successfully used in end-user synthesis is programming by
example (PBE), where the user leverages examples to interactively and
iteratively refine the intent. However, using only examples is not expressive
enough for programmers, who can observe the generated program and refine the
intent by directly relating to parts of the generated program.
We present a novel approach to interacting with a synthesizer using a
granular interaction model. Our approach employs a rich interaction model where
(i) the synthesizer decorates a candidate program with debug information that
assists in understanding the program and identifying good or bad parts, and
(ii) the user is allowed to provide feedback not only on the expected output of
a program, but also on the underlying program itself. That is, when the user
identifies a program as (partially) correct or incorrect, they can also
explicitly indicate the good or bad parts, to allow the synthesizer to accept
or discard parts of the program instead of discarding the program as a whole.
We show the value of our approach in a controlled user study. Our study shows
that participants have strong preference to using granular feedback instead of
examples, and are able to provide granular feedback much faster
Formal Derivation of Concurrent Garbage Collectors
Concurrent garbage collectors are notoriously difficult to implement
correctly. Previous approaches to the issue of producing correct collectors
have mainly been based on posit-and-prove verification or on the application of
domain-specific templates and transformations. We show how to derive the upper
reaches of a family of concurrent garbage collectors by refinement from a
formal specification, emphasizing the application of domain-independent design
theories and transformations. A key contribution is an extension to the
classical lattice-theoretic fixpoint theorems to account for the dynamics of
concurrent mutation and collection.Comment: 38 pages, 21 figures. The short version of this paper appeared in the
Proceedings of MPC 201
Correctness-preserving derivation of concurrent garbage collection algorithms
Constructing correct concurrent garbage collection algorithms is notoriously hard. Numerous such algorithms have been proposed, implemented, and deployed – and yet the relationship among them in terms of speed and precision is poorly understood, and the validation of one algorithm does not carry over to others. As programs with low latency requirements written in garbagecollected languages become part of society’s mission-critical infrastructure, it is imperative that we raise the level of confidence in the correctness of the underlying system, and that we understand the trade-offs inherent in our algorithmic choice. In this paper we present correctness-preserving transformations that can be applied to an initial abstract concurrent garbage collection algorithm which is simpler, more precise, and easier to prove correct than algorithms used in practice — but also more expensive and with less concurrency. We then show how both pre-existing and new algorithms can be synthesized from the abstract algorithm by a series of our transformations. We relate the algorithms formally using a new definition of precision, and informally with respect to overhead and concurrency. This provides many insights about the nature of concurrent collection, allows the direct synthesis of new and useful algorithms, reduces the burden of proof to a single simple algorithm, and lays the groundwork for the automated synthesis of correct concurrent collectors
Correctness-preserving derivation of concurrent garbage collection algorithms
Constructing correct concurrent garbage collection algorithms is notoriously hard. Numerous such algorithms have been proposed, implemented, and deployed – and yet the relationship among them in terms of speed and precision is poorly understood, and the validation of one algorithm does not carry over to others. As programs with low latency requirements written in garbagecollected languages become part of society’s mission-critical infrastructure, it is imperative that we raise the level of confidence in the correctness of the underlying system, and that we understand the trade-offs inherent in our algorithmic choice. In this paper we present correctness-preserving transformations that can be applied to an initial abstract concurrent garbage collection algorithm which is simpler, more precise, and easier to prove correct than algorithms used in practice — but also more expensive and with less concurrency. We then show how both pre-existing and new algorithms can be synthesized from the abstract algorithm by a series of our transformations. We relate the algorithms formally using a new definition of precision, and informally with respect to overhead and concurrency. This provides many insights about the nature of concurrent collection, allows the direct synthesis of new and useful algorithms, reduces the burden of proof to a single simple algorithm, and lays the groundwork for the automated synthesis of correct concurrent collectors