Section: New Results

Reconciling Dynamic Languages and Isolation

Virtual Smalltalk Images: Model and Applications. Reflective architectures are a powerful solution for code browsing, debugging or in-language process handling. However, these reflective architectures show some limitations in edge cases of self-modification and self-monitoring. Modifying the modifier process or monitoring the monitor process in a reflective system alters the system itself, leading to the impossibility to perform some of those tasks properly. We analyze the problems of reflective architectures in the context of image based object-oriented languages and solve them by providing a first-class representation of an image: a virtualized image. We present Oz, our virtual image solution. In Oz, a virtual image is represented by an object space. Through an object space, an image can manipulate the internal structure and control the execution of other images. An Oz object space allows one to introspect and modify execution information such as processes, contexts, existing classes and objects. We show how Oz solves the edge cases of reflective architectures by adding a third participant, and thus, removing the self modification and self-observation constraints. [30]

Bootstrapping Reflective Systems: The Case of Pharo. Bootstrapping is a technique commonly known by its usage in language definition by the introduction of a compiler written in the same language it compiles. This process is important to understand and modify the definition of a given language using the same language, taking benefit of the abstractions and expression power it provides. A bootstrap, then, supports the evolution of a language. However, the infrastructure of reflective systems like Smalltalk includes, in addition to a compiler, an environment with several self-references. A reflective system bootstrap should consider all its infrastructural components. We propose a definition of bootstrap for object-oriented reflective systems, we describe the architecture and components it should contain and we analyze the challenges it has to overcome. Finally, we present a reference bootstrap process for a reflective system and Hazelnut, its implementation for bootstrapping the Pharo Smalltalk-inspired system. [15]

Object Graph Isolation with Proxies More and more software systems are now made of multiple collaborating third-party components. Enabling fine-grained control over the communication between components becomes a major requirement. While software isolation has been studied for a long time in operating systems (OS), most programming languages lack support for isolation. In this context we explore the notion of proxy. A proxy is a surrogate for another object that controls access to this object. We are particularly interested in generic proxy implementations based on language-level reflection. We present an analysis that shows how these reflective proxies can propagate a security policy thanks to the transitive wrapping mechanism. We present a prototype implementation that supports transitive wrapping and allows a fine-grained control over an isolated object graph. [33]