Section: New Results

Dynamic Languages: Language Constructs for Modular Design

Dynamic Software Update from Development to Production. Dynamic Software Update (DSU) solutions update applications while they are executing. These solutions are typically used in production to minimize application downtime, or in integrated development environments to provide live programming support. Each of these scenarios presents different challenges, forcing existing solutions to be designed with only one of these use cases in mind. For example, DSUs for live programming typically do not implement safe point detection or instance migration, while production DSUs require manual generation of patches and lack IDE integration. Also, these solutions have limited ability to update themselves or the language core libraries, and some of them present execution penalties outside the update window. We propose a DSU (gDSU) that works for both live programming and production environments. Our solution implements safe update point detection using call stack manipulation and a reusable instance migration mechanism to minimize manual intervention in patch generation. Moreover, it also offers updates of core language libraries and the update mechanism itself. This is achieved by the incremental copy of the modified objects and an atomic commit operation. We show that our solution does not affect the global performance of the application and it presents only a run-time penalty during the update window. Our solution is able to apply an update impacting 100,000 instances in 1 second. In this 1 second, only during 250 milliseconds the application is not responsive. The rest of the time the application runs normally while gDSU is looking for the safe update point. The update only requires to copy the elements that are modified. [6]

Implementing Modular Class-based Reuse Mechanisms on Top of a Single Inheritance VM. Code reuse is a good strategy to avoid code duplication and speed up software development. Existing object-oriented programming languages propose different ways of combining existing and new code such as e.g., single inheritance, multiple inheritance, Traits or Mixins. All these mechanisms present advantages and disadvantages and there are situations that require the use of one over the other. To avoid the complexity of implementing a virtual machine (VM), many of these mechanisms are often implemented on top of an existing high-performance VM, originally meant to run a single inheritance object-oriented language. These implementations require thus a mapping between the programming model they propose and the execution model provided by the VM. Moreover, reuse mechanisms are not usually composable, nor it is easy to implement new ones for a given language. We propose a modular meta-level runtime architecture to implement and combine different code reuse mechanisms. This architecture supports dynamic combination of several mechanisms without affecting runtime performance in a single inheritance object-oriented VM. It includes moreover a reflective Meta-Object Protocol to query and modify classes using the programming logical model instead of the underlying low-level runtime model. Thanks to this architecture, we implemented Stateful Traits, Mixins, CLOS multiple inheritance, CLOS Standard Method Combinations and Beta prefixing in a modular and composable way. [15]