Gregory H. Cooper

Flapjax: a programming language for Ajax applications

This paper presents Flapjax, a language designed for contemporary Web applications. These applications communicate with servers and have rich, interactive interfaces. Flapjax provides two key features that simplify writing these applications. First, it provides event streams, a uniform abstraction for communication within a program as well as with external Web services. Second, the language itself is reactive: it automatically tracks data dependencies and propagates updates along those dataflows. This allows developers to write reactive interfaces in a declarative and compositional style. Flapjax is built on top of JavaScript. It runs on unmodified browsers and readily interoperates with existing JavaScript code. It is usable as either a programming language (that is compiled to JavaScript) or as a JavaScript library, and is designed for both uses. This paper presents the language, its design decisions, and illustrative examples drawn from several working Flapjax applications.

Embedding dynamic dataflow in a call-by-value language

This paper describes FrTime, an extension of Scheme designed for writing interactive applications. Inspired by functional reactive programming, the language embeds dynamic dataflow within a call-by-value functional language. The essence of the embedding is to make program expressions evaluate to nodes in a dataflow graph. This strategy eases importation of legacy code and permits incremental program construction. We have integrated FrTime with the DrScheme programming environment and have used it to develop several novel applications. We describe FrTimes design and implementation in detail and present a formal semantics of its evaluation model.

Real-time CORBA

This paper presents a survey of results in developing Real-Time CORBA, a standard for real-time management of distributed objects. This paper includes background on two areas that have been combined to realize Real-Time CORBA: the CORBA standards that have been produced by the international Object Management Group; and techniques for distributed real-time computing that have been produced in the research community. The survey describes major RT CORBA research efforts, commercial development efforts, and standardization efforts by the Object Management Group.

Thialfi: a client notification service for internet-scale applications

Ensuring the freshness of client data is a fundamental problem for applications that rely on cloud infrastructure to store data and mediate sharing. Thialfi is a notification service developed at Google to simplify this task. Thialfi supports applications written in multiple programming languages and running on multiple platforms, e.g., browsers, phones, and desktops. Applications register their interest in a set of shared objects and receive notifications when those objects change. Thialfi servers run in multiple Google data centers for availability and replicate their state asynchronously. Thialfis approach to recovery emphasizes simplicity: all server state is soft, and clients drive recovery and assist in replication. A principal goal of our design is to provide a straightforward API and good semantics despite a variety of failures, including server crashes, communication failures, storage unavailability, and data center failures. Evaluation of live deployments confirms that Thialfi is scalable, efficient, and robust. In production use, Thialfi has scaled to millions of users and delivers notifications with an average delay of less than one second.

Lowering: a static optimization technique for transparent functional reactivity

Functional Reactive Programming (FRP) extends traditional functional programming with dataflow evaluation, making it possible to write interactive programs in a declarative style. An FRP language creates a dynamic graph of data dependencies and reacts to changes by propagating updates through the graph. In a transparent FRP language, the primitive operators are implicitly lifted, so they construct graph nodes when they are applied to time-varying values. This model has some attractive properties, but it tends to produce a large graph that is costly to maintain. In this paper, we develop a transformation we call lowering, which improves performance by reducing the size of the graph. We present a static analysis that guides the sound application of this optimization, and we present benchmark results that demonstrate dramatic improvements in both speed and memory usage for real programs.

Crossing state lines: adapting object-oriented frameworks to functional reactive languages

Functional reactive programming integrates dynamic dataflow with functional programming to offer an elegant and powerful model for expressing computations over time-varying values. Developing realistic applications, however, requires access to libraries, such as those for GUIs, that are written in mainstream object-oriented languages. Previous work has developed functional reactive interfaces for GUI toolkits but has not provided an account of the principles underlying the implementation strategy. In this paper, we investigate this problem by studying the adaptation of the object-oriented toolkit MrEd to the functional reactive language FrTime. The heart of this problem is how to communicate state changes between the application and the toolkits widget objects. After presenting a basic strategy for adaptation, we discuss abstraction techniques based on mixins and macros that allow us to adapt numerous properties in many widget classes with minimal code duplication. This results in a wrapper for the entire MrEd toolkit in only a few hundred lines of code. We also briefly discuss a spreadsheet developed with the resulting toolkit.

The design and implementation of a dataflow language for scriptable debugging

Debugging is a laborious, manual activity that often involves the repetition of common operations. Ideally, users should be able to describe these repetitious operations as little programs. Debuggers should therefore be programmable, or scriptable. The operating environment of these scripts, however, imposes interesting design challenges on the programming language in which these scripts are written.This paper presents our design of a language for scripting debuggers. The language offers powerful primitives that can precisely and concisely capture many important debugging and comprehension metaphors. The paper also describes a pair of debuggers, one for Java and the other for Scheme, built in accordance with these principles. The paper includes concrete examples of applying this debugger to programs.

Concurrency control in real-time object-oriented systems: the affected set priority ceiling protocols

This paper presents the affected set priority ceiling protocols (ASPCP) for concurrency control in real-time object-oriented systems. These protocols are based on a combination of semantic locking and priority ceiling techniques. This paper shows that the ASPCP protocols provide higher potential concurrency for object-oriented systems than existing priority ceiling protocols, while still bounding priority inversion and preventing deadlock.

A dataflow language for scriptable debugging

Debugging is a laborious, manual activity that often involves the repetition of common operations. Ideally, users should be able to describe these repetitious operations as little programs. Debuggers should therefore be programmable, or scriptable. The operating environment of these scripts, however, imposes interesting design challenges on the programming language in which these scripts are written. This paper presents our design of a language for scripting debuggers. The language offers powerful primitives that can precisely and concisely capture many important debugging and comprehension metaphors. The paper also describes a debugger for the Java language built in accordance with these principles. We have implemented this debugger to run alongside the Java virtual machine. The paper includes concrete examples of applying this debugger to programs

Teaching garbage collection without implementing compiler or interpreters

Given the widespread use of memory-safe languages, students must understand garbage collection well. Following a constructivist philosophy, an effective approach would be to have them implement garbage collectors. Unfortunately, a full implementation depends on substantial knowledge of compilers and runtime systems, which many courses do not cover or cannot assume. This paper presents an instructive approach to teaching GC, where students implement it atop a simplified stack and heap. Our approach eliminates enormous curricular dependencies while preserving the essence of GC algorithms. We take pains to enable testability, comprehensibility, and facilitates debugging. Our approach has been successfully classroom-tested for several years at several institutions.