A Time-Aware Type System For Data-Race Protection and Guaranteed Initialization

We introduce a type system based on intervals, objects representing the time in which a block of code will execute. The type system can verify time-based properties such as when a field will be accessed or a method will be invoked. One concrete application of our type system is data-race protection: For fields which are initialized during one phase of the program and constant thereafter, users can designate the interval during which the field is mutable. Code which happens after this initialization interval can safely read the field in parallel. We also support fields guarded by a lock and even the use of dynamic race detectors. Another use for intervals is to designate different phases in the object’s lifetime, such as a constructor phase. The type system then ensures that only appropriate methods are invoked in each phase

Handling Errors in Parallel Programs Based on Happens Before Relations

Abstract—Intervals are a new model for parallel programming based on an explicit happens before relation. Intervals permit fine-grained but high-level control of the program scheduler, and they dynamically detect and prevent deadlocking schedules. In this paper, we discuss the design decisions that led to the intervals model, focusing on error detection and handling. Our error propagation scheme makes use of the happens before relation to detect and abort dependent tasks that occur between the point where a failure occurs and where the failure is handled. Keywords-exceptions; parallelism; intervals I

Back to the future in one week - implementing a Smalltalk VM in PyPy

We report on our experiences with the Spy project, including implementation details and benchmark results. Spy is a re-implementation of the Squeak (i.e., Smalltalk-80) VM using the PyPy toolchain. The PyPy project allows code written in RPython, a subset of Python, to be translated to a multitude of different backends and architectures. During the translation, many aspects of the implementation can be independently tuned, such as the garbage collection algorithm or threading implementation. In this way, a whole host of interpreters can be derived from one abstract interpreter definition. Spy aims to bring these benefits to Squeak, allowing for greater portability and, eventually, improved performance. The current Spy codebase is able to run a small set of benchmarks that demonstrate performance superior to many similar Smalltalk VMs, but which still run slower than in Squeak itself. Spy was built from scratch over the course of a week during a joint Squeak-PyPy Sprint in Bern last autumn