Weakly Consistent Memories

共享内存是并行系统中一个非常重要的抽象概念。提供跨分布式硬件的共享内存抽象可能同样重要，因为它允许进程统一访问本地和远程信息。然而，在分布式环境中实现一致的共享内存不仅成本高昂，而且还存在延迟和可伸缩性等基本问题。最近的研究结果表明，原则上削弱内存一致性可以减少一致性维护的成本，同时保持一个可行的编程模型。本项目将探讨弱一致性记忆研究中出现的理论和实践问题。理论工作将包括对现有和新记忆的正式描述，以及对当记忆一致性减弱时正确执行的程序属性的调查。这项研究的结果将增强我们对弱记忆的基本理解。为了证明弱记忆可以很容易地编程并导致性能的提高，实际工作将研究弱一致性记忆的编程和实现。使用弱一致性内存的程序员可以“直接”为每周一致性模型编写程序，或者为传统的一致性内存编写的程序可以转换为在弱一致性内存上更有效地运行。该项目将确定适合弱内存的应用领域，开发简化这些内存编程的习惯用法，并开发弱一致性内存的高效分布式实现。由于应用程序可以在一致内存和弱内存上进行不同的编程，因此总体性能取决于应用程序的算法效率和底层弱内存实现的性能。因此，这项工作包括实验研究，使用执行加速和消息开销等度量来研究原型系统的整体性能。对弱一致性存储器的理论和实践进行全面的研究将产生适用于分布式系统和大规模多处理器的实质性好处。

Shared memory is a fundamentally important abstraction in parallel systems. Providing a shared memory abstraction across distributed hardware may prove equally important because it allows processes to access local and remote information uniformly. However, implementing consistent shared memory in a distributed environment is not only costly but also has fundamental problems of latency and scale. The results of recent research suggest that the principled weakening of memory consistency can reduce the cost of consistency maintenance while maintaining a viable model for programming. This project will investigate both theoretical and practical issues arising from the study of weakly consistent memories. The theoretical work will include a formal characterization of both existing and new memories and an investigation of properties of programs that execute correctly when memory consistency is weakened. The results of this research will enhance our fundamental understanding of weak memories. To demonstrate that weak memories can be easily programmed and lead to improved performance, the practical work will investigate programming and implementation of weakly consistent memories. Programmers of weakly consistent memories may write programs "directly" for the weekly consistent model, or programs written for traditional consistent memory may be transformed to run more efficiently on a weakly consistent memory. The project will identify application domains suitable for weak memories, develop idioms that simplify the programming of these memories, and develop efficient distributed implementations of weakly consistent memories. Since an application may be programmed differently on consistent and weak memories, overall performance depends both on the algorithmic efficiency of the application and the performance of the underlying weak memory implementation. Therefore, the work includes experimental research to study the overall performance of a prototype system using measures such as execution speedup and message overhead. Comprehensive investigation of the theory and practice of weakly consistent memories will yield substantial benefits applicable to both distributed systems and large scale multiprocessors.