ITR: Adaptive Protocols for a Distributed Java Virtual Machine

Java 是一种越来越重要的语言，但迄今为止，Java 中的并行性仅限于对称多处理器 (SMP) 上的多线程或使用远程方法调用 (RMI) 的分布式计算。 基于Java的互联网相关应用程序的数量和规模要求越来越多的并行性和系统可扩展性。 该提案解决了为分布式 Java 虚拟机设计内存一致性协议的问题，该虚拟机能够在运行时自适应不同的应用程序特征。拟议的工作分为五个任务：（1）内存一致性模型的定义，（2）一致性协议的开发，（3）自适应协议所基于的分析性能模型的定义，（4）负载平衡的处理器分配算法的开发，以及（5）使用四类应用程序评估系统性能。必须首先定义正确的分布式Java虚拟机规范。由于Sun规范和分布式内存架构之间的不兼容，正确性问题对于分布式共享内存Java虚拟机尤为重要。初步工作表明Sun 的JVM 规范对于DSM 架构而言过于强大。对 JVMS 需求的彻底分析将产生一组约束，必须从原始 Sun 的 JVMS 中放宽这些约束，才能实现高效的分布式实现。一旦建立了理论上的内存一致性模型，下一步就是开发一致性协议。提出了一种分析模型来分析各种协议的应用行为。应用程序配置文件可以通过对象粒度、访问的时间局部性和对象访问模式来抽象。所提出的工作的新颖之处在于使用分析模型参数将应用程序参数映射到协议参数：线程创建时间、同步时间和执行开销。这些参数可以通过分析进行估计和测量。 需要研究模型参数和自适应协议之间的相关性。有必要开发将参数与协议联系起来的启发式方法。作为前期工作的一部分，名为 DISK 的分布式 Java 虚拟机已在我们的工作站网络实验室中实现，该实验室由 16 台通过 100 Mbps 网络连接的 Pentium III 计算机组成。 DISK 目前支持两种内存一致性协议：无效和更新延迟释放一致性协议。将研究几个特定于 Java 的应用程序，以测量和调整所开发的自适应协议的性能。来自互联网和知识处理技术的四种不同类别的应用程序将被用作新的基准：（1）客户端I/O密集型应用程序，（2）服务器端I/O密集型应用程序，（3）计算密集型应用程序，以及（4）计算和I/O密集型应用程序。

Java is a language of growing importance but so far parallelism in Java has been limited to either multi-threading on symmetric multiprocessors (SMP) or distributed computing using Remote MethodInvocation (RMI). The number and size of Java-based Internet-related applications require more and more parallelism and system scalability. This proposal addresses the problem of designing memory consistencyprotocols for a distributed Java Virtual Machine capable of self-adapting at runtime to different application characteristics. The proposed work is divided into five tasks: (1) the definition of the memory consistency model, (2) the development of consistency protocols, (3) the definition of an analytical performance model on whichadaptive protocols are based, (4) the development of processor allocation algorithms for load balancing, and (5) the evaluation of the system performance using four classes of applications.A correct distributed Java Virtual Machine specification must be first defined. The correctness issue is especially important for a distributed shared memory Java Virtual Machine due to the incompatibilities between the Sun specification and distributed memory architectures. Preliminary work indicates that Sun's JVM specification is too strong for DSM architectures. A thorough analysis of the JVMS requirements will produce the set of constraints that have to be relaxed from the original Sun's JVMS to allow an efficient distributed implementation. Once a theoretical memory consistency model is established, the next step is to develop consistency protocols. An analytical model is proposed to analyze the application behavior for various protocols. The application profile can be abstracted by the object granularity, temporal locality of accesses, and object accesspatterns. A novelty of the proposed work is the mapping of application parameters into protocol parameters using the analytical model parameters: thread creation time, synchronization time, and executionoverhead. These parameters can be estimated analytically and measured. The correlation between model parameters and adaptive protocols needs to be investigated. It is necessary to develop heuristics that linkparameters with the protocols. As part of the preliminary work, a distributed Java Virtual Machine called DISK has been implemented in our network-of-workstations laboratory consisting of sixteen Pentium III computers connected by a100 Mbps network. DISK currently supports two memory consistency protocols: an invalidate and an update lazy release consistency protocol. Several Java-specific applications will be investigated to measure and tune the performance of the adaptive protocols developed. Four different classes of applications from the Internet and knowledge processing technology will be used as new benchmarks: (1) client-side I/O intensive applications, (2) server-side I/O intensive applications, (3) computational intensive applications, and(4) computational and I/O intensive applications.