Construction of Cooperative Distributed Systems

本研究的目的是探讨如何建构具有高度可扩充性与弹性的“合作式”分散式系统。实现协同分布式系统的技术要点有三点：（1）一种虚拟存储器管理机制，其促进进程之间的紧密交互，即使它们驻留在单独的地址空间中，（2）一种通信机制，其使得进程能够协作而不破坏它们各自的功能性和安全性，（3）在进程执行期间改变进程动作（或规范）的机制。第一点是通过在线性64位地址空间上引入一种称为“版本化单级存储”的地址空间管理新概念来实现的。版本化单级存储集成了二级存储和虚拟存储的管理，从而为用户程序提供了计算机系统的整个存储的统一视图。单级存储消除了易失性数据（主存储上的数据）和持久性数据（辅助存储上的数据）之间的操作差异。易失性和持久性数据的统一视图有助于进程协作，这在传统系统上是困难的，因为它们几乎不支持在单独的地址空间之间共享数据和控制。第二点和第三点是通过“触发”机制实现的。触发器系统通知用户操作系统中特定事件的发生，诸如对文件系统中特定文件的读和写、来自/到进程的特定消息的传递、虚拟存储器保护的发生等。通过揭示传统系统对用户程序隐藏的这些事件，用户程序获得了监视系统中的活动的能力，并根据外部环境的变化改变自己的行为。

The purpose of this research was to investigate the method for constructing "cooperative" distributed systems with high extensibility and flexibility. The technical points for realizing cooperative distributed systems are three-fold : (1) a virtual memory management mechanism that facilitates close interaction among processes, even if they reside in separate address spaces, (2) a communication mechanism that enables cooperation of processes without spoiling their individual functionalities and security, (3) a mechanism for changing the action (or specification) of processes during their execution. The first point was achieved by introducing a novel concept for address space management called "versioned single-level store" on a linear 64-bit address spaces. The versioned single-level store integrates the management of secondary storage and virtual memory, thereby providing user programs a uniform view of whole storage of a computer system. The single-level store eliminates the operational differences between the volatile data (those on the primary storage) and persistent data (those on the secondary storage). The uniform view of volatile and persistent data helps processes to cooperate, which has been difficult on conventional systems because they provides little support for sharing data and control among separate address spaces. The second and third point was realized by the "trigger" mechanism. The trigger system notifies users of an occurrence of specific events in the operating system, such as read and write on a specific file in the file system, delivery of a specific message from/to a process, occurrence of virtual memory protection, and so on. By revealing these events that conventional systems have hidden from the user programs, user programs gained the ability of monitoring the activities in the system, and change their own behavior according to the change of the outer environment.