The Alta Operating System

Many modern systems, including web servers, database engines, and operating system kernels, are using language-based protection mechanisms to provide the safety and integrity traditionally supplied by hardware. As these language-based systems become used in more demanding situations, they are faced with the same problems that traditional operating systems have solved—namely shared resource management, process separation, and per-process resource accounting. While many incremental changes to language-based, extensible systems have been proposed, this thesis demonstrates that comprehensive solutions used in traditional operating systems are applicable and appropriate. This thesis describes Alta, an implementation of the Fluke operating system’s nested process model in a Java virtual machine. The nested process model is a hierarchical operating system process model designed to provide a consistent approach to user-level, per-process resource accounting and control. This model accounts for CPU usage, memory, and other resources through a combination of system primitives and a flexible, capability-based mechanism. Alta supports nested processes and interprocess communication. Java applications running on Alta can create child processes and regulate the resources—the environment—of those processes. Alta demonstrates that the Java environment is sufficient for hosting traditional operating system abstractions. Alta extends the nested process model to encompass Java-specific resources such as class files, modifies the model to leverage Java’s type safety, and extends the Java type system to support safe fine-grained sharing between different applications. Existing Java applications work without modification on Alta. Alta is compared in terms of structure, implementation and performance to Fluke and traditional hardware-based operating systems. A small set of test applications demonstrate flexible, application-level control over memory usage and file access.