Chapter 7
Conclusion

Alta demonstrates the applicability of operating system concepts to a Java virtual machine, leveraging type-safety where a traditional operating system would leverage hardware-based protection mechanisms. Alta is also evidence that standard operating system abstractions can be easily implemented in Java, and that traditional kernel implementation techniques are applicable in a Java-based operating system.

The work presented in this thesis makes the following four additional contributions to language-based operating system research:

• Extensions to the Java type system to support safe sharing between different applications and a facility for renaming classes: Definitions of class and class equality in a system with partially inconsistent typespaces were presented along with a simple algorithm for determining if two classes are safe for sharing between disjoint typespaces.
• Implementation of the Fluke nested process model in Java: Alta demonstrates the applicability of Fluke's nested process model to Java. By duplicating the design, and in many ways the implementation, of Fluke in Alta, I was able to evaluate the influence of Java's programming model on Alta's structure. Additionally, using several detailed performance studies, I identified some of the strengths and weaknesses of Java as a systems programming language.
• Support for multiple applications in a single Java virtual machine: Alta demonstrates that a language-based operating system can, to a large degree, control and separate applications as effectively as a traditional, hardware-based operating system without sacrificing Java's safe, fine-grained sharing.
• Mechanisms for resource control in a Java virtual machine: Direct mechanisms to account for the total memory usage of a Java application were demonstrated for Alta. Capabilities, a standard operating system abstraction, were demonstrated as a mechanism for controlling secondary resources such as files and the file system.