Wednesday, March 4, 2009

Why JNode?

There seems to be a certain confusion in the community about the motivation of the JNode project and specifically the unusual choice of the Java language for implementing it. I think some explanation is necessary.

JNode is an operating system based on Java technology. Its implementation language is Java because this is the standard language of the Java platform. The Java language has many advantages (as being type safe, relatively readable ) but many of the advantages come from the Java byte code and the Java virtual machine. JNode is not based on the Java platform for the sake of writing it in the Java language as some people might think. One of the most important points of JNode is that the overwhelming majority of its code is compiled to and executed as Java byte code in a safe environment. JNode aims to achieve increased stability, robustness, reliability and performance by choosing the Java byte code as executable code format and executing it within an appropriate virtual machine. The past one and a half decade demonstrated the superior runtime characteristics and reliability of the Java byte code based programs compared to native programs. Moreover this has proven to be so successful that practically the mainstream domains of application software development have largely adopted the execution model where the program translated to a more or less safe byte code run within a dedicated virtual machine. It's among the goals of JNode to extend this model to the complete software stack including the operating system. By JNode itself being translated to Java byte code which is also its primary executable code format, JNode is a metacircular execution environment with respect to the Java byte code This has deep implications regarding future capabilities which can be built into the system and combined with the dynamic, flexible and object oriented nature of the Java byte code opens perspectives to solutions which are impossible or hard to implement in traditional operating systems. Reflection, manageability, dynamic profiling, byte code instrumentation, dynamic class reloading, to mention a couple of remarkable properties of Java code, extended to the level of the whole system and applied by the system to itself opens the road towards self-managing, adaptive, self-inspecting, self-diagnosing and self-healing capabilities in JNode. Here the point is to gather the information from the running system, that is usually gathered by a human operator from a well tooled Java application today, automatically feed it back to the system in a meaningful way and then let the system make appropriate decisions and take actions based on that information.

The JNode operating system internally is based on a virtual machine specially developed for this purpose. This virtual machine takes care of running its own code as well as the code of the rest of the JNode operating system and the applications running on top of it. Sharing of code and resources is maximized among all components and layers of the system. JNode has a flat memory model and protection is based on the inherent safety and type-safety of the Java byte code and the built-in security of the system. These characteristics eliminate the need for context switching and native interface. The executable code is byte code managed by the system-wide unique virtual machine, compiled to native code dynamically with the possibility to make advanced optimization across layers of the system impossible to achieve in the traditional dichotomy of a statically compiled native operating system with statically compiled platform specific native Java virtual machine running on top of it. In JNode the overhead of starting a new Java application can be largely reduced due to the fact that most of the resources needed to run the application have already been set up, warmed up and are ready to be reused within the operating system itself.

JNode also aims to provide an outstanding platform for running Java applications. JNode is a platform created from the ground up by Java programmers with Java tools and Java technology specially for running Java programs. Java programs are currently run on many platforms but on all platforms very often they look & feel like somewhat foreign citizens. Any enthusiast of a particular platform will tell it and most of them will avoid Java and make choices specific to that platform for their tasks. This situation is most visible in desktop use-cases and command line based utilities. In contrast with this, a Java program on JNode is the native program of the platform.

So these are just a couple of ideas to demonstrate that JNode is not being developed simply because 'Java is cool' and 'pure Java' is a supreme value in itself sufficiently compelling to build an operating system around it. JNode by taking the unique path of creating a complete Java program execution environment starting from the most fundamental operating system services up to the application level based on the Java technology itself aims to explore and extend the powerful capabilities of the Java platform to the level of a whole completely standalone and self-sufficient software system and staring from this foundation explore new holistic possibilities in a self-contained, high performance, safe, secure still flexible and dynamic self-managing, adaptive systems design. JNode is not about the Java based development of a Java virtual machine, device driver, JIT compiler, thread scheduler, memory manager or any other particular component of a software system. JNode is about the development of the combination of all these based on the powerful capabilities of the Java platform using a metacircular approach. The focus of JNode is the whole not the part.

1 comment:

Denis Washington said...

A very interesting post. I would recommend you to put this information on the JNode homepage somewhere; many in an About section?