overview
The virtual machine
At the lowest layer of rheise.os is the root virtual machine. It has the
following responsibilities:
-
host multiple lightweight Java Virtual Machines
-
facilitate interaction between Java Virtual Machines
The root virtual machine takes on the responsibility of executing and switching
threads, defining classes and enforcing type safety for all lightweight
JVMs. Since it is responsible for defining all classes, it is able
to determine when different JVMs are loading the same classes, and share
the common segments in memory. This significantly reduces the memory requirements
of each lightweight JVM.
A layered view of rheise.os is shown below:
Lightweight Java Virtual Machines
JVM
(process 1) |
JVM
(process 2) |
JVM
(process 3) |
... |
|
Root virtual machine
-
Thread switching
-
Resource control
|
-
Bytecode translation
-
I/O abstraction
|
-
Memory management
-
Persistence
|
|
| Hardware |
In order to facilitate JVM interaction, the root virtual machine employs
an extended type system that supports type compatibility between JVMs.
For example, if the root virtual machine determines class X in JVM(1)
to be compatible with class Y in JVM(2), it will allow a cast from type
X to type Y. Within each JVM however, the type system has exactly the same
behaviour as the Java type system. The type system used by the root virtual
machine is the basis for efficient interprocess communication in rheise.os.
The operating system
The major components of the operating system are executed in bytecode above
the root virtual machine. Each component is contained in its own JVM, and
can interact with other system components through various forms of IPC
enabled by the root virtual machine's type system.
In rheise.os, each JVM represents a process. The processes that make
up a running system are shown below:
Java processes
Applications
| Application 1 |
Application 2 |
Application n ... |
|
Services
| Security |
Networking |
Windowing system |
Service n ... |
|
Kernel
-
Process management
-
Kernel modules
| Disk driver |
Video driver |
Keyboard driver |
Module n ... |
|
|
|
In this diagram, each application, service, and the kernel, is a process.
The kernel also contains modules, such as device drivers. These are not
run in separate processes, but are loaded into separate class loaders within
the kernel process. This enables them to be reloaded by the kernel at runtime.