RE: [Sablevm-developer] reflection classes for constant pool and bytecode data

[John L. <je...@pi...>]

> > From: John Leuner <je...@pi...>
> > I'm working on a separate little project to compile kissme into
> > the linux kernel, this is of course completely non-portable, but
> > provides excellent opportunity for using Java as a systems-level
> > programming language, eg writing device drivers, managing memory
> > etc.
> > When combined with some clever run-time optimisation such as
> > inlining, you could get a system that performs as fast as today's 
> > monolithic kernel OSes (NT / Linux), but with all the benefits of
> > the Java language.
> 
> Maybe NT. :)  Not Linux.
> 
> Seriously, I suppose you can really crunch during optimization and
> end up with Java-derived native code that is nearly as fast as C-
> derived native code, provided:
> 
>   - You never use virtual methods.
> 
>   - Either a) you never use exceptions; or b) your native code 
>     never has to check an exception type before branching.
> 
>   - You never have to specify exact alignment or packing of a
>     structure (neither of which can be guaranteed or even
>     specified by the Java spec). Hmm... This can probably be
>     restated as: You don't need 'C'-like structure accesses at
>     all.

Let me restate that. Instead of saying you'll get a kernel "as fast" as a
C monolithic kernel, I think that the advantages of dynamic optimisation
(run-time profiling etc) and removal of a userspace/kernelspace barrier
will allow such a system to approach the overall performance of a
monolithic C kernel. 

But you're right, as long as you're using Virtual Methods, relying on
automatic GC and exceptions you won't be able to achieve the same speed. 

I didn't understand the bit about alignment and packing?
 
> This, however, does not give you much of the benefits of the Java
> language. It doesn't let you write network protocol stacks or
> device drivers, either.

Well you can write code of that kind by providing magic methods
which are compiled from assembly to provide access to raw hardware.

John Leuner