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Re: Classpath build process and VM-specific issues

From: Archie Cobbs
Subject: Re: Classpath build process and VM-specific issues
Date: Mon, 29 Mar 2004 08:42:17 -0600
User-agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.6) Gecko/20040312

Andrew Haley wrote:
 > > > I would like the vmdata field type then to be VMClass not Object.
> > > > I disagree, as it imposes a restriction on what vmData actually
 > > is.  The most obvious implementation of vmData is to be a byte[]
 > > instance holding the byte of a native pointer to an internal VM
 > > non-moveable data structure.
> > I'm glad to see we agree (although I don't think it's at all obvious
 > that it should be a byte[], not all VMs use native code).

Eeeh.  I can't imagine that either.  If there's a strong argument for
holding native pointer in a byte[] ?

Here's my thinking on this topic. Warning: may not apply to you :-)

Object is good because it is automatically the size of a pointer
on any platform. However, it has one significant disadvantage, which
is that you must special case all such fields in your garbage collector
(unless you have a conservative collector). byte[] avoids this problem.

I remember kaffe had a kaffe.util.Pointer reference type that did this,
and was specially recognized by the GC. Slightly better than Object imho.


Archie Cobbs      *        CTO, Awarix        *

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