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From "Geir Magnusson Jr." <ge...@apache.org>
Subject Re: The Classpath VM interface. (Please read)
Date Tue, 07 Jun 2005 12:15:49 GMT

On Jun 6, 2005, at 2:29 PM, Sven de Marothy wrote:

> Hi,
> Ok, the amount of confusion going on is just amazing.
> I'll try to recapitulate what the actual situation and actual issues
> are.
> It is of course impossible to implement a java class library  
> completely
> independently of the Virtual Machine. The VM must be able to provide
> certain basic, core things.
> Sun has not documented how their VM works with rt.jar. Therefore it is
> not possible to develop a Sun class library-compatible VM in a
> clean-room fashion.

Not *now*, but Harmony has the potential to be a long-running, far- 
reaching project, and our interest from the beginning is to have Sun  
involved.  So it's not unthinkable to assume that Sun might be  
interested in participating at some point in the future.

That doesn't mean we'll hold things up waiting, but we also can't  
assume that they'll never be interested.


> The only real issues raised so far (that I've seen), are the  
> following:
> 1) GNU Classpath's VM interface doesn't include things necessary for
> J2SE 5.
> (My take on it: There is no VM which needs them yet.)

But you absolutely know we will.

> 2) GNU Classpath's VM interface uses language protection such as
> package-privacy to hide the VM classes.
> (My take on it: Why is that a problem?)

You are misrepresenting the problem.  it's not that it's language  
protection, but that you extend java.lang namespace and are hoping  
that you don't get tromped by the spec at some point in the future.   
(Nor is it clear that it's good citizenship working in that namespace  
as well...)

> 3) If Harmony commits itself to using the Classpath VM interface, it
> won't be able to use other class libraries.
> (My take on it: The alternative being one with an undocumented
> proprietary VM interface, and .. well, what else?)

We want to be able to choose class library implementations.  We want  
to work with GNU Classpath now, and work out an independent interface  
that starts w/ GNU CLasspath, is supported [enthusiastically] by GNU  
Classpath, and one that we can evolve together with GNU Classpath.   
But just as GNU Classpath thought it wise to keep the door open for  
multiple VM implementations, we are trying to do the same for mutiple  
class library implementations.


> /Sven
> [1] http://www.gnu.org/software/classpath/docs/vmintegration.html
> [2]
> http://savannah.gnu.org/cgi-bin/viewcvs/classpath/classpath/vm/ 
> reference/java/
> [3] Apparently I was wrong about this previously, David Grove  
> corrected
> me. JikesRVM does use the Classpath VM interface.

Geir Magnusson Jr                                  +1-203-665-6437

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