From: Peter Suk <peter.kwangjun.suk@...>
Date: 2005-04-09T03:09:34+09:00
Subject: Re: Seven new VMs, all in a row

On Apr 8, 2005, at 12:39 PM, Charles Mills wrote:

> Peter Suk wrote:
>> Generational GC.  (So you're not at the mercy of the system's malloc
> &
>> free)
>
> A generational GC would be great.  There has been talk of including one
> in the next version of the Ruby interpreter.  However C extensions also
> pose a problem here as well - it seems creating a write barrier that
> works with C libraries not written originally with Ruby in mind will be
> very difficult/slow.

VisualWorks gets around this and also solves problems the paradox with 
not having "real" threads, wanting to do GC efficently, yet also 
wanting to do synchronous calls to the OS.  The dilemma is this: You 
want real threads so your VM can utilize synchronous calls to the OS.  
However, this complicates GC immensely.  (ObjectStudio Smalltalk lost a 
lot of performance because of having real threads.  When it was time to 
GC, the main VM thread would have to raise a flag and wait for all the 
other threads to detect it.)

VisualWorks can use real threads, but only in the case of calling out 
to a DLL, and these contexts are exempt from GC.  This gives you the 
ability to make synchronous calls without freezing the entire image, 
yet also leaves your GC simple and fast.

--Peter

--
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