Re: VM images and working in the VM image

>From: tim Rowledge <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>Subject: Re: VM images and working in the VM image
>Date: Sat, 12 May 2007 20:40:16 -0700
>
>Of course objects that are instances of altered classes change; to do
>other wise would be lame.
>Methods are invoked by the gazillion during class changing package
>loads; since the loading is done by methods running how could it be
>otherwise? There's no magical stuff going on - a file is opened, the
>new code is read in, each method is compiled and installed and in use
>immediately.

I think the missing data here is:  When a class changes "shape", the old 
class gets temporarily moved (in Squeak it becomes a class with "Obsolete" 
appended to the front).  All running methods have a reference to this class, 
and thus it stays around until there are no more methods using it.  But the 
new class instantly takes over for all new messages, so in this way the 
system can change the shape of objects live without breaking running code.

It should be noted that Erlang behaves in a similar way to allow live system 
upgrades as well.

Thanks,
Jason

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