Contextualizing the VM environment?
cputney at wiresong.ca
Fri Apr 14 16:49:06 UTC 2006
On Apr 13, 2006, at 4:53 PM, Ian Piumarta wrote:
> Hi Andreas,
>> What would happen if we changed the VM so that we fetch the
>> specialObjects array from the active process? In other words, each
>> process could potentially carry its own VM environment which
>> effectively describes its own variant of the VM state. With the
>> effect being that different processes could potentially have
>> different versions of class SmallInteger etc.
>> The basic question here is: Can you guys see any reason why this
>> *wouldn't* work? Is there anything I'm overlooking? Any situations
>> in which this would cause problems while (say) interrupt
>> processing or somesuch?
> The spirit of this I like a lot.
> A few things off the top of my head... The VM caches some objects
> for speed (nil, true, false) that you'd have to reload at process
> switch. You still wouldn't have complete isolation of the VM
> internals between processes. They'd all have to agree on the
> processor scheduler (or keep activeProcess apart from it); the
> formats of the splObj classes couldn't change too much (changes in
> splObjs do not affect the assumptions in the way primitive access
> fixed fields -- or you could make the primitive table process-local
> too ;-); compact classes would have to be the same (or non-
> overlapping) for any pair of processes that share instances;
> semaphores would have to be reloaded at process switch unless you
> admit the possibility of some processes hijacking interrupts, low
> space, etc. from the installed handlers.
> Of course, the correct solution is to get rid of the VM entirely.
> (By assuming the splObjs subsume the interesting aspects of VM
> internals and then making them process-local, you are essentially
> trying to pull most of the VM implementation up into userland with
> per-process granularity on customisation of its behaviour.)
I have a question along the lines of Ian's observation above. How
does this idea differ from what you proposed after Craig posted his
1337 image a while back? (http://lists.squeakfoundation.org/pipermail/
squeak-dev/2006-January/099832.html) In both cases, you're talking
about, essentially, a VM instance per Process. Is this another
approach to the same idea, or is there a key difference that I'm
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