[Vm-dev] Multiprocessing with Squeak

Igor Stasenko siguctua at gmail.com
Fri Jan 29 08:51:46 UTC 2010

On 29 January 2010 08:42, Colin Putney <cputney at wiresong.ca> wrote:
> On 2010-01-27, at 2:04 PM, Levente Uzonyi wrote:
>> Hi,
>> I had an idea a few days ago and even though I don't have the time or knowledge to try it myself, I just can't get it out of my head. The idea is to let an interpreter use two images at once. One of them is read only "fully working" image let's call it S (source), the other is empty (contains no objects), writeable, possibly generated on the fly, let's call it W (working). The vm knows if an object is in S or W by checking the object pointer. Whenever an object in S is about to be modified, a copy is created in W and all references to it are changed to the new one (which means that more than one object might have to be copied). This means a slower startup, but once all necessary objects are copied performance would be normal.
>> (This approach is similar to the way sources are handled today: the sources file is read only, new source code goes to the changes file.)
> I believe VW can do something like this - they call it "Shared Perm Space." There's a special section of memory that's immutable, not subject to garbage collection, and shared between several VM processes.
>> - combine it with HydraVM, it might give Erlang-like capabilities (cheap
>>  and fast processes)
> Well, we already have cheap and fast processes. The overhead for creating a new instance of Process and scheduling it is very low. What we lack is isolation between them. Squeak seems to be drifting in that direction, though. Islands are a good start. Josh's recent contribution of futures to the trunk are another step away from shared state concurrency.
> My sense of it is that efficient use of memory isn't the most important problem to solve at the moment. Further steps toward event-loop concurrency would be more fruitful.
Well, at some point we should start using some kind of native-based
concurrency, not just green threading.
Processes still run on top of a single object space, i.e. all objects
are equally reachable from any process since they are using
non-concurrent memory model.
Oh, nevermind, we had long talks about it in the past , lets not start
over again :)

> Colin

Best regards,
Igor Stasenko AKA sig.

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