On Aug 17, 2006, at 7:35 AM, Rich Warren wrote:

> Can I suspend myProc and save it to disk (seperately from quitting  
> and saving the whole image)? Can I load it into different objects  
> and resume it? Can I sneaker net it to a different machine and load  
> it in a completely different copy of Squeak? Or will bad things  
> happen?

In theory, yes, you can. A Process is just objects, and if you  
reconstruct those objects in another Squeak image exactly as they are  
here, it should resume just fine. In practice, however, it's  
difficult to get it to work.

One of the issues is getting all the objects you need. A Process is  
basically a linked list of activation contexts (stack frames). You  
can walk that list and do whatever you like with the contexts - this  
is how Seaside implements continuations, for example. So lets say  
you're serializing them to disk. Each context contains references to  
its local variables, so you've got to serialize those as well. And of  
couse, those objects have their own internal states and references to  
other objects. Activation contexts also refer to the CompiledMethods  
that are being executed, so you've got to make sure they get  
serialized, along with all their literal objects. Often those  
literals include classes, with all *their* compiled methods... once  
all those objects are included in your serialization, you're likely  
to have the entire image.

You might take a few shortcuts, like just including stubs that stand  
in for CompiledMethods, so you can hook them up to their equivalent  
versions when you rematerialize the process in the new image. In that  
case, though, there's the risk that the new image won't be quite like  
the old one, and there will be a different version of the method  
present, or it might be missing all together. In that case the  
process wouldn't be able to resume properly.

So again, in theory possible, in practice difficult. Gets easier if  
you can narrow the scope of what you want to do - Projects are a good  
example of this.

> As a quick experiment, I tried to "save and quit" squeak while I  
> had a suspended process. Squeak locked up completely. I only tried  
> it once, however. So that may have just been a bit of random  
> misfortune. But it's the only time squeak has ever locked up on me.

Beats me. There should be no problem saving Squeak with a suspended  
process, though.

Colin