Btw. the most influencing work for Lively's persistency mechanism comes from Self, see the excellent paper Annotating Objects for Transport to Other Worlds <http://labs.oracle.com/self/papers/transporter_95.pdf>,
On Tue, Mar 12, 2013 at 5:34 PM, Robert Krahn <[email protected]>wrote: > Hi, Dave -- > > Thanks for the question, this is actually a really fascinating topic :) > > First, we wrote up some general information about it (that let's you > interactively try out things ;) here: > > http://lively-kernel.org/repository/webwerkstatt/documentation/Serialization-Overview.xhtml > and here: > > http://lively-kernel.org/repository/webwerkstatt/documentation/Serialization-Interface.xhtml > > I guess the "hairy" part was/is how to deal with "native" objects. JS > browser > environments introduce functions and state that are not implemented / > represented in the JS context but hidden. The DOM and DOM nodes are an > example > for that -- you cannot get or modify all the state that would be necessary > to > capture or restablish a document / world. > > The solution that we came up with and that works very well is to implement > a > general JS serializer that walks an object graph starting from root > objects. > When certain objects are encountered - e.g. DOM nodes - we make an > exception > (this is what the serialization plugins that are mentioned in the worlds > above > are for) and store not their full object representation but just "what we > need > to know". > > The creation of objects from a serialization works accordingly > create/instantiate objects + run custom init code for the "exceptions". > > The shortcomings of this approach are the following: > - On the application development level you still need to be a bit careful > what > objects you reference. Direct pointers to DOM nodes for example won't > break > the serialization but when you deserialize you need custom init logic to > make things work as expected again. > - The stored representations become big (x-xxx MBs) really quickly. > Implementing optimizations using the plugin approach is possible but > requires additional work. > > This deals with the "state" of a JS application / Lively world. Another > point > that you mention is to capture running computations. From a certain level > of > abstraction this is actually the same thing but since JS has incomplete > metprogramming capabilities (you are not able to reflect on closures, e.g.) > the "hidden state" problem comes up again. For Lively practically this has > little impact since in the "reactive" browser environment Lively don't > have to > implement a "main" function. Anyway, we dealt with the problem and came up > with a solution. I will describe that in an upcoming post. > > Please let me know if you have questions or want a more technical answer. > > Best, > Robert > > > > On Mon, Mar 11, 2013 at 5:51 PM, David Paola <[email protected]> wrote: > >> Hi lively kernel folks, >> >> I've spent the past month or so digging around in several language VMs -- >> CPython, Rubinius, Topaz, Pypy, etc in an attempt to add the equivalent of >> the original Smalltalk "snapshot" VM primitive. Obviously I have been naive. >> >> I've learned a lot, above all else that I'm not giving up. I have a >> decent, academic understanding of compilers, interpreters, VMs (and a foggy >> understanding of JITs), and was curious if anyone could clarify how the >> lively kernel serializes the world into JSON. Was this hairy? What were the >> hardest parts? >> >> I realize everyone has a full time job and can't hand-hold a newbie, so >> any direction at all would be appreciated. I tried to pick apart the Squeak >> source code but without a background in the Squeak architecture, it was >> fruitless. >> >> Thanks so much for your energy on lively kernel, I'm looking forward to >> hearing more and possibly contributing in the future. >> >> -dave >> >> More info: >> >> I realize that the "high level" idea of snapshotting a running VM >> basically involves serializing the object memory, bytecode, and instruction >> pointer, and then deserializing that on "resume". Most of the issues I'm >> encountering lead me to believe I have an incomplete understanding. >> >> -- >> Dave Paola >> >> _______________________________________________ >> lively-kernel mailing list >> [email protected] >> http://lists.hpi.uni-potsdam.de/listinfo/lively-kernel >> > >
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