[lively-kernel] image persistence

Casey Ransberger casey.obrien.r at gmail.com
Thu Mar 14 02:52:52 CET 2013

Actually that paper answered a lot of questions I had about stuff that I
want to be able to do in Squeak eventually. I thought I'd read all of the
Self papers, but it looks like I missed this one. Thanks for the question,
Dave, and thanks for the answer, Robert!

On Wed, Mar 13, 2013 at 3:45 PM, David Paola <dpaola2 at gmail.com> wrote:

> Thanks both of you for your answers :-) that self paper is *exactly* what
> I am looking for.
> Happy hacking!
> --
> Dave Paola
> On Mar 12, 2013, at 6:47 PM, Robert Krahn <robert.krahn at gmail.com> wrote:
> 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 <robert.krahn at gmail.com>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 <dpaola2 at gmail.com> 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
>>> lively-kernel at hpi.uni-potsdam.de
>>> http://lists.hpi.uni-potsdam.de/listinfo/lively-kernel
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