Hi,
I'm working on embedding WebKit in Smalltalk (initially
VisualWorks, probably also GST). I'm not aiming at the common embedded-
browser use-cases. Instead the aim is to use WebKit as a UI toolkit in
the same way that you would use Cocoa/Win32/GTK e.g. rather than your
code having a reference to a text editing field, you have a reference
to an 'INPUT' DOM node. I've got a few blog posts that go into more
detail if anyone is interested: (there is a question at the end of
this email, after the explanation of what I'm trying to do)
http://www.cincomsmalltalk.com/userblogs/antony/blogView?showComments=true&printTitle=WebInspector_for_WebKit_in_VW,_and_some_points_about_using_WebKit_as_a_replacement_GUI.&entry=3375921297
http://www.cincomsmalltalk.com/userblogs/antony/blogView?showComments=true&printTitle=Integrating_Gecko/Webkit_into_VisualWorks&entry=3374769328
This work relies on a seamless integration of the Smalltalk garbage
collection, which uses an generational tracing collector, with the
WebKit reference counting system. It is theoretically possible to do
this without requiring the programmer to handle the WebKit reference
counting to avoid cycles, using a mechanism I outline here:
http://www.cincomsmalltalk.com/userblogs/antony/blogView?showComments=true&printTitle=A_seamless_integration_of_VWs_tracing_collector_with_WebKits_reference_counting.&entry=3377387320
My question is how to best do the tracing within WebKit. Considering
first a purely DOM-based solution i.e. ignoring javascript - if I have
a WebKit object reference, what is the best way to trace the tree and
find all reachable objects? Specifically I need to get to all my
Smalltalk proxies. For efficiency purposes I need to keep track of
what objects have already been visited in a given gc pass. Ideally
every WebKit object would have a 2 bit colour (3 colours are needed to
avoid a flag-reset pass, and 4 colors make the new-node code easier)
but I could handle this using a per-pass identity set. The API
abstraction I'm looking for is something like:
<...>.visit(<color>, <callback>)
Which needs to be defined for every object that can be referenced from
Smalltalk.
Does anyone have any suggestions about the best way to do this? A
principal concern is that if I have to add a tracing method to every
class that introduces reference members then merging with new WebKit
releases will be a real PITA.
A related question is about threading - I've noticed with the
integration I have so far that events are all handled on the primary
thread (as I would have expected), but does any GC-significant
mutation occur on secondary threads? Can I assume a single threaded
mutator abstraction?
IMO this facility would not only be generally useful for other
language integration e.g. I'm considering Gambit or Chicken (Scheme)
integration, but would also enable a tracing collector for WebKit
itself.
Antony Blakey
--------------------------
CTO, Linkuistics Pty Ltd
Ph: 0438 840 787
What can be done with fewer [assumptions] is done in vain with more
-- William of Ockham (ca. 1285-1349)
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