[webkit-dev] about hashmap staticDOMObjects
mjs at apple.com
Wed Apr 22 14:26:49 PDT 2009
On Apr 22, 2009, at 12:27 AM, ZHOU Xiao-bo wrote:
> hi all:
> I still don't understand the purpose of the HashMap:
> static DOMObjectMap& domObjects()
> // Don't use malloc here. Calling malloc from a mark function
> can deadlock.
> static DOMObjectMap staticDOMObjects;
> return staticDOMObjects;
> what kind of DOMObjects should be stored in it? And why?
> I searched the source codes and I found that these classes below
> will do that:
> Document, Event, HTMLCollection, XMLHttpRequest, CanvasGradient,
> CanvasPattern, CanvasRenderingContext2D, DOMCoreException,
> DOMImplementation, DOMParser, EventException, History, NamedNodeMap,
> NodeFilter, NodeIterator, NodeList, Range, RangeException,
> TreeWalker, XMLHttpRequestException, XMLSerializer, Clipboard
> but what's the reason? Is it because these classes are essentially
> simple and just acting as a tool?
The hash map is to ensure that DOM wrappers are unique but created on
demand, without consuming a pointer in the underlying C++ object. For
DOM Nodes, we use a hash table in the Node's owner document, but in
the case of non-Node objects and the Document itself (which has no
owner document), we need this global hash table.
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