script: Use a u16 for prototype id to speed up Castable::is<T>()#44364
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Signed-off-by: webbeef <me@webbeef.org>
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It kills me a little bit to take the memory hit for every reflected object, but the speed tradeoff is undeniable. |
jdm
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Apr 25, 2026
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Castable::is<T>()callsget_dom_class()in a way that incurs a roundtrip to the JS engine andmultiple pointer indirections:
self.reflector().get_jsobject().get() -> JSObject
Object.shape -> BaseShape.clasp -> JSClass
DOMJSClass.dom_class -> DOMClass
interface_chain[depth] == ID -> bool
Since the ID doesn't change after creation of reflectors, we can instead store the ID on the reflector
and avoid most of that cost. The trick is to use a Depth First Search to generate IDs that allow a
range check for
Castable::is<T>. An example of IDs in the DFS looks like:EventTarget = 0
Node = 1
CharacterData = 2
Text = 3
CDATASection = 4
Comment = 5
ProcessingInstruction = 6
Document = 7
HTMLDocument = 8
XMLDocument = 9
Testing: Green try run at https://github.com/webbeef/servo/actions/runs/24640508040 and manual testing with general browsing.