From 26a029d407be480d791972afb5975cf62c9360a6 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Fri, 19 Apr 2024 02:47:55 +0200 Subject: Adding upstream version 124.0.1. Signed-off-by: Daniel Baumann --- toolkit/modules/ContentDOMReference.sys.mjs | 177 ++++++++++++++++++++++++++++ 1 file changed, 177 insertions(+) create mode 100644 toolkit/modules/ContentDOMReference.sys.mjs (limited to 'toolkit/modules/ContentDOMReference.sys.mjs') diff --git a/toolkit/modules/ContentDOMReference.sys.mjs b/toolkit/modules/ContentDOMReference.sys.mjs new file mode 100644 index 0000000000..ef4896ff67 --- /dev/null +++ b/toolkit/modules/ContentDOMReference.sys.mjs @@ -0,0 +1,177 @@ +/* vim: set ts=2 sw=2 sts=2 et tw=80: */ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this file, + * You can obtain one at http://mozilla.org/MPL/2.0/. */ + +/** + * This module holds weak references to DOM elements that exist within the + * current content process, and converts them to a unique identifier that can be + * passed between processes. The identifer, if received by the same content process + * that issued it, can then be converted back into the DOM element (presuming the + * element hasn't had all of its other references dropped). + * + * The hope is that this module can eliminate the need for passing CPOW references + * between processes during runtime. + */ + +import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs"; + +const lazy = {}; + +XPCOMUtils.defineLazyServiceGetter( + lazy, + "finalizationService", + "@mozilla.org/toolkit/finalizationwitness;1", + "nsIFinalizationWitnessService" +); + +/** + * @typedef {number} ElementID + * @typedef {Object} ElementIdentifier + */ + +const FINALIZATION_TOPIC = "content-dom-reference-finalized"; + +// A WeakMap which ties finalization witness objects to the lifetime of the DOM +// nodes they're meant to witness. When the DOM node in the map key is +// finalized, the WeakMap stops holding the finalization witness in its value +// alive, which alerts our observer that the element has been destroyed. +const finalizerRoots = new WeakMap(); + +/** + * An identifier generated by ContentDOMReference is a unique pair of BrowsingContext + * ID and a numeric ID. gRegistry maps BrowsingContext's to an object with the following + * properties: + * + * IDToElement: + * A Map of IDs to WeakReference's to the elements they refer to. + * + * elementToID: + * A WeakMap from a DOM element to an ID that refers to it. + */ +var gRegistry = new WeakMap(); + +export var ContentDOMReference = { + _init() { + Services.obs.addObserver(this, FINALIZATION_TOPIC); + }, + + observe(subject, topic, data) { + if (topic !== FINALIZATION_TOPIC) { + throw new Error("Unexpected observer topic"); + } + + let identifier = JSON.parse(data); + this._revoke(identifier); + }, + + /** + * Generate and return an identifier for a given DOM element. + * + * @param {Element} element The DOM element to generate the identifier for. + * @return {ElementIdentifier} The identifier for the DOM element that can be passed between + * processes as a message. + */ + get(element) { + if (!element) { + throw new Error( + "Can't create a ContentDOMReference identifier for " + + "non-existant nodes." + ); + } + + let browsingContext = BrowsingContext.getFromWindow(element.ownerGlobal); + let mappings = gRegistry.get(browsingContext); + if (!mappings) { + mappings = { + IDToElement: new Map(), + elementToID: new WeakMap(), + }; + gRegistry.set(browsingContext, mappings); + } + + let id = mappings.elementToID.get(element); + if (id) { + // We already had this element registered, so return the pre-existing ID. + return { browsingContextId: browsingContext.id, id }; + } + + // We must be registering a new element at this point. + id = Math.random(); + mappings.elementToID.set(element, id); + mappings.IDToElement.set(id, Cu.getWeakReference(element)); + + let identifier = { browsingContextId: browsingContext.id, id }; + + finalizerRoots.set( + element, + lazy.finalizationService.make( + FINALIZATION_TOPIC, + JSON.stringify(identifier) + ) + ); + + return identifier; + }, + + /** + * Resolves an identifier back into the DOM Element that it was generated from. + * + * @param {ElementIdentifier} The identifier generated via ContentDOMReference.get for a + * DOM element. + * @return {Element} The DOM element that the identifier was generated for, or + * null if the element does not still exist. + */ + resolve(identifier) { + let browsingContext = BrowsingContext.get(identifier.browsingContextId); + let { id } = identifier; + return this._resolveIDToElement(browsingContext, id); + }, + + /** + * Removes an identifier from the registry so that subsequent attempts + * to resolve it will result in null. This is done automatically when the + * target node is GCed. + * + * @param {ElementIdentifier} The identifier to revoke, issued by ContentDOMReference.get for + * a DOM element. + */ + _revoke(identifier) { + let browsingContext = BrowsingContext.get(identifier.browsingContextId); + let { id } = identifier; + + let mappings = gRegistry.get(browsingContext); + if (!mappings) { + return; + } + + mappings.IDToElement.delete(id); + }, + + /** + * Private helper function that resolves a BrowsingContext and ID (the + * pair that makes up an identifier) to a DOM element. + * + * @param {BrowsingContext} browsingContext The BrowsingContext that was hosting + * the DOM element at the time that the identifier was generated. + * @param {ElementID} id The ID generated for the DOM element. + * + * @return {Element} The DOM element that the identifier was generated for, or + * null if the element does not still exist. + */ + _resolveIDToElement(browsingContext, id) { + let mappings = gRegistry.get(browsingContext); + if (!mappings) { + return null; + } + + let weakReference = mappings.IDToElement.get(id); + if (!weakReference) { + return null; + } + + return weakReference.get(); + }, +}; + +ContentDOMReference._init(); -- cgit v1.2.3