From 36d22d82aa202bb199967e9512281e9a53db42c9 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 21:33:14 +0200 Subject: Adding upstream version 115.7.0esr. Signed-off-by: Daniel Baumann --- services/common/observers.sys.mjs | 148 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 148 insertions(+) create mode 100644 services/common/observers.sys.mjs (limited to 'services/common/observers.sys.mjs') diff --git a/services/common/observers.sys.mjs b/services/common/observers.sys.mjs new file mode 100644 index 0000000000..c79b2b1bf2 --- /dev/null +++ b/services/common/observers.sys.mjs @@ -0,0 +1,148 @@ +/* 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/. */ + +/** + * A service for adding, removing and notifying observers of notifications. + * Wraps the nsIObserverService interface. + * + * @version 0.2 + */ +export var Observers = { + /** + * Register the given callback as an observer of the given topic. + * + * @param topic {String} + * the topic to observe + * + * @param callback {Object} + * the callback; an Object that implements nsIObserver or a Function + * that gets called when the notification occurs + * + * @param thisObject {Object} [optional] + * the object to use as |this| when calling a Function callback + * + * @returns the observer + */ + add(topic, callback, thisObject) { + let observer = new Observer(topic, callback, thisObject); + this._cache.push(observer); + Services.obs.addObserver(observer, topic, true); + + return observer; + }, + + /** + * Unregister the given callback as an observer of the given topic. + * + * @param topic {String} + * the topic being observed + * + * @param callback {Object} + * the callback doing the observing + * + * @param thisObject {Object} [optional] + * the object being used as |this| when calling a Function callback + */ + remove(topic, callback, thisObject) { + // This seems fairly inefficient, but I'm not sure how much better + // we can make it. We could index by topic, but we can't index by callback + // or thisObject, as far as I know, since the keys to JavaScript hashes + // (a.k.a. objects) can apparently only be primitive values. + let [observer] = this._cache.filter( + v => + v.topic == topic && v.callback == callback && v.thisObject == thisObject + ); + if (observer) { + Services.obs.removeObserver(observer, topic); + this._cache.splice(this._cache.indexOf(observer), 1); + } else { + throw new Error("Attempt to remove non-existing observer"); + } + }, + + /** + * Notify observers about something. + * + * @param topic {String} + * the topic to notify observers about + * + * @param subject {Object} [optional] + * some information about the topic; can be any JS object or primitive + * + * @param data {String} [optional] [deprecated] + * some more information about the topic; deprecated as the subject + * is sufficient to pass all needed information to the JS observers + * that this module targets; if you have multiple values to pass to + * the observer, wrap them in an object and pass them via the subject + * parameter (i.e.: { foo: 1, bar: "some string", baz: myObject }) + */ + notify(topic, subject, data) { + subject = typeof subject == "undefined" ? null : new Subject(subject); + data = typeof data == "undefined" ? null : data; + Services.obs.notifyObservers(subject, topic, data); + }, + + /** + * A cache of observers that have been added. + * + * We use this to remove observers when a caller calls |remove|. + * + * XXX This might result in reference cycles, causing memory leaks, + * if we hold a reference to an observer that holds a reference to us. + * Could we fix that by making this an independent top-level object + * rather than a property of this object? + */ + _cache: [], +}; + +function Observer(topic, callback, thisObject) { + this.topic = topic; + this.callback = callback; + this.thisObject = thisObject; +} + +Observer.prototype = { + QueryInterface: ChromeUtils.generateQI([ + "nsIObserver", + "nsISupportsWeakReference", + ]), + observe(subject, topic, data) { + // Extract the wrapped object for subjects that are one of our wrappers + // around a JS object. This way we support both wrapped subjects created + // using this module and those that are real XPCOM components. + if ( + subject && + typeof subject == "object" && + "wrappedJSObject" in subject && + "observersModuleSubjectWrapper" in subject.wrappedJSObject + ) { + subject = subject.wrappedJSObject.object; + } + + if (typeof this.callback == "function") { + if (this.thisObject) { + this.callback.call(this.thisObject, subject, data); + } else { + this.callback(subject, data); + } + } else { + // typeof this.callback == "object" (nsIObserver) + this.callback.observe(subject, topic, data); + } + }, +}; + +function Subject(object) { + // Double-wrap the object and set a property identifying the wrappedJSObject + // as one of our wrappers to distinguish between subjects that are one of our + // wrappers (which we should unwrap when notifying our observers) and those + // that are real JS XPCOM components (which we should pass through unaltered). + this.wrappedJSObject = { observersModuleSubjectWrapper: true, object }; +} + +Subject.prototype = { + QueryInterface: ChromeUtils.generateQI([]), + getScriptableHelper() {}, + getInterfaces() {}, +}; -- cgit v1.2.3