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/* 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/. */
"use strict";
module.metadata = {
"stability": "unstable"
};
const { Cc, Ci, Cr, Cu } = require("chrome");
const { emit, on, off } = require("./core");
var observerService = Cc["@mozilla.org/observer-service;1"]
.getService(Ci.nsIObserverService);
const { ShimWaiver } = Cu.import("resource://gre/modules/ShimWaiver.jsm");
const addObserver = ShimWaiver.getProperty(observerService, "addObserver");
const removeObserver = ShimWaiver.getProperty(observerService, "removeObserver");
const { when: unload } = require("../system/unload");
// Simple class that can be used to instantiate event channel that
// implements `nsIObserver` interface. It's will is used by `observe`
// function as observer + event target. It basically proxies observer
// notifications as to it's registered listeners.
function ObserverChannel() {}
Object.freeze(Object.defineProperties(ObserverChannel.prototype, {
QueryInterface: {
value: function(iid) {
if (!iid.equals(Ci.nsIObserver) &&
!iid.equals(Ci.nsISupportsWeakReference) &&
!iid.equals(Ci.nsISupports))
throw Cr.NS_ERROR_NO_INTERFACE;
return this;
}
},
observe: {
value: function(subject, topic, data) {
emit(this, "data", {
type: topic,
target: subject,
data: data
});
}
}
}));
function observe(topic) {
let observerChannel = new ObserverChannel();
// Note: `nsIObserverService` will not hold a weak reference to a
// observerChannel (since third argument is `true`). There for if it
// will be GC-ed with all it's event listeners once no other references
// will be held.
addObserver(observerChannel, topic, true);
// We need to remove any observer added once the add-on is unloaded;
// otherwise we'll get a "dead object" exception.
// See: https://bugzilla.mozilla.org/show_bug.cgi?id=1001833
unload(() => removeObserver(observerChannel, topic));
return observerChannel;
}
exports.observe = observe;
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