1 files changed, 89 insertions, 0 deletions
diff --git a/toolkit/jetpack/sdk/core/observer.js b/toolkit/jetpack/sdk/core/observer.js
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+++ b/toolkit/jetpack/sdk/core/observer.js
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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": "experimental"
+};
+
+
+const { Cc, Ci, Cr, Cu } = require("chrome");
+const { Class } = require("./heritage");
+const { isWeak } = require("./reference");
+const method = require("../../method/core");
+
+const 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");
+
+// This is a method that will be invoked when notification observer
+// subscribed to occurs.
+const observe = method("observer/observe");
+exports.observe = observe;
+
+// Method to subscribe to the observer notification.
+const subscribe = method("observe/subscribe");
+exports.subscribe = subscribe;
+
+
+// Method to unsubscribe from the observer notifications.
+const unsubscribe = method("observer/unsubscribe");
+exports.unsubscribe = unsubscribe;
+
+
+// This is wrapper class that takes a `delegate` and produces
+// instance of `nsIObserver` which will delegate to a given
+// object when observer notification occurs.
+const ObserverDelegee = Class({
+  initialize: function(delegate) {
+    this.delegate = delegate;
+  },
+  QueryInterface: function(iid) {
+    if (!iid.equals(Ci.nsIObserver) &&
+        !iid.equals(Ci.nsISupportsWeakReference) &&
+        !iid.equals(Ci.nsISupports))
+      throw Cr.NS_ERROR_NO_INTERFACE;
+
+    return this;
+  },
+  observe: function(subject, topic, data) {
+    observe(this.delegate, subject, topic, data);
+  }
+});
+
+
+// Class that can be either mixed in or inherited from in
+// order to subscribe / unsubscribe for observer notifications.
+const Observer = Class({});
+exports.Observer = Observer;
+
+// Weak maps that associates instance of `ObserverDelegee` with
+// an actual observer. It ensures that `ObserverDelegee` instance
+// won't be GC-ed until given `observer` is.
+const subscribers = new WeakMap();
+
+// Implementation of `subscribe` for `Observer` type just registers
+// observer for an observer service. If `isWeak(observer)` is `true`
+// observer service won't hold strong reference to a given `observer`.
+subscribe.define(Observer, (observer, topic) => {
+  if (!subscribers.has(observer)) {
+    const delegee = new ObserverDelegee(observer);
+    subscribers.set(observer, delegee);
+    addObserver(delegee, topic, isWeak(observer));
+  }
+});
+
+// Unsubscribes `observer` from observer notifications for the
+// given `topic`.
+unsubscribe.define(Observer, (observer, topic) => {
+  const delegee = subscribers.get(observer);
+  if (delegee) {
+    subscribers.delete(observer);
+    removeObserver(delegee, topic);
+  }
+});