1 files changed, 104 insertions, 0 deletions
diff --git a/toolkit/jetpack/sdk/system/unload.js b/toolkit/jetpack/sdk/system/unload.js
new file mode 100644
index 000000000..98ab5f8f3
--- /dev/null
+++ b/toolkit/jetpack/sdk/system/unload.js
@@ -0,0 +1,104 @@
+/* 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/. */
+
+// Parts of this module were taken from narwhal:
+//
+// http://narwhaljs.org
+
+module.metadata = {
+  "stability": "experimental"
+};
+
+const { Cu } = require('chrome');
+const { on, off } = require('./events');
+const unloadSubject = require('@loader/unload');
+
+const observers = [];
+const unloaders = [];
+
+function WeakObserver(inner) {
+  this._inner = Cu.getWeakReference(inner);
+}
+
+Object.defineProperty(WeakObserver.prototype, 'value', {
+  get: function() { this._inner.get() }
+});
+
+var when = exports.when = function when(observer, opts) {
+  opts = opts || {};
+  for (var i = 0; i < observers.length; ++i) {
+    if (observers[i] === observer || observers[i].value === observer) {
+      return;
+    }
+  }
+  if (opts.weak) {
+    observers.unshift(new WeakObserver(observer));
+  } else {
+    observers.unshift(observer);
+  }
+};
+
+var ensure = exports.ensure = function ensure(obj, destructorName) {
+  if (!destructorName)
+    destructorName = "unload";
+  if (!(destructorName in obj))
+    throw new Error("object has no '" + destructorName + "' property");
+
+  let called = false;
+  let originalDestructor = obj[destructorName];
+
+  function unloadWrapper(reason) {
+    if (!called) {
+      called = true;
+      let index = unloaders.indexOf(unloadWrapper);
+      if (index == -1)
+        throw new Error("internal error: unloader not found");
+      unloaders.splice(index, 1);
+      originalDestructor.call(obj, reason);
+      originalDestructor = null;
+      destructorName = null;
+      obj = null;
+    }
+  };
+
+  // TODO: Find out why the order is inverted here. It seems that
+  // it may be causing issues!
+  unloaders.push(unloadWrapper);
+
+  obj[destructorName] = unloadWrapper;
+};
+
+function unload(reason) {
+  observers.forEach(function(observer) {
+    try {
+      if (observer instanceof WeakObserver) {
+        observer = observer.value;
+      }
+      if (typeof observer === 'function') {
+        observer(reason);
+      }
+    }
+    catch (error) {
+      console.exception(error);
+    }
+  });
+}
+
+when(function(reason) {
+  unloaders.slice().forEach(function(unloadWrapper) {
+    unloadWrapper(reason);
+  });
+});
+
+on('sdk:loader:destroy', function onunload({ subject, data: reason }) {
+  // If this loader is unload then `subject.wrappedJSObject` will be
+  // `destructor`.
+  if (subject.wrappedJSObject === unloadSubject) {
+    off('sdk:loader:destroy', onunload);
+    unload(reason);
+  }
+// Note that we use strong reference to listener here to make sure it's not
+// GC-ed, which may happen otherwise since nothing keeps reference to `onunolad`
+// function.
+}, true);