michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: // Parts of this module were taken from narwhal:
michael@0: //
michael@0: // http://narwhaljs.org
michael@0: 
michael@0: module.metadata = {
michael@0:   "stability": "experimental"
michael@0: };
michael@0: 
michael@0: const { on, off } = require('./events');
michael@0: const unloadSubject = require('@loader/unload');
michael@0: 
michael@0: const observers = [];
michael@0: const unloaders = [];
michael@0: 
michael@0: var when = exports.when = function when(observer) {
michael@0:   if (observers.indexOf(observer) != -1)
michael@0:     return;
michael@0:   observers.unshift(observer);
michael@0: };
michael@0: 
michael@0: var ensure = exports.ensure = function ensure(obj, destructorName) {
michael@0:   if (!destructorName)
michael@0:     destructorName = "unload";
michael@0:   if (!(destructorName in obj))
michael@0:     throw new Error("object has no '" + destructorName + "' property");
michael@0: 
michael@0:   let called = false;
michael@0:   let originalDestructor = obj[destructorName];
michael@0: 
michael@0:   function unloadWrapper(reason) {
michael@0:     if (!called) {
michael@0:       called = true;
michael@0:       let index = unloaders.indexOf(unloadWrapper);
michael@0:       if (index == -1)
michael@0:         throw new Error("internal error: unloader not found");
michael@0:       unloaders.splice(index, 1);
michael@0:       originalDestructor.call(obj, reason);
michael@0:       originalDestructor = null;
michael@0:       destructorName = null;
michael@0:       obj = null;
michael@0:     }
michael@0:   };
michael@0: 
michael@0:   // TODO: Find out why the order is inverted here. It seems that
michael@0:   // it may be causing issues!
michael@0:   unloaders.push(unloadWrapper);
michael@0: 
michael@0:   obj[destructorName] = unloadWrapper;
michael@0: };
michael@0: 
michael@0: function unload(reason) {
michael@0:   observers.forEach(function(observer) {
michael@0:     try {
michael@0:       observer(reason);
michael@0:     }
michael@0:     catch (error) {
michael@0:       console.exception(error);
michael@0:     }
michael@0:   });
michael@0: }
michael@0: 
michael@0: when(function(reason) {
michael@0:   unloaders.slice().forEach(function(unloadWrapper) {
michael@0:     unloadWrapper(reason);
michael@0:   });
michael@0: });
michael@0: 
michael@0: on('sdk:loader:destroy', function onunload({ subject, data: reason }) {
michael@0:   // If this loader is unload then `subject.wrappedJSObject` will be
michael@0:   // `destructor`.
michael@0:   if (subject.wrappedJSObject === unloadSubject) {
michael@0:     off('sdk:loader:destroy', onunload);
michael@0:     unload(reason);
michael@0:   }
michael@0: // Note that we use strong reference to listener here to make sure it's not
michael@0: // GC-ed, which may happen otherwise since nothing keeps reference to `onunolad`
michael@0: // function.
michael@0: }, true);