The Tor Browser / file revision

 /* 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/. */

 module.metadata = {

   "stability": "experimental"

 };

 "use strict";

 const { Cu } = require("chrome");

 function makeGetterFor(Type) {

   let cache = new WeakMap();

   return function getFor(target) {

     if (!cache.has(target))

       cache.set(target, new Type());

     return cache.get(target);

   }

 }

 let getLookupFor = makeGetterFor(WeakMap);

 let getRefsFor = makeGetterFor(Set);

 function add(target, value) {

   if (has(target, value))

     return;

   getLookupFor(target).set(value, true);

   getRefsFor(target).add(Cu.getWeakReference(value));

 }

 exports.add = add;

 function remove(target, value) {

   getLookupFor(target).delete(value);

 }

 exports.remove = remove;

 function has(target, value) {

   return getLookupFor(target).has(value);

 }

 exports.has = has;

 function clear(target) {

   getLookupFor(target).clear();

   getRefsFor(target).clear();

 }

 exports.clear = clear;

 function iterator(target) {

   let refs = getRefsFor(target);

   for (let ref of refs) {

     let value = ref.get();

     // If `value` is already gc'ed, it would be `null`.

     // The `has` function is using a WeakMap as lookup table, so passing `null`

     // would raise an exception because WeakMap accepts as value only non-null

     // object.

     // Plus, if `value` is already gc'ed, we do not have to take it in account

     // during the iteration, and remove it from the references.

     if (value !== null && has(target, value))

       yield value;

     else

       refs.delete(ref);

   }

 }

 exports.iterator = iterator;