1 files changed, 75 insertions, 0 deletions
diff --git a/toolkit/jetpack/sdk/lang/weak-set.js b/toolkit/jetpack/sdk/lang/weak-set.js
new file mode 100644
index 000000000..8972602a5
--- /dev/null
+++ b/toolkit/jetpack/sdk/lang/weak-set.js
@@ -0,0 +1,75 @@
+/* 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 {
+    getFor(target) {
+      if (!cache.has(target))
+        cache.set(target, new Type());
+
+      return cache.get(target);
+    },
+    clearFor(target) {
+      return cache.delete(target)
+    }
+  }
+}
+
+var {getFor: getLookupFor, clearFor: clearLookupFor} = makeGetterFor(WeakMap);
+var {getFor: getRefsFor, clearFor: clearRefsFor} = 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) {
+  clearLookupFor(target);
+  clearRefsFor(target);
+}
+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;