1 /*
2  * Copyright (C) 2023 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.systemui.util
18 
19 /**
20  * A collection of listeners, observers, callbacks, etc.
21  *
22  * This container is optimized for infrequent mutation and frequent iteration, with thread safety
23  * and reentrant-safety guarantees as well. Specifically, to ensure that
24  * [ConcurrentModificationException] is never thrown, this iterator will not reflect changes made to
25  * the set after the iterator is constructed.
26  */
27 interface IListenerSet<E : Any> : Set<E> {
28     /**
29      * A thread-safe, reentrant-safe method to add a listener. Does nothing if the listener is
30      * already in the set.
31      */
addIfAbsentnull32     fun addIfAbsent(element: E): Boolean
33 
34     /** A thread-safe, reentrant-safe method to remove a listener. */
35     fun remove(element: E): Boolean
36 }
37