1 /* 2 * Copyright (C) 2021 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 import java.util.concurrent.CopyOnWriteArrayList 20 21 /** 22 * A collection of listeners, observers, callbacks, etc. 23 * 24 * This container is optimized for infrequent mutation and frequent iteration, with thread safety 25 * and reentrant-safety guarantees as well. 26 */ 27 class ListenerSet<E> : Iterable<E> { 28 private val listeners: CopyOnWriteArrayList<E> = CopyOnWriteArrayList() 29 30 /** 31 * A thread-safe, reentrant-safe method to add a listener. 32 * Does nothing if the listener is already in the set. 33 */ addIfAbsentnull34 fun addIfAbsent(element: E): Boolean = listeners.addIfAbsent(element) 35 36 /** 37 * A thread-safe, reentrant-safe method to remove a listener. 38 */ 39 fun remove(element: E): Boolean = listeners.remove(element) 40 41 /** 42 * Determine if the listener set is empty 43 */ 44 fun isEmpty(): Boolean = listeners.isEmpty() 45 46 /** 47 * Returns an iterator over the listeners currently in the set. Note that to ensure 48 * [ConcurrentModificationException] is never thrown, this iterator will not reflect changes 49 * made to the set after the iterator is constructed. 50 */ 51 override fun iterator(): Iterator<E> = listeners.iterator() 52 } 53 54 /** Extension to match Collection which is implemented to only be (easily) accessible in kotlin */ 55 fun <T> ListenerSet<T>.isNotEmpty(): Boolean = !isEmpty() 56