1 /* 2 * Copyright (C) 2020 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.internal.inputmethod; 18 19 import android.annotation.AnyThread; 20 import android.annotation.NonNull; 21 import android.annotation.Nullable; 22 23 import com.android.internal.annotations.GuardedBy; 24 25 import java.util.ArrayList; 26 import java.util.concurrent.CompletableFuture; 27 28 /** 29 * A utility class, which works as both a factory class of a cancellation signal to cancel 30 * all the completable objects. 31 * 32 * <p>TODO: Make this lock-free.</p> 33 */ 34 public final class CancellationGroup { 35 private final Object mLock = new Object(); 36 37 /** 38 * List of {@link CompletableFuture}, which can be used to propagate {@link #cancelAll()} to 39 * completable objects. 40 * 41 * <p>This will be lazily instantiated to avoid unnecessary object allocations.</p> 42 */ 43 @Nullable 44 @GuardedBy("mLock") 45 private ArrayList<CompletableFuture<?>> mFutureList = null; 46 47 @GuardedBy("mLock") 48 private boolean mCanceled = false; 49 50 /** 51 * Tries to register the given {@link CompletableFuture} into the callback list if this 52 * {@link CancellationGroup} is not yet cancelled. 53 * 54 * <p>If this {@link CancellationGroup} is already cancelled, then this method will immediately 55 * call {@link CompletableFuture#cancel(boolean)} then return {@code false}.</p> 56 * 57 * <p>When this method returns {@code true}, call {@link #unregisterFuture(CompletableFuture)} 58 * to remove the unnecessary object reference.</p> 59 * 60 * @param future {@link CompletableFuture} to be added to the cancellation callback list. 61 * @return {@code true} if the given {@code future} is added to the callback list. 62 * {@code false} otherwise. 63 */ 64 @AnyThread tryRegisterFutureOrCancelImmediately(@onNull CompletableFuture<?> future)65 boolean tryRegisterFutureOrCancelImmediately(@NonNull CompletableFuture<?> future) { 66 synchronized (mLock) { 67 if (mCanceled) { 68 future.cancel(false); 69 return false; 70 } 71 if (mFutureList == null) { 72 // Set the initial capacity to 1 with an assumption that usually there is up to 1 73 // on-going operation. 74 mFutureList = new ArrayList<>(1); 75 } 76 mFutureList.add(future); 77 return true; 78 } 79 } 80 81 @AnyThread unregisterFuture(@onNull CompletableFuture<?> future)82 void unregisterFuture(@NonNull CompletableFuture<?> future) { 83 synchronized (mLock) { 84 if (mFutureList != null) { 85 mFutureList.remove(future); 86 } 87 } 88 } 89 90 /** 91 * Cancel all the completable objects created from this {@link CancellationGroup}. 92 * 93 * <p>Secondary calls will be silently ignored.</p> 94 */ 95 @AnyThread cancelAll()96 public void cancelAll() { 97 synchronized (mLock) { 98 if (!mCanceled) { 99 mCanceled = true; 100 if (mFutureList != null) { 101 mFutureList.forEach(future -> future.cancel(false)); 102 mFutureList.clear(); 103 mFutureList = null; 104 } 105 } 106 } 107 } 108 109 /** 110 * @return {@code true} if {@link #cancelAll()} is already called. {@code false} otherwise. 111 */ 112 @AnyThread isCanceled()113 public boolean isCanceled() { 114 synchronized (mLock) { 115 return mCanceled; 116 } 117 } 118 } 119