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/*
* Copyright (C) 2020 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.internal.inputmethod;
import android.annotation.AnyThread;
import android.annotation.NonNull;
import android.annotation.Nullable;
import com.android.internal.annotations.GuardedBy;
import java.util.ArrayList;
import java.util.concurrent.CompletableFuture;
/**
* A utility class, which works as both a factory class of a cancellation signal to cancel
* all the completable objects.
*
* <p>TODO: Make this lock-free.</p>
*/
public final class CancellationGroup {
private final Object mLock = new Object();
/**
* List of {@link CompletableFuture}, which can be used to propagate {@link #cancelAll()} to
* completable objects.
*
* <p>This will be lazily instantiated to avoid unnecessary object allocations.</p>
*/
@Nullable
@GuardedBy("mLock")
private ArrayList<CompletableFuture<?>> mFutureList = null;
@GuardedBy("mLock")
private boolean mCanceled = false;
/**
* Tries to register the given {@link CompletableFuture} into the callback list if this
* {@link CancellationGroup} is not yet cancelled.
*
* <p>If this {@link CancellationGroup} is already cancelled, then this method will immediately
* call {@link CompletableFuture#cancel(boolean)} then return {@code false}.</p>
*
* <p>When this method returns {@code true}, call {@link #unregisterFuture(CompletableFuture)}
* to remove the unnecessary object reference.</p>
*
* @param future {@link CompletableFuture} to be added to the cancellation callback list.
* @return {@code true} if the given {@code future} is added to the callback list.
* {@code false} otherwise.
*/
@AnyThread
boolean tryRegisterFutureOrCancelImmediately(@NonNull CompletableFuture<?> future) {
synchronized (mLock) {
if (mCanceled) {
future.cancel(false);
return false;
}
if (mFutureList == null) {
// Set the initial capacity to 1 with an assumption that usually there is up to 1
// on-going operation.
mFutureList = new ArrayList<>(1);
}
mFutureList.add(future);
return true;
}
}
@AnyThread
void unregisterFuture(@NonNull CompletableFuture<?> future) {
synchronized (mLock) {
if (mFutureList != null) {
mFutureList.remove(future);
}
}
}
/**
* Cancel all the completable objects created from this {@link CancellationGroup}.
*
* <p>Secondary calls will be silently ignored.</p>
*/
@AnyThread
public void cancelAll() {
synchronized (mLock) {
if (!mCanceled) {
mCanceled = true;
if (mFutureList != null) {
mFutureList.forEach(future -> future.cancel(false));
mFutureList.clear();
mFutureList = null;
}
}
}
}
/**
* @return {@code true} if {@link #cancelAll()} is already called. {@code false} otherwise.
*/
@AnyThread
public boolean isCanceled() {
synchronized (mLock) {
return mCanceled;
}
}
}
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