| /* |
| * Copyright (C) 2021 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 androidx.window.util; |
| |
| import androidx.annotation.GuardedBy; |
| import androidx.annotation.NonNull; |
| |
| import java.util.HashSet; |
| import java.util.LinkedHashSet; |
| import java.util.Optional; |
| import java.util.Set; |
| import java.util.function.Consumer; |
| |
| /** |
| * Base class that provides the implementation for the callback mechanism of the |
| * {@link DataProducer} API. This class is thread safe for adding, removing, and notifying |
| * consumers. |
| * |
| * @param <T> The type of data this producer returns through {@link DataProducer#getData}. |
| */ |
| public abstract class BaseDataProducer<T> implements DataProducer<T>, |
| AcceptOnceConsumer.AcceptOnceProducerCallback<T> { |
| |
| private final Object mLock = new Object(); |
| @GuardedBy("mLock") |
| private final Set<Consumer<T>> mCallbacks = new LinkedHashSet<>(); |
| @GuardedBy("mLock") |
| private final Set<Consumer<T>> mCallbacksToRemove = new HashSet<>(); |
| |
| /** |
| * Adds a callback to the set of callbacks listening for data. Data is delivered through |
| * {@link BaseDataProducer#notifyDataChanged(Object)}. This method is thread safe. Callers |
| * should ensure that callbacks are thread safe. |
| * @param callback that will receive data from the producer. |
| */ |
| @Override |
| public final void addDataChangedCallback(@NonNull Consumer<T> callback) { |
| synchronized (mLock) { |
| mCallbacks.add(callback); |
| } |
| Optional<T> currentData = getCurrentData(); |
| currentData.ifPresent(callback); |
| onListenersChanged(); |
| } |
| |
| /** |
| * Removes a callback to the set of callbacks listening for data. This method is thread safe |
| * for adding. |
| * @param callback that was registered in |
| * {@link BaseDataProducer#addDataChangedCallback(Consumer)}. |
| */ |
| @Override |
| public final void removeDataChangedCallback(@NonNull Consumer<T> callback) { |
| synchronized (mLock) { |
| mCallbacks.remove(callback); |
| } |
| onListenersChanged(); |
| } |
| |
| /** |
| * Returns {@code true} if there are any registered callbacks {@code false} if there are no |
| * registered callbacks. |
| */ |
| // TODO(b/278132889) Improve the structure of BaseDataProdcuer while avoiding known issues. |
| public final boolean hasListeners() { |
| synchronized (mLock) { |
| return !mCallbacks.isEmpty(); |
| } |
| } |
| |
| protected void onListenersChanged() {} |
| |
| /** |
| * @return the current data if available and {@code Optional.empty()} otherwise. |
| */ |
| @NonNull |
| public abstract Optional<T> getCurrentData(); |
| |
| /** |
| * Called to notify all registered consumers that the data provided |
| * by {@link DataProducer#getData} has changed. Calls to this are thread save but callbacks need |
| * to ensure thread safety. |
| */ |
| protected void notifyDataChanged(T value) { |
| synchronized (mLock) { |
| for (Consumer<T> callback : mCallbacks) { |
| callback.accept(value); |
| } |
| removeFinishedCallbacksLocked(); |
| } |
| } |
| |
| /** |
| * Removes any callbacks that notified us through {@link #onConsumerReadyToBeRemoved(Consumer)} |
| * that they are ready to be removed. |
| */ |
| @GuardedBy("mLock") |
| private void removeFinishedCallbacksLocked() { |
| for (Consumer<T> callback: mCallbacksToRemove) { |
| mCallbacks.remove(callback); |
| } |
| mCallbacksToRemove.clear(); |
| } |
| |
| @Override |
| public void onConsumerReadyToBeRemoved(Consumer<T> callback) { |
| synchronized (mLock) { |
| mCallbacksToRemove.add(callback); |
| } |
| } |
| } |