/*
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* Copyright (C) 2014 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.camera.async;
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import java.util.Set;
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import java.util.concurrent.CopyOnWriteArraySet;
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import java.util.concurrent.Executor;
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import javax.annotation.CheckReturnValue;
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import javax.annotation.Nonnull;
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import javax.annotation.ParametersAreNonnullByDefault;
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/**
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* Generic asynchronous state wrapper which supports two methods of interaction:
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* polling for the latest value and listening for updates.
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*/
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@ParametersAreNonnullByDefault
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public class ConcurrentState<T> implements Updatable<T>, Observable<T> {
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private static class ExecutorListenerPair implements Runnable {
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private final Executor mExecutor;
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private final Runnable mListener;
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public ExecutorListenerPair(Executor executor, Runnable listener) {
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mExecutor = executor;
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mListener = listener;
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}
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/**
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* Runs the callback on the executor.
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*/
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@Override
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public void run() {
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mExecutor.execute(mListener);
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}
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}
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private final Set<ExecutorListenerPair> mListeners;
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private volatile T mValue;
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public ConcurrentState(T initialValue) {
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// Callbacks are typically only added and removed at startup/shutdown,
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// but {@link #update} is often called at high-frequency. So, using a
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// read-optimized data structure is appropriate here.
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mListeners = new CopyOnWriteArraySet<>();
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mValue = initialValue;
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}
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/**
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* Updates the state to the latest value, notifying all listeners.
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*/
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@Override
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public void update(T newValue) {
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mValue = newValue;
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for (ExecutorListenerPair pair : mListeners) {
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pair.run();
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}
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}
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@CheckReturnValue
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@Nonnull
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@Override
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public SafeCloseable addCallback(Runnable callback, Executor executor) {
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final ExecutorListenerPair pair = new ExecutorListenerPair(executor, callback);
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mListeners.add(pair);
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return new SafeCloseable() {
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@Override
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public void close() {
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mListeners.remove(pair);
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}
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};
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}
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/**
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* Polls for the latest value.
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*
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* @return The latest state.
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*/
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@Nonnull
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@Override
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public T get() {
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return mValue;
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}
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}
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