/*
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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.concurrent.TimeUnit;
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import java.util.concurrent.TimeoutException;
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import javax.annotation.Nonnull;
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/**
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* Like {@link ConcurrentBufferQueue}, but also tracks the number of objects
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* currently in the queue.
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*/
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public class CountableBufferQueue<T> implements BufferQueueController<T>, BufferQueue<T> {
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private class DecrementingProcessor<T> implements
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ConcurrentBufferQueue.UnusedElementProcessor<T> {
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private final ConcurrentBufferQueue.UnusedElementProcessor mProcessor;
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private DecrementingProcessor(ConcurrentBufferQueue.UnusedElementProcessor<T> processor) {
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mProcessor = processor;
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}
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@Override
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public void process(T element) {
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mProcessor.process(element);
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decrementSize();
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}
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}
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private final ConcurrentBufferQueue<T> mBufferQueue;
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private final Object mCountLock;
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private final Updatable<Integer> mSizeCallback;
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private int mCount;
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/**
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* @param sizeCallback A thread-safe callback to be updated with the size
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* of the queue.
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* @param processor The callback for processing elements discarded from the
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* queue.
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*/
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public CountableBufferQueue(Updatable<Integer> sizeCallback, ConcurrentBufferQueue
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.UnusedElementProcessor<T> processor) {
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mBufferQueue = new ConcurrentBufferQueue<T>(new DecrementingProcessor<T>(processor));
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mCountLock = new Object();
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mCount = 0;
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mSizeCallback = sizeCallback;
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}
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public CountableBufferQueue(ConcurrentState<Integer> sizeCallback) {
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this(sizeCallback, new ConcurrentBufferQueue.UnusedElementProcessor<T>() {
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@Override
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public void process(T element) {
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// Do nothing by default.
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}
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});
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}
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private void decrementSize() {
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int count;
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synchronized (mCountLock) {
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mCount--;
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count = mCount;
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}
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mSizeCallback.update(count);
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}
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@Override
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public T getNext() throws InterruptedException, BufferQueueClosedException {
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T result = mBufferQueue.getNext();
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decrementSize();
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return result;
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}
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@Override
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public T getNext(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException,
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BufferQueueClosedException {
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T result = mBufferQueue.getNext(timeout, unit);
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decrementSize();
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return result;
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}
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@Override
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public T peekNext() {
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return mBufferQueue.peekNext();
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}
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@Override
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public void discardNext() {
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mBufferQueue.discardNext();
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}
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@Override
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public void update(@Nonnull T element) {
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// This is tricky since mBufferQueue.update() may immediately discard
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// the element if the queue is closed. Sending redundant updates for 0
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// size is acceptable, but sending updates indicating that the size has
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// increased and then decreased, even after the queue is closed, would
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// be bad. Thus, the following will filter these out.
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int preCount;
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int postCount;
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synchronized (mCountLock) {
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preCount = mCount;
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mCount++;
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mBufferQueue.update(element);
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postCount = mCount;
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}
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if (preCount != postCount) {
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mSizeCallback.update(postCount);
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}
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}
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@Override
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public void close() {
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mBufferQueue.close();
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}
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@Override
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public boolean isClosed() {
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return mBufferQueue.isClosed();
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}
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}
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