Home | History | Annotate | Download | only in async 
      1 /*
      2  * Copyright (C) 2014 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.camera.async;
     18 
     19 import java.util.concurrent.TimeUnit;
     20 import java.util.concurrent.TimeoutException;
     21 
     22 import javax.annotation.Nonnull;
     23 
     24 /**
     25  * Like {@link ConcurrentBufferQueue}, but also tracks the number of objects
     26  * currently in the queue.
     27  */
     28 public class CountableBufferQueue<T> implements BufferQueueController<T>, BufferQueue<T> {
     29     private class DecrementingProcessor<T> implements
     30             ConcurrentBufferQueue.UnusedElementProcessor<T> {
     31         private final ConcurrentBufferQueue.UnusedElementProcessor mProcessor;
     32 
     33         private DecrementingProcessor(ConcurrentBufferQueue.UnusedElementProcessor<T> processor) {
     34             mProcessor = processor;
     35         }
     36 
     37         @Override
     38         public void process(T element) {
     39             mProcessor.process(element);
     40             decrementSize();
     41         }
     42     }
     43 
     44     private final ConcurrentBufferQueue<T> mBufferQueue;
     45     private final Object mCountLock;
     46     private final Updatable<Integer> mSizeCallback;
     47     private int mCount;
     48 
     49     /**
     50      * @param sizeCallback A thread-safe callback to be updated with the size
     51      *            of the queue.
     52      * @param processor The callback for processing elements discarded from the
     53      *            queue.
     54      */
     55     public CountableBufferQueue(Updatable<Integer> sizeCallback, ConcurrentBufferQueue
     56             .UnusedElementProcessor<T> processor) {
     57         mBufferQueue = new ConcurrentBufferQueue<T>(new DecrementingProcessor<T>(processor));
     58         mCountLock = new Object();
     59         mCount = 0;
     60         mSizeCallback = sizeCallback;
     61     }
     62 
     63     public CountableBufferQueue(ConcurrentState<Integer> sizeCallback) {
     64         this(sizeCallback, new ConcurrentBufferQueue.UnusedElementProcessor<T>() {
     65             @Override
     66             public void process(T element) {
     67                 // Do nothing by default.
     68             }
     69         });
     70     }
     71 
     72     private void decrementSize() {
     73         int count;
     74         synchronized (mCountLock) {
     75             mCount--;
     76             count = mCount;
     77         }
     78         mSizeCallback.update(count);
     79     }
     80 
     81     @Override
     82     public T getNext() throws InterruptedException, BufferQueueClosedException {
     83         T result = mBufferQueue.getNext();
     84         decrementSize();
     85         return result;
     86     }
     87 
     88     @Override
     89     public T getNext(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException,
     90             BufferQueueClosedException {
     91         T result = mBufferQueue.getNext(timeout, unit);
     92         decrementSize();
     93         return result;
     94     }
     95 
     96     @Override
     97     public T peekNext() {
     98         return mBufferQueue.peekNext();
     99     }
    100 
    101     @Override
    102     public void discardNext() {
    103         mBufferQueue.discardNext();
    104     }
    105 
    106     @Override
    107     public void update(@Nonnull T element) {
    108         // This is tricky since mBufferQueue.update() may immediately discard
    109         // the element if the queue is closed. Sending redundant updates for 0
    110         // size is acceptable, but sending updates indicating that the size has
    111         // increased and then decreased, even after the queue is closed, would
    112         // be bad. Thus, the following will filter these out.
    113         int preCount;
    114         int postCount;
    115         synchronized (mCountLock) {
    116             preCount = mCount;
    117             mCount++;
    118             mBufferQueue.update(element);
    119             postCount = mCount;
    120         }
    121         if (preCount != postCount) {
    122             mSizeCallback.update(postCount);
    123         }
    124     }
    125 
    126     @Override
    127     public void close() {
    128         mBufferQueue.close();
    129     }
    130 
    131     @Override
    132     public boolean isClosed() {
    133         return mBufferQueue.isClosed();
    134     }
    135 }
    136