Home | History | Annotate | Download | only in media 
      1 /*
      2  * Copyright (C) 2015 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 package com.android.messaging.datamodel.media;
     17 
     18 import android.os.SystemClock;
     19 
     20 import com.android.messaging.util.Assert;
     21 import com.android.messaging.util.LogUtil;
     22 import com.google.common.base.Throwables;
     23 
     24 import java.util.ArrayList;
     25 import java.util.concurrent.locks.ReentrantLock;
     26 
     27 /**
     28  * A ref-counted class that holds loaded media resource, be it bitmaps or media bytes.
     29  * Subclasses must implement the close() method to release any resources (such as bitmaps)
     30  * when it's no longer used.
     31  *
     32  * Instances of the subclasses are:
     33  * 1. Loaded by their corresponding MediaRequest classes.
     34  * 2. Maintained by MediaResourceManager in its MediaCache pool.
     35  * 3. Used by the UI (such as ContactIconViews) to present the content.
     36  *
     37  * Note: all synchronized methods in this class (e.g. addRef()) should not attempt to make outgoing
     38  * calls that could potentially acquire media cache locks due to the potential deadlock this can
     39  * cause. To synchronize read/write access to shared resource, {@link #acquireLock()} and
     40  * {@link #releaseLock()} must be used, instead of using synchronized keyword.
     41  */
     42 public abstract class RefCountedMediaResource {
     43     private final String mKey;
     44     private int mRef = 0;
     45     private long mLastRefAddTimestamp;
     46 
     47     // Set DEBUG to true to enable detailed stack trace for each addRef() and release() operation
     48     // to find out where each ref change happens.
     49     private static final boolean DEBUG = false;
     50     private static final String TAG = "bugle_media_ref_history";
     51     private final ArrayList<String> mRefHistory = new ArrayList<String>();
     52 
     53     // A lock that guards access to shared members in this class (and all its subclasses).
     54     private final ReentrantLock mLock = new ReentrantLock();
     55 
     56     public RefCountedMediaResource(final String key) {
     57         mKey = key;
     58     }
     59 
     60     public String getKey() {
     61         return mKey;
     62     }
     63 
     64     public void addRef() {
     65         acquireLock();
     66         try {
     67             if (DEBUG) {
     68                 mRefHistory.add("Added ref current ref = " + mRef);
     69                 mRefHistory.add(Throwables.getStackTraceAsString(new Exception()));
     70             }
     71 
     72             mRef++;
     73             mLastRefAddTimestamp = SystemClock.elapsedRealtime();
     74         } finally {
     75             releaseLock();
     76         }
     77     }
     78 
     79     public void release() {
     80         acquireLock();
     81         try {
     82             if (DEBUG) {
     83                 mRefHistory.add("Released ref current ref = " + mRef);
     84                 mRefHistory.add(Throwables.getStackTraceAsString(new Exception()));
     85             }
     86 
     87             mRef--;
     88             if (mRef == 0) {
     89                 close();
     90             } else if (mRef < 0) {
     91                 if (DEBUG) {
     92                     LogUtil.i(TAG, "Unwinding ref count history for RefCountedMediaResource "
     93                             + this);
     94                     for (final String ref : mRefHistory) {
     95                         LogUtil.i(TAG, ref);
     96                     }
     97                 }
     98                 Assert.fail("RefCountedMediaResource has unbalanced ref. Refcount=" + mRef);
     99             }
    100         } finally {
    101             releaseLock();
    102         }
    103     }
    104 
    105     public int getRefCount() {
    106         acquireLock();
    107         try {
    108             return mRef;
    109         } finally {
    110             releaseLock();
    111         }
    112     }
    113 
    114     public long getLastRefAddTimestamp() {
    115         acquireLock();
    116         try {
    117             return mLastRefAddTimestamp;
    118         } finally {
    119             releaseLock();
    120         }
    121     }
    122 
    123     public void assertSingularRefCount() {
    124         acquireLock();
    125         try {
    126             Assert.equals(1, mRef);
    127         } finally {
    128             releaseLock();
    129         }
    130     }
    131 
    132     void acquireLock() {
    133         mLock.lock();
    134     }
    135 
    136     void releaseLock() {
    137         mLock.unlock();
    138     }
    139 
    140     void assertLockHeldByCurrentThread() {
    141         Assert.isTrue(mLock.isHeldByCurrentThread());
    142     }
    143 
    144     boolean isEncoded() {
    145         return false;
    146     }
    147 
    148     boolean isCacheable() {
    149         return true;
    150     }
    151 
    152     MediaRequest<? extends RefCountedMediaResource> getMediaDecodingRequest(
    153             final MediaRequest<? extends RefCountedMediaResource> originalRequest) {
    154         return null;
    155     }
    156 
    157     MediaRequest<? extends RefCountedMediaResource> getMediaEncodingRequest(
    158             final MediaRequest<? extends RefCountedMediaResource> originalRequest) {
    159         return null;
    160     }
    161 
    162     public abstract int getMediaSize();
    163     protected abstract void close();
    164 }