UnrefedBitmapCache.java revision 93a35b93dc582e38ff8ee5979754a16b4bf4da0c 
1/*
2 * Copyright (C) 2013 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
17package com.android.bitmap;
18
19import android.util.Log;
20import android.util.LruCache;
21
22import com.android.bitmap.DecodeTask.Request;
23import com.android.bitmap.ReusableBitmap.NullReusableBitmap;
24import com.android.bitmap.util.Trace;
25
26/**
27 * This subclass provides custom pool behavior. The pool can be set to block on {@link #poll()} if
28 * nothing can be returned. This is useful if you know you will incur high costs upon receiving
29 * nothing from the pool, and you do not want to incur those costs at the critical moment when the
30 * UI is animating.
31 *
32 * This subclass provides custom cache behavior. Null values can be cached. Later,
33 * when the same key is used to retrieve the value, a {@link NullReusableBitmap} singleton will
34 * be returned.
35 */
36public class UnrefedBitmapCache extends UnrefedPooledCache<Request, ReusableBitmap>
37        implements BitmapCache {
38    private boolean mBlocking = false;
39    private final Object mLock = new Object();
40
41    private LruCache<Request, NullReusableBitmap> mNullRequests;
42
43    private final static boolean DEBUG = false;
44    private final static String TAG = UnrefedBitmapCache.class.getSimpleName();
45
46    public UnrefedBitmapCache(final int targetSizeBytes, final float nonPooledFraction,
47            final int nullCapacity) {
48        super(targetSizeBytes, nonPooledFraction);
49
50        if (nullCapacity > 0) {
51            mNullRequests = new LruCache<Request, NullReusableBitmap>(nullCapacity);
52        }
53    }
54
55    /**
56     * Declare that {@link #poll()} should now block until it can return something.
57     */
58    @Override
59    public void setBlocking(final boolean blocking) {
60        synchronized (mLock) {
61            if (DEBUG) {
62                Log.d(TAG, String.format("AltBitmapCache: block %b", blocking));
63            }
64            mBlocking = blocking;
65            if (!mBlocking) {
66                // no longer blocking. Notify every thread.
67                mLock.notifyAll();
68            }
69        }
70    }
71
72    @Override
73    protected int sizeOf(final ReusableBitmap value) {
74        return value.getByteCount();
75    }
76
77    /**
78     * If {@link #setBlocking(boolean)} has been called with true, this method will block until a
79     * resource is available.
80     * @return an available resource, or null if none are available. Null will never be returned
81     * until blocking is set to false.
82     */
83    @Override
84    public ReusableBitmap poll() {
85        ReusableBitmap bitmap;
86        synchronized (mLock) {
87            while ((bitmap = super.poll()) == null && mBlocking) {
88                if (DEBUG) {
89                    Log.d(TAG, String.format(
90                            "AltBitmapCache: %s waiting", Thread.currentThread().getName()));
91                }
92                Trace.beginSection("sleep");
93                try {
94                    // block
95                    mLock.wait();
96                    if (DEBUG) {
97                        Log.d(TAG, String.format("AltBitmapCache: %s notified",
98                                Thread.currentThread().getName()));
99                    }
100                } catch (InterruptedException ignored) {
101                }
102                Trace.endSection();
103            }
104        }
105        return bitmap;
106    }
107
108    @Override
109    public void offer(final ReusableBitmap value) {
110        synchronized (mLock) {
111            super.offer(value);
112            if (DEBUG) {
113                Log.d(TAG, "AltBitmapCache: offer +1");
114            }
115            // new resource gained. Notify one thread.
116            mLock.notify();
117        }
118    }
119
120    @Override
121    public ReusableBitmap get(final Request key, final boolean incrementRefCount) {
122        if (mNullRequests != null && mNullRequests.get(key) != null) {
123            return NullReusableBitmap.getInstance();
124        }
125        return super.get(key, incrementRefCount);
126    }
127
128    /**
129     * Note: The cache only supports same-sized bitmaps.
130     */
131    @Override
132    public ReusableBitmap put(final Request key, final ReusableBitmap value) {
133        if (mNullRequests != null && (value == null || value == NullReusableBitmap.getInstance())) {
134            mNullRequests.put(key, NullReusableBitmap.getInstance());
135            return null;
136        }
137
138        return super.put(key, value);
139    }
140}
141