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authorBobby Georgescu <georgescu@google.com>2013-05-21 12:08:06 -0700
committerBobby Georgescu <georgescu@google.com>2013-05-21 15:18:18 -0700
commit6b9ece8710604adec2805b903d977264f90087c6 (patch)
tree6d1e77e408026df172f481feb4461b41273f11ab /src/com/android/photos
parent90529c8c1634c35f39033397c6196922d797ea67 (diff)
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Add comments to bitmap pools
Change-Id: Ie841316629ef0737dcdd5002b3278cf0bca3a768
Diffstat (limited to 'src/com/android/photos')
-rw-r--r--src/com/android/photos/data/GalleryBitmapPool.java37
-rw-r--r--src/com/android/photos/data/SparseArrayBitmapPool.java74
2 files changed, 105 insertions, 6 deletions
diff --git a/src/com/android/photos/data/GalleryBitmapPool.java b/src/com/android/photos/data/GalleryBitmapPool.java
index a5a17ede2..7eb9794c5 100644
--- a/src/com/android/photos/data/GalleryBitmapPool.java
+++ b/src/com/android/photos/data/GalleryBitmapPool.java
@@ -23,9 +23,25 @@ import android.util.Pools.SimplePool;
import com.android.photos.data.SparseArrayBitmapPool.Node;
+/**
+ * Pool allowing the efficient reuse of bitmaps in order to avoid long
+ * garbage collection pauses.
+ */
public class GalleryBitmapPool {
private static final int CAPACITY_BYTES = 20971520;
+
+ // We found that Gallery uses bitmaps that are either square (for example,
+ // tiles of large images or square thumbnails), match one of the common
+ // photo aspect ratios (4x3, 3x2, or 16x9), or, less commonly, are of some
+ // other aspect ratio. Taking advantage of this information, we use 3
+ // SparseArrayBitmapPool instances to back the GalleryBitmapPool, which affords
+ // O(1) lookups for square bitmaps, and average-case - but *not* asymptotically -
+ // O(1) lookups for common photo aspect ratios and other miscellaneous aspect
+ // ratios. Beware of the pathological case where there are many bitmaps added
+ // to the pool with different non-square aspect ratios but the same width, as
+ // performance will degrade and the average case lookup will approach
+ // O(# of different aspect ratios).
private static final int POOL_INDEX_NONE = -1;
private static final int POOL_INDEX_SQUARE = 0;
private static final int POOL_INDEX_PHOTO = 1;
@@ -84,11 +100,20 @@ public class GalleryBitmapPool {
return POOL_INDEX_MISC;
}
+ /**
+ * @return Capacity of the pool in bytes.
+ */
public synchronized int getCapacity() {
return mCapacityBytes;
}
- public synchronized int getSize() {
+ /**
+ * @return Approximate total size in bytes of the bitmaps stored in the pool.
+ */
+ public int getSize() {
+ // Note that this only returns an approximate size, since multiple threads
+ // might be getting and putting Bitmaps from the pool and we lock at the
+ // sub-pool level to avoid unnecessary blocking.
int total = 0;
for (SparseArrayBitmapPool p : mPools) {
total += p.getSize();
@@ -96,6 +121,9 @@ public class GalleryBitmapPool {
return total;
}
+ /**
+ * @return Bitmap from the pool with the desired height/width or null if none available.
+ */
public Bitmap get(int width, int height) {
SparseArrayBitmapPool pool = getPoolForDimensions(width, height);
if (pool == null) {
@@ -105,6 +133,10 @@ public class GalleryBitmapPool {
}
}
+ /**
+ * Adds the given bitmap to the pool.
+ * @return Whether the bitmap was added to the pool.
+ */
public boolean put(Bitmap b) {
if (b == null || b.getConfig() != Bitmap.Config.ARGB_8888) {
return false;
@@ -118,6 +150,9 @@ public class GalleryBitmapPool {
}
}
+ /**
+ * Empty the pool, recycling all the bitmaps currently in it.
+ */
public void clear() {
for (SparseArrayBitmapPool p : mPools) {
p.clear();
diff --git a/src/com/android/photos/data/SparseArrayBitmapPool.java b/src/com/android/photos/data/SparseArrayBitmapPool.java
index 1ef9e9f48..95e10267b 100644
--- a/src/com/android/photos/data/SparseArrayBitmapPool.java
+++ b/src/com/android/photos/data/SparseArrayBitmapPool.java
@@ -20,10 +20,15 @@ import android.graphics.Bitmap;
import android.util.SparseArray;
import android.util.Pools.Pool;
+import android.util.Pools.SimplePool;
+/**
+ * Bitmap pool backed by a sparse array indexing linked lists of bitmaps
+ * sharing the same width. Performance will degrade if using this to store
+ * many bitmaps with the same width but many different heights.
+ */
public class SparseArrayBitmapPool {
- private static final int BITMAPS_TO_KEEP_AFTER_UNNEEDED_HINT = 4;
private int mCapacityBytes;
private SparseArray<Node> mStore = new SparseArray<Node>();
private int mSizeBytes = 0;
@@ -34,53 +39,80 @@ public class SparseArrayBitmapPool {
protected static class Node {
Bitmap bitmap;
+
+ // Each node is part of two doubly linked lists:
+ // - A pool-level list (accessed by mPoolNodesHead and mPoolNodesTail)
+ // that is used for FIFO eviction of nodes when the pool gets full.
+ // - A bucket-level list for each index of the sparse array, so that
+ // each index can store more than one item.
Node prevInBucket;
Node nextInBucket;
Node nextInPool;
Node prevInPool;
}
+ /**
+ * @param capacityBytes Maximum capacity of the pool in bytes.
+ * @param nodePool Shared pool to use for recycling linked list nodes, or null.
+ */
public SparseArrayBitmapPool(int capacityBytes, Pool<Node> nodePool) {
mCapacityBytes = capacityBytes;
- mNodePool = nodePool;
+ if (nodePool == null) {
+ mNodePool = new SimplePool<Node>(32);
+ } else {
+ mNodePool = nodePool;
+ }
}
+ /**
+ * Set the maximum capacity of the pool, and if necessary trim it down to size.
+ */
public synchronized void setCapacity(int capacityBytes) {
mCapacityBytes = capacityBytes;
+
+ // No-op unless current size exceeds the new capacity.
freeUpCapacity(0);
}
private void freeUpCapacity(int bytesNeeded) {
int targetSize = mCapacityBytes - bytesNeeded;
+ // Repeatedly remove the oldest node until we have freed up at least bytesNeeded.
while (mPoolNodesTail != null && mSizeBytes > targetSize) {
unlinkAndRecycleNode(mPoolNodesTail, true);
}
}
private void unlinkAndRecycleNode(Node n, boolean recycleBitmap) {
- // Remove the node from its spot in its bucket
+ // Unlink the node from its sparse array bucket list.
if (n.prevInBucket != null) {
+ // This wasn't the head, update the previous node.
n.prevInBucket.nextInBucket = n.nextInBucket;
} else {
+ // This was the head of the bucket, replace it with the next node.
mStore.put(n.bitmap.getWidth(), n.nextInBucket);
}
if (n.nextInBucket != null) {
+ // This wasn't the tail, update the next node.
n.nextInBucket.prevInBucket = n.prevInBucket;
}
- // Remove the node from its spot in the list of pool nodes
+ // Unlink the node from the pool-wide list.
if (n.prevInPool != null) {
+ // This wasn't the head, update the previous node.
n.prevInPool.nextInPool = n.nextInPool;
} else {
+ // This was the head of the pool-wide list, update the head pointer.
mPoolNodesHead = n.nextInPool;
}
if (n.nextInPool != null) {
+ // This wasn't the tail, update the next node.
n.nextInPool.prevInPool = n.prevInPool;
} else {
+ // This was the tail, update the tail pointer.
mPoolNodesTail = n.prevInPool;
}
- // Recycle the node
+ // Recycle the node.
n.nextInBucket = null;
n.nextInPool = null;
n.prevInBucket = null;
@@ -91,16 +123,29 @@ public class SparseArrayBitmapPool {
mNodePool.release(n);
}
+ /**
+ * @return Capacity of the pool in bytes.
+ */
public synchronized int getCapacity() {
return mCapacityBytes;
}
+ /**
+ * @return Total size in bytes of the bitmaps stored in the pool.
+ */
public synchronized int getSize() {
return mSizeBytes;
}
+ /**
+ * @return Bitmap from the pool with the desired height/width or null if none available.
+ */
public synchronized Bitmap get(int width, int height) {
Node cur = mStore.get(width);
+
+ // Traverse the list corresponding to the width bucket in the
+ // sparse array, and unlink and return the first bitmap that
+ // also has the correct height.
while (cur != null) {
if (cur.bitmap.getHeight() == height) {
Bitmap b = cur.bitmap;
@@ -112,28 +157,43 @@ public class SparseArrayBitmapPool {
return null;
}
+ /**
+ * Adds the given bitmap to the pool.
+ * @return Whether the bitmap was added to the pool.
+ */
public synchronized boolean put(Bitmap b) {
if (b == null) {
return false;
}
+
+ // Ensure there is enough room to contain the new bitmap.
int bytes = b.getByteCount();
freeUpCapacity(bytes);
+
Node newNode = mNodePool.acquire();
if (newNode == null) {
newNode = new Node();
}
newNode.bitmap = b;
+
+ // We append to the head, and freeUpCapacity clears from the tail,
+ // resulting in FIFO eviction.
newNode.prevInBucket = null;
newNode.prevInPool = null;
newNode.nextInPool = mPoolNodesHead;
mPoolNodesHead = newNode;
+
+ // Insert the node into its appropriate bucket based on width.
int key = b.getWidth();
newNode.nextInBucket = mStore.get(key);
if (newNode.nextInBucket != null) {
+ // The bucket already had nodes, update the old head.
newNode.nextInBucket.prevInBucket = newNode;
}
mStore.put(key, newNode);
+
if (newNode.nextInPool == null) {
+ // This is the only node in the list, update the tail pointer.
mPoolNodesTail = newNode;
} else {
newNode.nextInPool.prevInPool = newNode;
@@ -142,7 +202,11 @@ public class SparseArrayBitmapPool {
return true;
}
+ /**
+ * Empty the pool, recycling all the bitmaps currently in it.
+ */
public synchronized void clear() {
+ // Clearing is equivalent to ensuring all the capacity is available.
freeUpCapacity(mCapacityBytes);
}
}