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Diffstat (limited to 'core/src/main/java/com/android/volley/toolbox/ByteArrayPool.java')
-rw-r--r-- | core/src/main/java/com/android/volley/toolbox/ByteArrayPool.java | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/core/src/main/java/com/android/volley/toolbox/ByteArrayPool.java b/core/src/main/java/com/android/volley/toolbox/ByteArrayPool.java new file mode 100644 index 0000000..0134fa2 --- /dev/null +++ b/core/src/main/java/com/android/volley/toolbox/ByteArrayPool.java @@ -0,0 +1,130 @@ +/* + * Copyright (C) 2012 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package com.android.volley.toolbox; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.List; + +/** + * ByteArrayPool is a source and repository of <code>byte[]</code> objects. Its purpose is to supply + * those buffers to consumers who need to use them for a short period of time and then dispose of + * them. Simply creating and disposing such buffers in the conventional manner can considerable heap + * churn and garbage collection delays on Android, which lacks good management of short-lived heap + * objects. It may be advantageous to trade off some memory in the form of a permanently allocated + * pool of buffers in order to gain heap performance improvements; that is what this class does. + * + * <p>A good candidate user for this class is something like an I/O system that uses large temporary + * <code>byte[]</code> buffers to copy data around. In these use cases, often the consumer wants the + * buffer to be a certain minimum size to ensure good performance (e.g. when copying data chunks off + * of a stream), but doesn't mind if the buffer is larger than the minimum. Taking this into account + * and also to maximize the odds of being able to reuse a recycled buffer, this class is free to + * return buffers larger than the requested size. The caller needs to be able to gracefully deal + * with getting buffers any size over the minimum. + * + * <p>If there is not a suitably-sized buffer in its recycling pool when a buffer is requested, this + * class will allocate a new buffer and return it. + * + * <p>This class has no special ownership of buffers it creates; the caller is free to take a buffer + * it receives from this pool, use it permanently, and never return it to the pool; additionally, it + * is not harmful to return to this pool a buffer that was allocated elsewhere, provided there are + * no other lingering references to it. + * + * <p>This class ensures that the total size of the buffers in its recycling pool never exceeds a + * certain byte limit. When a buffer is returned that would cause the pool to exceed the limit, + * least-recently-used buffers are disposed. + */ +public class ByteArrayPool { + /** The buffer pool, arranged both by last use and by buffer size */ + private final List<byte[]> mBuffersByLastUse = new ArrayList<>(); + + private final List<byte[]> mBuffersBySize = new ArrayList<>(64); + + /** The total size of the buffers in the pool */ + private int mCurrentSize = 0; + + /** + * The maximum aggregate size of the buffers in the pool. Old buffers are discarded to stay + * under this limit. + */ + private final int mSizeLimit; + + /** Compares buffers by size */ + protected static final Comparator<byte[]> BUF_COMPARATOR = + new Comparator<byte[]>() { + @Override + public int compare(byte[] lhs, byte[] rhs) { + return lhs.length - rhs.length; + } + }; + + /** @param sizeLimit the maximum size of the pool, in bytes */ + public ByteArrayPool(int sizeLimit) { + mSizeLimit = sizeLimit; + } + + /** + * Returns a buffer from the pool if one is available in the requested size, or allocates a new + * one if a pooled one is not available. + * + * @param len the minimum size, in bytes, of the requested buffer. The returned buffer may be + * larger. + * @return a byte[] buffer is always returned. + */ + public synchronized byte[] getBuf(int len) { + for (int i = 0; i < mBuffersBySize.size(); i++) { + byte[] buf = mBuffersBySize.get(i); + if (buf.length >= len) { + mCurrentSize -= buf.length; + mBuffersBySize.remove(i); + mBuffersByLastUse.remove(buf); + return buf; + } + } + return new byte[len]; + } + + /** + * Returns a buffer to the pool, throwing away old buffers if the pool would exceed its allotted + * size. + * + * @param buf the buffer to return to the pool. + */ + public synchronized void returnBuf(byte[] buf) { + if (buf == null || buf.length > mSizeLimit) { + return; + } + mBuffersByLastUse.add(buf); + int pos = Collections.binarySearch(mBuffersBySize, buf, BUF_COMPARATOR); + if (pos < 0) { + pos = -pos - 1; + } + mBuffersBySize.add(pos, buf); + mCurrentSize += buf.length; + trim(); + } + + /** Removes buffers from the pool until it is under its size limit. */ + private synchronized void trim() { + while (mCurrentSize > mSizeLimit) { + byte[] buf = mBuffersByLastUse.remove(0); + mBuffersBySize.remove(buf); + mCurrentSize -= buf.length; + } + } +} |