| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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 org.apache.hadoop.hdfs.util; |
| |
| import java.lang.ref.WeakReference; |
| import java.nio.ByteBuffer; |
| import java.util.Queue; |
| import java.util.concurrent.ConcurrentHashMap; |
| import java.util.concurrent.ConcurrentLinkedQueue; |
| import java.util.concurrent.ConcurrentMap; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| |
| import com.google.common.annotations.VisibleForTesting; |
| |
| /** |
| * A simple class for pooling direct ByteBuffers. This is necessary |
| * because Direct Byte Buffers do not take up much space on the heap, |
| * and hence will not trigger GCs on their own. However, they do take |
| * native memory, and thus can cause high memory usage if not pooled. |
| * The pooled instances are referred to only via weak references, allowing |
| * them to be collected when a GC does run. |
| * |
| * This class only does effective pooling when many buffers will be |
| * allocated at the same size. There is no attempt to reuse larger |
| * buffers to satisfy smaller allocations. |
| */ |
| @InterfaceAudience.Private |
| public class DirectBufferPool { |
| |
| // Essentially implement a multimap with weak values. |
| ConcurrentMap<Integer, Queue<WeakReference<ByteBuffer>>> buffersBySize = |
| new ConcurrentHashMap<Integer, Queue<WeakReference<ByteBuffer>>>(); |
| |
| /** |
| * Allocate a direct buffer of the specified size, in bytes. |
| * If a pooled buffer is available, returns that. Otherwise |
| * allocates a new one. |
| */ |
| public ByteBuffer getBuffer(int size) { |
| Queue<WeakReference<ByteBuffer>> list = buffersBySize.get(size); |
| if (list == null) { |
| // no available buffers for this size |
| return ByteBuffer.allocateDirect(size); |
| } |
| |
| WeakReference<ByteBuffer> ref; |
| while ((ref = list.poll()) != null) { |
| ByteBuffer b = ref.get(); |
| if (b != null) { |
| return b; |
| } |
| } |
| |
| return ByteBuffer.allocateDirect(size); |
| } |
| |
| /** |
| * Return a buffer into the pool. After being returned, |
| * the buffer may be recycled, so the user must not |
| * continue to use it in any way. |
| * @param buf the buffer to return |
| */ |
| public void returnBuffer(ByteBuffer buf) { |
| buf.clear(); // reset mark, limit, etc |
| int size = buf.capacity(); |
| Queue<WeakReference<ByteBuffer>> list = buffersBySize.get(size); |
| if (list == null) { |
| list = new ConcurrentLinkedQueue<WeakReference<ByteBuffer>>(); |
| Queue<WeakReference<ByteBuffer>> prev = buffersBySize.putIfAbsent(size, list); |
| // someone else put a queue in the map before we did |
| if (prev != null) { |
| list = prev; |
| } |
| } |
| list.add(new WeakReference<ByteBuffer>(buf)); |
| } |
| |
| /** |
| * Return the number of available buffers of a given size. |
| * This is used only for tests. |
| */ |
| @VisibleForTesting |
| int countBuffersOfSize(int size) { |
| Queue<WeakReference<ByteBuffer>> list = buffersBySize.get(size); |
| if (list == null) { |
| return 0; |
| } |
| |
| return list.size(); |
| } |
| } |