Java tutorial
/** * Copyright The Apache Software Foundation * * 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.hbase.util; import java.nio.ByteBuffer; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.util.StringUtils; /** * This class manages an array of ByteBuffers with a default size 4MB. These * buffers are sequential and could be considered as a large buffer.It supports * reading/writing data from this large buffer with a position and offset */ @InterfaceAudience.Private public final class ByteBufferArray { static final Log LOG = LogFactory.getLog(ByteBufferArray.class); static final int DEFAULT_BUFFER_SIZE = 4 * 1024 * 1024; private ByteBuffer buffers[]; private Lock locks[]; private int bufferSize; private int bufferCount; /** * We allocate a number of byte buffers as the capacity. In order not to out * of the array bounds for the last byte(see {@link ByteBufferArray#multiple}), * we will allocate one additional buffer with capacity 0; * @param capacity total size of the byte buffer array * @param directByteBuffer true if we allocate direct buffer */ public ByteBufferArray(long capacity, boolean directByteBuffer) { this.bufferSize = DEFAULT_BUFFER_SIZE; if (this.bufferSize > (capacity / 16)) this.bufferSize = (int) roundUp(capacity / 16, 32768); this.bufferCount = (int) (roundUp(capacity, bufferSize) / bufferSize); LOG.info("Allocating buffers total=" + StringUtils.byteDesc(capacity) + ", sizePerBuffer=" + StringUtils.byteDesc(bufferSize) + ", count=" + bufferCount + ", direct=" + directByteBuffer); buffers = new ByteBuffer[bufferCount + 1]; locks = new Lock[bufferCount + 1]; for (int i = 0; i <= bufferCount; i++) { locks[i] = new ReentrantLock(); if (i < bufferCount) { buffers[i] = directByteBuffer ? ByteBuffer.allocateDirect(bufferSize) : ByteBuffer.allocate(bufferSize); } else { buffers[i] = ByteBuffer.allocate(0); } } } private long roundUp(long n, long to) { return ((n + to - 1) / to) * to; } /** * Transfers bytes from this buffer array into the given destination array * @param start start position in the ByteBufferArray * @param len The maximum number of bytes to be written to the given array * @param dstArray The array into which bytes are to be written * @return number of bytes read */ public int getMultiple(long start, int len, byte[] dstArray) { return getMultiple(start, len, dstArray, 0); } /** * Transfers bytes from this buffer array into the given destination array * @param start start offset of this buffer array * @param len The maximum number of bytes to be written to the given array * @param dstArray The array into which bytes are to be written * @param dstOffset The offset within the given array of the first byte to be * written * @return number of bytes read */ public int getMultiple(long start, int len, byte[] dstArray, int dstOffset) { multiple(start, len, dstArray, dstOffset, new Visitor() { public void visit(ByteBuffer bb, byte[] array, int arrayIdx, int len) { bb.get(array, arrayIdx, len); } }); return len; } /** * Transfers bytes from the given source array into this buffer array * @param start start offset of this buffer array * @param len The maximum number of bytes to be read from the given array * @param srcArray The array from which bytes are to be read */ public void putMultiple(long start, int len, byte[] srcArray) { putMultiple(start, len, srcArray, 0); } /** * Transfers bytes from the given source array into this buffer array * @param start start offset of this buffer array * @param len The maximum number of bytes to be read from the given array * @param srcArray The array from which bytes are to be read * @param srcOffset The offset within the given array of the first byte to be * read */ public void putMultiple(long start, int len, byte[] srcArray, int srcOffset) { multiple(start, len, srcArray, srcOffset, new Visitor() { public void visit(ByteBuffer bb, byte[] array, int arrayIdx, int len) { bb.put(array, arrayIdx, len); } }); } private interface Visitor { /** * Visit the given byte buffer, if it is a read action, we will transfer the * bytes from the buffer to the destination array, else if it is a write * action, we will transfer the bytes from the source array to the buffer * @param bb byte buffer * @param array a source or destination byte array * @param arrayOffset offset of the byte array * @param len read/write length */ void visit(ByteBuffer bb, byte[] array, int arrayOffset, int len); } /** * Access(read or write) this buffer array with a position and length as the * given array. Here we will only lock one buffer even if it may be need visit * several buffers. The consistency is guaranteed by the caller. * @param start start offset of this buffer array * @param len The maximum number of bytes to be accessed * @param array The array from/to which bytes are to be read/written * @param arrayOffset The offset within the given array of the first byte to * be read or written * @param visitor implement of how to visit the byte buffer */ void multiple(long start, int len, byte[] array, int arrayOffset, Visitor visitor) { assert len >= 0; long end = start + len; int startBuffer = (int) (start / bufferSize), startOffset = (int) (start % bufferSize); int endBuffer = (int) (end / bufferSize), endOffset = (int) (end % bufferSize); assert array.length >= len + arrayOffset; assert startBuffer >= 0 && startBuffer < bufferCount; assert endBuffer >= 0 && endBuffer < bufferCount || (endBuffer == bufferCount && endOffset == 0); if (startBuffer >= locks.length || startBuffer < 0) { String msg = "Failed multiple, start=" + start + ",startBuffer=" + startBuffer + ",bufferSize=" + bufferSize; LOG.error(msg); throw new RuntimeException(msg); } int srcIndex = 0, cnt = -1; for (int i = startBuffer; i <= endBuffer; ++i) { Lock lock = locks[i]; lock.lock(); try { ByteBuffer bb = buffers[i]; if (i == startBuffer) { cnt = bufferSize - startOffset; if (cnt > len) cnt = len; bb.limit(startOffset + cnt).position(startOffset); } else if (i == endBuffer) { cnt = endOffset; bb.limit(cnt).position(0); } else { cnt = bufferSize; bb.limit(cnt).position(0); } visitor.visit(bb, array, srcIndex + arrayOffset, cnt); srcIndex += cnt; } finally { lock.unlock(); } } assert srcIndex == len; } }