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package org.apache.lucene.index;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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/* Class that Posting and PostingVector use to write byte
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* streams into shared fixed-size byte[] arrays. The idea
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* is to allocate slices of increasing lengths For
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* example, the first slice is 5 bytes, the next slice is
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* 14, etc. We start by writing our bytes into the first
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* 5 bytes. When we hit the end of the slice, we allocate
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* the next slice and then write the address of the new
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* slice into the last 4 bytes of the previous slice (the
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* "forwarding address").
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* Each slice is filled with 0's initially, and we mark
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* the end with a non-zero byte. This way the methods
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* that are writing into the slice don't need to record
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* its length and instead allocate a new slice once they
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* hit a non-zero byte. */
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import java.util.Arrays;
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import java.util.List;
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import static org.apache.lucene.util.RamUsageEstimator.NUM_BYTES_OBJECT_REF;
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import org.apache.lucene.util.ArrayUtil;
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final class ByteBlockPool {
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abstract static class Allocator {
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abstract void recycleByteBlocks(byte[][] blocks, int start, int end);
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abstract void recycleByteBlocks(List<byte[]> blocks);
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abstract byte[] getByteBlock();
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public byte[][] buffers = new byte[10][];
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int bufferUpto = -1; // Which buffer we are upto
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public int byteUpto = DocumentsWriter.BYTE_BLOCK_SIZE; // Where we are in head buffer
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public byte[] buffer; // Current head buffer
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public int byteOffset = -DocumentsWriter.BYTE_BLOCK_SIZE; // Current head offset
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private final Allocator allocator;
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public ByteBlockPool(Allocator allocator) {
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this.allocator = allocator;
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if (bufferUpto != -1) {
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// We allocated at least one buffer
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for(int i=0;i<bufferUpto;i++)
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// Fully zero fill buffers that we fully used
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Arrays.fill(buffers[i], (byte) 0);
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// Partial zero fill the final buffer
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Arrays.fill(buffers[bufferUpto], 0, byteUpto, (byte) 0);
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// Recycle all but the first buffer
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allocator.recycleByteBlocks(buffers, 1, 1+bufferUpto);
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// Re-use the first buffer
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public void nextBuffer() {
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if (1+bufferUpto == buffers.length) {
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byte[][] newBuffers = new byte[ArrayUtil.oversize(buffers.length+1,
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NUM_BYTES_OBJECT_REF)][];
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System.arraycopy(buffers, 0, newBuffers, 0, buffers.length);
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buffer = buffers[1+bufferUpto] = allocator.getByteBlock();
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byteOffset += DocumentsWriter.BYTE_BLOCK_SIZE;
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public int newSlice(final int size) {
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if (byteUpto > DocumentsWriter.BYTE_BLOCK_SIZE-size)
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final int upto = byteUpto;
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buffer[byteUpto-1] = 16;
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// Size of each slice. These arrays should be at most 16
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// elements (index is encoded with 4 bits). First array
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// is just a compact way to encode X+1 with a max. Second
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// array is the length of each slice, ie first slice is 5
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// bytes, next slice is 14 bytes, etc.
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final static int[] nextLevelArray = {1, 2, 3, 4, 5, 6, 7, 8, 9, 9};
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final static int[] levelSizeArray = {5, 14, 20, 30, 40, 40, 80, 80, 120, 200};
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final static int FIRST_LEVEL_SIZE = levelSizeArray[0];
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public int allocSlice(final byte[] slice, final int upto) {
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final int level = slice[upto] & 15;
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final int newLevel = nextLevelArray[level];
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final int newSize = levelSizeArray[newLevel];
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// Maybe allocate another block
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if (byteUpto > DocumentsWriter.BYTE_BLOCK_SIZE-newSize)
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final int newUpto = byteUpto;
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final int offset = newUpto + byteOffset;
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// Copy forward the past 3 bytes (which we are about
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// to overwrite with the forwarding address):
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buffer[newUpto] = slice[upto-3];
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buffer[newUpto+1] = slice[upto-2];
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buffer[newUpto+2] = slice[upto-1];
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// Write forwarding address at end of last slice:
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slice[upto-3] = (byte) (offset >>> 24);
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slice[upto-2] = (byte) (offset >>> 16);
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slice[upto-1] = (byte) (offset >>> 8);
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slice[upto] = (byte) offset;
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buffer[byteUpto-1] = (byte) (16|newLevel);