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annotate src/com/tmate/hgkit/fs/DataAccessProvider.java @ 16:254078595653

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author Artem Tikhomirov <tikhomirov.artem@gmail.com>
date Mon, 27 Dec 2010 01:00:53 +0100
parents 382cfe9463db
children 6f9aca1a97be
rev   line source
10
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1 /*
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2 * Copyright (c) 2010 Artem Tikhomirov
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3 */
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4 package com.tmate.hgkit.fs;
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5
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6 import java.io.File;
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7 import java.io.FileInputStream;
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8 import java.io.IOException;
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9 import java.nio.ByteBuffer;
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10 import java.nio.MappedByteBuffer;
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11 import java.nio.channels.FileChannel;
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12
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13 /**
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14 *
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15 * @author artem
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16 */
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17 public class DataAccessProvider {
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19 private final int mapioMagicBoundary;
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20 private final int bufferSize;
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21
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22 public DataAccessProvider() {
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23 mapioMagicBoundary = 100 * 1024;
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24 bufferSize = 8 * 1024;
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25 }
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26
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27 public DataAccess create(File f) {
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28 if (!f.exists()) {
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29 return new DataAccess();
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30 }
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31 try {
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32 FileChannel fc = new FileInputStream(f).getChannel();
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33 if (fc.size() > mapioMagicBoundary) {
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34 return new MemoryMapFileAccess(fc, fc.size());
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35 } else {
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36 // XXX once implementation is more or less stable,
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37 // may want to try ByteBuffer.allocateDirect() to see
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38 // if there's any performance gain.
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39 boolean useDirectBuffer = false;
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40 return new FileAccess(fc, fc.size(), bufferSize, useDirectBuffer);
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41 }
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42 } catch (IOException ex) {
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43 // unlikely to happen, we've made sure file exists.
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44 ex.printStackTrace(); // FIXME log error
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45 }
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46 return new DataAccess(); // non-null, empty.
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47 }
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48
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49 // DOESN'T WORK YET
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50 private static class MemoryMapFileAccess extends DataAccess {
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51 private FileChannel fileChannel;
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52 private final long size;
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53 private long position = 0;
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54
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55 public MemoryMapFileAccess(FileChannel fc, long channelSize) {
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56 fileChannel = fc;
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57 size = channelSize;
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58 }
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59
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60 @Override
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61 public void seek(long offset) {
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62 position = offset;
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63 }
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64
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65 @Override
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66 public void skip(int bytes) throws IOException {
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67 position += bytes;
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68 }
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69
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70 private boolean fill() throws IOException {
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71 final int BUFFER_SIZE = 8 * 1024;
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72 long left = size - position;
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73 MappedByteBuffer rv = fileChannel.map(FileChannel.MapMode.READ_ONLY, position, left < BUFFER_SIZE ? left : BUFFER_SIZE);
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74 position += rv.capacity();
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75 return rv.hasRemaining();
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76 }
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77
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78 @Override
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79 public void done() {
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80 if (fileChannel != null) {
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81 try {
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82 fileChannel.close();
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83 } catch (IOException ex) {
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84 ex.printStackTrace(); // log debug
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85 }
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86 fileChannel = null;
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87 }
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88 }
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89 }
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90
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91 // (almost) regular file access - FileChannel and buffers.
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92 private static class FileAccess extends DataAccess {
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93 private FileChannel fileChannel;
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94 private final long size;
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95 private ByteBuffer buffer;
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96 private long bufferStartInFile = 0; // offset of this.buffer in the file.
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97
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98 public FileAccess(FileChannel fc, long channelSize, int bufferSizeHint, boolean useDirect) {
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99 fileChannel = fc;
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100 size = channelSize;
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101 final int capacity = size < bufferSizeHint ? (int) size : bufferSizeHint;
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102 buffer = useDirect ? ByteBuffer.allocateDirect(capacity) : ByteBuffer.allocate(capacity);
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103 buffer.flip(); // or .limit(0) to indicate it's empty
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104 }
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105
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106 @Override
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107 public boolean isEmpty() {
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108 return bufferStartInFile + buffer.position() >= size;
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109 }
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110
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111 @Override
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112 public void seek(long offset) throws IOException {
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113 if (offset < bufferStartInFile + buffer.limit() && offset >= bufferStartInFile) {
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114 buffer.position((int) (offset - bufferStartInFile));
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115 } else {
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116 // out of current buffer, invalidate it (force re-read)
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117 // XXX or ever re-read it right away?
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118 bufferStartInFile = offset;
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119 buffer.clear();
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120 buffer.limit(0); // or .flip() to indicate we switch to reading
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121 fileChannel.position(offset);
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122 }
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123 }
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124
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125 @Override
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126 public void skip(int bytes) throws IOException {
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127 final int newPos = buffer.position() + bytes;
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128 if (newPos >= 0 && newPos < buffer.limit()) {
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129 // no need to move file pointer, just rewind/seek buffer
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130 buffer.position(newPos);
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131 } else {
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132 //
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133 seek(fileChannel.position()+ bytes);
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134 }
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135 }
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136
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137 private boolean fill() throws IOException {
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138 if (!buffer.hasRemaining()) {
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139 bufferStartInFile += buffer.limit();
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140 buffer.clear();
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141 if (bufferStartInFile < size) { // just in case there'd be any exception on EOF, not -1
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142 fileChannel.read(buffer);
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143 // may return -1 when EOF, but empty will reflect this, hence no explicit support here
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144 }
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145 buffer.flip();
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146 }
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147 return buffer.hasRemaining();
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148 }
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149
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150 @Override
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151 public void readBytes(byte[] buf, int offset, int length) throws IOException {
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152 final int tail = buffer.remaining();
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153 if (tail >= length) {
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154 buffer.get(buf, offset, length);
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155 } else {
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156 buffer.get(buf, offset, tail);
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157 if (fill()) {
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158 buffer.get(buf, offset + tail, length - tail);
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159 } else {
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160 throw new IOException(); // shall not happen provided stream contains expected data and no attempts to read past nonEmpty() == false are made.
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161 }
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162 }
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163 }
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164
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165 @Override
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166 public byte readByte() throws IOException {
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167 if (buffer.hasRemaining()) {
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168 return buffer.get();
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169 }
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170 if (fill()) {
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171 return buffer.get();
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172 }
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173 throw new IOException();
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174 }
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175
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176 @Override
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177 public void done() {
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178 if (buffer != null) {
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179 buffer = null;
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180 }
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181 if (fileChannel != null) {
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182 try {
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183 fileChannel.close();
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184 } catch (IOException ex) {
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185 ex.printStackTrace(); // log debug
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186 }
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187 fileChannel = null;
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188 }
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189 }
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190 }
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191 }