1 | /**********************************************************************
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2 | *
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3 | * CacheMan.cpp
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4 | * Copyright (C) 2003 UNESCO
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5 | *
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6 | * A component of the Greenstone digital library software
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7 | * from the New Zealand Digital Library Project at the
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8 | * University of Waikato, New Zealand.
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9 | *
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10 | * This program is free software; you can redistribute it and/or modify
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11 | * it under the terms of the GNU General Public License as published by
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12 | * the Free Software Foundation; either version 2 of the License, or
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13 | * (at your option) any later version.
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14 | *
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15 | * This program is distributed in the hope that it will be useful,
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16 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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17 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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18 | * GNU General Public License for more details.
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19 | *
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20 | * You should have received a copy of the GNU General Public License
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21 | * along with this program; if not, write to the Free Software
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22 | * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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23 | *
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24 | *********************************************************************/
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25 |
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26 |
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27 | #include "stdafx.h"
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28 | #include "File.h"
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29 |
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30 | #include "CacheMan.h"
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31 |
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32 |
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33 | CacheManager::CacheManager()
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34 | {
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35 | maxblocks_ = 0;
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36 | }
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37 | CacheManager::CacheManager(unsigned blocksz, unsigned mxblks)
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38 | {
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39 | PRECONDITION(maxblocks_ == 0);
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40 | maxblocks_ = mxblks;
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41 | nused_ = 0;
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42 | blocksize_ = blocksz;
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43 | buff_ = new char[blocksize_*maxblocks_];
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44 | diskAddrs_ = new FileSystem::FAU_t[maxblocks_];
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45 | useCounts_ = new unsigned[maxblocks_];
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46 | theFile_ = NULL;
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47 | }
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48 | /*
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49 | * Construct a cache manager for blocks of size blocksz and mxblks buffers
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50 | */
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51 | void CacheManager::Create(unsigned blocksz, unsigned mxblks)
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52 | {
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53 | PRECONDITION(maxblocks_ == 0);
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54 | maxblocks_ = mxblks;
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55 | nused_ = 0;
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56 | blocksize_ = blocksz;
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57 | buff_ = new char[blocksize_*maxblocks_];
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58 | diskAddrs_ = new FileSystem::FAU_t[maxblocks_];
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59 | useCounts_ = new unsigned[maxblocks_];
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60 | theFile_ = NULL;
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61 | }
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62 |
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63 | //
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64 | // Connect to a CFileBase
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65 | //
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66 | void CacheManager::Connect(CFileBase* file)
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67 | {
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68 | PRECONDITION(nused_ == 0);
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69 | theFile_ = file;
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70 | }
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71 | //
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72 | // Disconnect the cache from the CFileBase
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73 | //
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74 | void CacheManager::Disconnect()
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75 | {
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76 | if (theFile_)
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77 | {
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78 | if (theFile_->IsOpen())
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79 | Flush();
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80 | }
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81 | theFile_ = NULL;
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82 | }
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83 |
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84 | void CacheManager::Erase()
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85 | {
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86 | Disconnect();
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87 | delete[] useCounts_;
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88 | delete[] diskAddrs_;
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89 | delete[] buff_;
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90 | maxblocks_ = 0;
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91 | }
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92 |
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93 |
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94 | CacheManager::~CacheManager()
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95 | {
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96 | Disconnect();
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97 | delete[] useCounts_;
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98 | delete[] diskAddrs_;
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99 | delete[] buff_;
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100 | }
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101 |
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102 | bool CacheManager::Flush()
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103 | {
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104 | PRECONDITION(theFile_ != NULL && theFile_->IsOpen());
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105 | // Because we use "write through", this is all that's necessary:
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106 | if (theFile_->Flush() == FILE_NO_ERROR)
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107 | return true;
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108 | return false;
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109 | }
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110 |
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111 | void CacheManager::Invalidate()
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112 | {
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113 | nused_ = 0;
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114 | }
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115 |
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116 | bool CacheManager::Read(FileSystem::FAU_t locn, void* dat)
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117 | {
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118 | PRECONDITION(dat != NULL);
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119 | size_t islot = AgeAndFindSlot(locn);
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120 |
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121 | if (islot == INVALID_NPOS)
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122 | {
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123 | // Not in buffer; we'll have to read it in from disk.
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124 | // Get a free slot.
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125 | if ((islot = GetFreeSlot()) == INVALID_NPOS)
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126 | return false;
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127 | diskAddrs_[islot] = locn;
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128 | if (!(theFile_->SeekTo(locn) == locn) ||
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129 | !(theFile_->Fetch(buff_ + islot*blocksize_, blocksize_) == FILE_NO_ERROR))
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130 | return false;
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131 | }
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132 | useCounts_[islot] = 0;
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133 | memcpy(dat, buff_ + islot*blocksize_, blocksize_);
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134 | return true;
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135 | }
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136 |
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137 | bool CacheManager::Write(FileSystem::FAU_t locn, void* dat)
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138 | {
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139 | PRECONDITION(dat != NULL);
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140 | PRECONDITION(theFile_->ReadyForWriting());
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141 | size_t islot = AgeAndFindSlot(locn);
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142 |
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143 | if (islot == INVALID_NPOS)
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144 | {
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145 | // Not in buffer; find a free slot.
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146 | if ((islot = GetFreeSlot()) == INVALID_NPOS)
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147 | return false;
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148 | diskAddrs_[islot] = locn;
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149 | }
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150 |
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151 | useCounts_[islot] = 0;
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152 | memcpy(buff_ + islot*blocksize_, dat, blocksize_);
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153 | if ((theFile_->SeekTo(locn) == locn) &&
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154 | (theFile_->Store(buff_ + islot*blocksize_, blocksize_) == FILE_NO_ERROR))
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155 | return true;
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156 | return false;
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157 | }
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158 |
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159 | //////////////////////////////////////////////////////////////////////////////////
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160 | // Private helper functions
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161 |
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162 | size_t CacheManager::AgeAndFindSlot(FileSystem::FAU_t locn)
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163 | {
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164 | size_t islot = INVALID_NPOS;
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165 | for (register unsigned i = 0; i < nused_; i++)
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166 | {
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167 | if (diskAddrs_[i] == locn)
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168 | islot = i;
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169 | useCounts_[i]++; // Age the blocks
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170 | }
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171 | return islot;
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172 | }
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173 |
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174 | bool CacheManager::Flush(unsigned)
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175 | {
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176 | if (theFile_->Flush() == FILE_NO_ERROR)
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177 | return true;
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178 | return false;
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179 | }
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180 |
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181 | size_t CacheManager::GetFreeSlot()
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182 | {
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183 | size_t islot;
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184 |
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185 | if (nused_ < maxblocks_)
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186 | {
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187 | islot = nused_++; // Found an unused slot.
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188 | }
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189 | else
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190 | {
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191 | // No free slots; get the Least Recently Used block
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192 | islot = LRU();
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193 |
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194 | if (theFile_->ReadyForWriting())
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195 | if (!Flush(islot))
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196 | islot = INVALID_NPOS;
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197 | }
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198 | return islot;
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199 | }
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200 |
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201 | size_t CacheManager::LRU() const
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202 | {
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203 | size_t islot = 0;
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204 | unsigned maxCount = useCounts_[0];
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205 | for (register unsigned i = 1; i < nused_; i++)
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206 | {
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207 | if (useCounts_[i] > maxCount)
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208 | {
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209 | maxCount = useCounts_[islot = i];
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210 | }
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211 | }
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212 | return islot;
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213 | }
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