GDBM.php

   1 <?php
   2
   3   // GDBM class with live compression
   4
   5 class GDBM {
   6
   7   var $oldfile;                 // The name of the "Old" file
   8   var $newfile;                 // The name of the "New" file
   9   var $oldr;                    // Resource pointer for $oldfile
  10   var $newr;                    // Resource pointer for $newfile
  11   var $copycount;               // Number of keys to copy per access
  12   var $error;                   // error string for last operation
  13
  14   function GDBM($oldfile, $newfile, $copycount=20, $handler="gdbm") {
  15     $this->oldfile = $oldfile;
  16     $this->newfile = $newfile;
  17     $this->copycount = $copycount;
  18     $this->handler = $handler;
  19
  20     $oldr = dba_open($oldfile, 'cl', $handler);
  21
  22     if (!$oldr) {
  23       $this->error = "Could not open old database";
  24       return;
  25     }
  26
  27     $this->oldr = $oldr;
  28
  29     if ($newfile == '') {
  30       $this->newfile = false;
  31       $this->newr = false;
  32     } else {
  33       if (file_exists($newfile)) {
  34         $this->newr = dba_open($newfile, 'wl', $handler);
  35       } else $this->newr = false;
  36     }
  37   }
  38
  39   // Get the value for a key.
  40   // If it's in the new database, return that value.
  41   // If the deleted key is in the new database, return false.
  42   // Otherwise, return the value in the old databae.
  43   function get($key) {
  44     $value = false;
  45     if ($this->newr) {
  46       $this->copysome(true);
  47       if ($this->newr) $value = dba_fetch($key, $this->newr);
  48     }
  49     if (!$value) $value = dba_fetch($key, $this->oldr);
  50     return $value;
  51   }
  52
  53   // Replace or set the value of $key to $value.
  54   // If $value is blank or false, delete $key from the database
  55   // Return the new value
  56   function put($key, $value) {
  57     if ($value == '' || !$value) {
  58       // Blank or false value = delete the key
  59       dba_delete($key, $this->oldr);
  60       if ($this->newr) {
  61         dba_delete($key, $this->newr);
  62         $this->copysome(true);
  63       }
  64     } else {
  65       if ($this->newr) {
  66         dba_replace($key, $value, $this->newr);
  67         dba_delete($key, $this->oldr);
  68         $this->copysome(true);
  69       } else {
  70         dba_replace($key, $value, $this->oldr);
  71       }
  72     }
  73     return $value;
  74   }
  75
  76   // Create a new database, if there isn't one, and start copying to it
  77   function startCopying() {
  78     if (!$this->newr && $this->newfile) {
  79       $this->newr = dba_open($this->newfile, 'cl', $this->handler);
  80     }
  81     return $this->newr;
  82   }
  83
  84   // True if we're currently copying old to new
  85   function isCopying() {
  86     return $this->newr;
  87   }
  88
  89   // Finish copying old to new, delete old, rename new to old, and reopen
  90   // Do NOT start copying again.
  91   function finishCopying() {
  92     while ($this->newr) $this->copysome(false);
  93   }
  94
  95   // Close the database(s). Finish copying first if $finish_copying is true
  96   function close($finish_copying=false) {
  97     if ($finish_copying) $this->finishCopying();
  98     if ($this->oldr) {
  99       dba_close($this->oldr);
 100       $this->oldr = false;
 101     }
 102     if ($this->newr) {
 103       dba_close($this->newr);
 104       $this->newr = false;
 105     }
 106   }
 107
 108   // Reopen the database after a close.
 109   // Does nothing if alredy open
 110   function reopen() {
 111     if (!$this->oldr) {
 112       $this->oldr = dba_open($this->oldfile, 'wl', $this->handler);
 113       if (!$this->oldr) $this->error = "Could not reopen old file";
 114     }
 115     return $this->oldr;
 116   }
 117
 118   // Return the message for the last error that happened, and clear it
 119   function errorMessage() {
 120     $res = $this->error;
 121     $this->error = '';
 122     return $res;
 123   }
 124
 125   // Copy $this->copycount keys from old to new database
 126   function copysome($reopen) {
 127     if ($this->newr) {
 128       for ($i=0; $i<$this->copycount; $i++) {
 129         $key = dba_firstkey($this->oldr);
 130         if ($key) $this->copyone($key);
 131         else {
 132           // We're done copying.
 133           $this->flipDBs($reopen);
 134           return;
 135         }
 136       }
 137     }
 138   }
 139
 140   // Copy one key from old to new database
 141   function copyone($key) {
 142     if ($this->newr) {
 143       if (!dba_fetch($key, $this->newr)) {
 144         $value = dba_fetch($key, $this->oldr);
 145         if ($value) dba_replace($key, $value, $this->newr);
 146       }
 147       dba_delete($key, $this->oldr);
 148     }
 149   }
 150
 151   // Delete the old database, and rename new to old
 152   function flipDBs($reopen) {
 153     $this->close(false);
 154     $oldsize = filesize($this->oldfile);
 155     $newsize = filesize($this->newfile);
 156     $this->error = "old size: $oldsize, new size: $newsize";
 157     if (unlink($this->oldfile)) {
 158       if (rename($this->newfile, $this->oldfile)) {
 159         if ($reopen) $this->reopen();
 160       } else $this->error = "Could not rename new file to old file";
 161     } else $this->error = "Could not unlink old file";
 162   }
 163
 164 }
 165
 166 // Test code. Uncomment to run.
 167 /*
 168 if (file_exists('old.db')) unlink('old.db');
 169 if (file_exists('new.db')) unlink('new.db');
 170 $db = new GDBM('old.db', 'new.db', 1);
 171 $cnt = 99;
 172 $loops = 10;
 173 for ($i=1; $i<=$cnt; $i++) {
 174   $db->put($i, $i);
 175 }
 176 $db->startCopying();
 177 for ($j=0; $j<$loops; $j++) {
 178   for ($i=1; $i<=$cnt; $i++) {
 179     if (($j % 2) == 1 && ($i % 10) == 3) $db->put($i, '');
 180     else $db->put($i, 10 * $db->get($i));
 181     if (!$db->isCopying()) {
 182       echo "Restarting copying, j=$j, i=$i\n";
 183       echo "  " . $db->errorMessage() . "\n";
 184       $db->startCopying();
 185     }
 186   }
 187 }
 188 for ($i=1; $i<=$cnt; $i++) {
 189   echo "$i: " . $db->get($i) . "\n";
 190   if (!$db->isCopying()) $db->startCopying();
 191 }
 192 $db->close(true);
 193 */
 194
 195 // Copyright 2008 Bill St. Clair
 196 //
 197 // Licensed under the Apache License, Version 2.0 (the "License");
 198 // you may not use this file except in compliance with the License.
 199 // You may obtain a copy of the License at
 200 //
 201 //     http://www.apache.org/licenses/LICENSE-2.0
 202 //
 203 // Unless required by applicable law or agreed to in writing, software
 204 // distributed under the License is distributed on an "AS IS" BASIS,
 205 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 206 // See the License for the specific language governing permissions
 207 // and limitations under the License.
 208
 209 ?>