includes/objectcache/DBABagOStuff.php

   1 <?php
   2 /**
   3  * Object caching using DBA backend.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Cache
  22  */
  23
  24 /**
  25  * Cache that uses DBA as a backend.
  26  * Slow due to the need to constantly open and close the file to avoid holding
  27  * writer locks. Intended for development use only,  as a memcached workalike
  28  * for systems that don't have it.
  29  *
  30  * On construction you can pass array( 'dir' => '/some/path' ); as a parameter
  31  * to override the default DBA files directory (wfTempDir()).
  32  *
  33  * @ingroup Cache
  34  */
  35 class DBABagOStuff extends BagOStuff {
  36         var $mHandler, $mFile, $mReader, $mWriter, $mDisabled;
  37
  38         /**
  39          * @param $params array
  40          */
  41         public function __construct( $params ) {
  42                 global $wgDBAhandler;
  43
  44                 if ( !isset( $params['dir'] ) ) {
  45                         $params['dir'] = wfTempDir();
  46                 }
  47
  48                 $this->mFile = $params['dir'] . '/mw-cache-' . wfWikiID() . '.db';
  49                 wfDebug( __CLASS__ . ": using cache file {$this->mFile}\n" );
  50                 $this->mHandler = $wgDBAhandler;
  51         }
  52
  53         /**
  54          * Encode value and expiry for storage
  55          * @param $value
  56          * @param $expiry
  57          *
  58          * @return string
  59          */
  60         protected function encode( $value, $expiry ) {
  61                 # Convert to absolute time
  62                 $expiry = $this->convertExpiry( $expiry );
  63
  64                 return sprintf( '%010u', intval( $expiry ) ) . ' ' . serialize( $value );
  65         }
  66
  67         /**
  68          * @param $blob string
  69          * @return array list containing value first and expiry second
  70          */
  71         protected function decode( $blob ) {
  72                 if ( !is_string( $blob ) ) {
  73                         return array( false, 0 );
  74                 } else {
  75                         return array(
  76                                 unserialize( substr( $blob, 11 ) ),
  77                                 intval( substr( $blob, 0, 10 ) )
  78                         );
  79                 }
  80         }
  81
  82         /**
  83          * @return resource
  84          */
  85         protected function getReader() {
  86                 if ( file_exists( $this->mFile ) ) {
  87                         $handle = dba_open( $this->mFile, 'rl', $this->mHandler );
  88                 } else {
  89                         $handle = $this->getWriter();
  90                 }
  91
  92                 if ( !$handle ) {
  93                         wfDebug( "Unable to open DBA cache file {$this->mFile}\n" );
  94                 }
  95
  96                 return $handle;
  97         }
  98
  99         /**
 100          * @return resource
 101          */
 102         protected function getWriter() {
 103                 $handle = dba_open( $this->mFile, 'cl', $this->mHandler );
 104
 105                 if ( !$handle ) {
 106                         wfDebug( "Unable to open DBA cache file {$this->mFile}\n" );
 107                 }
 108
 109                 return $handle;
 110         }
 111
 112         /**
 113          * @param $key string
 114          * @param $casToken[optional] mixed
 115          * @return mixed
 116          */
 117         public function get( $key, &$casToken = null ) {
 118                 wfProfileIn( __METHOD__ );
 119                 wfDebug( __METHOD__ . "($key)\n" );
 120
 121                 $handle = $this->getReader();
 122                 if ( !$handle ) {
 123                         wfProfileOut( __METHOD__ );
 124                         return false;
 125                 }
 126
 127                 $val = dba_fetch( $key, $handle );
 128                 $casToken = $val;
 129                 list( $val, $expiry ) = $this->decode( $val );
 130
 131                 # Must close ASAP because locks are held
 132                 dba_close( $handle );
 133
 134                 if ( $val !== false && $expiry && $expiry < time() ) {
 135                         # Key is expired, delete it
 136                         $handle = $this->getWriter();
 137                         dba_delete( $key, $handle );
 138                         dba_close( $handle );
 139                         wfDebug( __METHOD__ . ": $key expired\n" );
 140                         $val = false;
 141                 }
 142
 143                 wfProfileOut( __METHOD__ );
 144
 145                 return $val;
 146         }
 147
 148         /**
 149          * @param $key string
 150          * @param $value mixed
 151          * @param $exptime int
 152          * @return bool
 153          */
 154         public function set( $key, $value, $exptime = 0 ) {
 155                 wfProfileIn( __METHOD__ );
 156                 wfDebug( __METHOD__ . "($key)\n" );
 157
 158                 $blob = $this->encode( $value, $exptime );
 159
 160                 $handle = $this->getWriter();
 161                 if ( !$handle ) {
 162                         wfProfileOut( __METHOD__ );
 163                         return false;
 164                 }
 165
 166                 $ret = dba_replace( $key, $blob, $handle );
 167                 dba_close( $handle );
 168
 169                 wfProfileOut( __METHOD__ );
 170                 return $ret;
 171         }
 172
 173         /**
 174          * @param $casToken mixed
 175          * @param $key string
 176          * @param $value mixed
 177          * @param $exptime int
 178          * @return bool
 179          */
 180         public function cas( $casToken, $key, $value, $exptime = 0 ) {
 181                 wfProfileIn( __METHOD__ );
 182                 wfDebug( __METHOD__ . "($key)\n" );
 183
 184                 $blob = $this->encode( $value, $exptime );
 185
 186                 $handle = $this->getWriter();
 187                 if ( !$handle ) {
 188                         wfProfileOut( __METHOD__ );
 189                         return false;
 190                 }
 191
 192                 // DBA is locked to any other write connection, so we can safely
 193                 // compare the current & previous value before saving new value
 194                 $val = dba_fetch( $key, $handle );
 195                 if ( $casToken !== $val ) {
 196                         dba_close( $handle );
 197                         wfProfileOut( __METHOD__ );
 198                         return false;
 199                 }
 200
 201                 $ret = dba_replace( $key, $blob, $handle );
 202                 dba_close( $handle );
 203
 204                 wfProfileOut( __METHOD__ );
 205                 return $ret;
 206         }
 207
 208         /**
 209          * @param $key string
 210          * @param $time int
 211          * @return bool
 212          */
 213         public function delete( $key, $time = 0 ) {
 214                 wfProfileIn( __METHOD__ );
 215                 wfDebug( __METHOD__ . "($key)\n" );
 216
 217                 $handle = $this->getWriter();
 218                 if ( !$handle ) {
 219                         wfProfileOut( __METHOD__ );
 220                         return false;
 221                 }
 222
 223                 $ret = !dba_exists( $key, $handle ) || dba_delete( $key, $handle );
 224                 dba_close( $handle );
 225
 226                 wfProfileOut( __METHOD__ );
 227                 return $ret;
 228         }
 229
 230         /**
 231          * @param $key string
 232          * @param $value mixed
 233          * @param $exptime int
 234          * @return bool
 235          */
 236         public function add( $key, $value, $exptime = 0 ) {
 237                 wfProfileIn( __METHOD__ );
 238
 239                 $blob = $this->encode( $value, $exptime );
 240
 241                 $handle = $this->getWriter();
 242
 243                 if ( !$handle ) {
 244                         wfProfileOut( __METHOD__ );
 245                         return false;
 246                 }
 247
 248                 $ret = dba_insert( $key, $blob, $handle );
 249
 250                 # Insert failed, check to see if it failed due to an expired key
 251                 if ( !$ret ) {
 252                         list( , $expiry ) = $this->decode( dba_fetch( $key, $handle ) );
 253
 254                         if ( $expiry && $expiry < time() ) {
 255                                 # Yes expired, delete and try again
 256                                 dba_delete( $key, $handle );
 257                                 $ret = dba_insert( $key, $blob, $handle );
 258                                 # This time if it failed then it will be handled by the caller like any other race
 259                         }
 260                 }
 261
 262                 dba_close( $handle );
 263
 264                 wfProfileOut( __METHOD__ );
 265                 return $ret;
 266         }
 267
 268         /**
 269          * @param $key string
 270          * @param $step integer
 271          * @return integer|bool
 272          */
 273         public function incr( $key, $step = 1 ) {
 274                 wfProfileIn( __METHOD__ );
 275
 276                 $handle = $this->getWriter();
 277
 278                 if ( !$handle ) {
 279                         wfProfileOut( __METHOD__ );
 280                         return false;
 281                 }
 282
 283                 list( $value, $expiry ) = $this->decode( dba_fetch( $key, $handle ) );
 284                 if ( $value !== false ) {
 285                         if ( $expiry && $expiry < time() ) {
 286                                 # Key is expired, delete it
 287                                 dba_delete( $key, $handle );
 288                                 wfDebug( __METHOD__ . ": $key expired\n" );
 289                                 $value = false;
 290                         } else {
 291                                 $value += $step;
 292                                 $blob = $this->encode( $value, $expiry );
 293
 294                                 $ret = dba_replace( $key, $blob, $handle );
 295                                 $value = $ret ? $value : false;
 296                         }
 297                 }
 298
 299                 dba_close( $handle );
 300
 301                 wfProfileOut( __METHOD__ );
 302
 303                 return ( $value === false ) ? false : (int)$value;
 304         }
 305 }