includes/objectcache/DBABagOStuff.php

   1 <?php
   2
   3 /**
   4  * Cache that uses DBA as a backend.
   5  * Slow due to the need to constantly open and close the file to avoid holding
   6  * writer locks. Intended for development use only,  as a memcached workalike
   7  * for systems that don't have it.
   8  *
   9  * @ingroup Cache
  10  */
  11 class DBABagOStuff extends BagOStuff {
  12         var $mHandler, $mFile, $mReader, $mWriter, $mDisabled;
  13
  14         public function __construct( $dir = false ) {
  15                 global $wgDBAhandler;
  16
  17                 if ( $dir === false ) {
  18                         global $wgTmpDirectory;
  19                         $dir = $wgTmpDirectory;
  20                 }
  21
  22                 $this->mFile = "$dir/mw-cache-" . wfWikiID();
  23                 $this->mFile .= '.db';
  24                 wfDebug( __CLASS__ . ": using cache file {$this->mFile}\n" );
  25                 $this->mHandler = $wgDBAhandler;
  26         }
  27
  28         /**
  29          * Encode value and expiry for storage
  30          */
  31         function encode( $value, $expiry ) {
  32                 # Convert to absolute time
  33                 $expiry = $this->convertExpiry( $expiry );
  34
  35                 return sprintf( '%010u', intval( $expiry ) ) . ' ' . serialize( $value );
  36         }
  37
  38         /**
  39          * @return list containing value first and expiry second
  40          */
  41         function decode( $blob ) {
  42                 if ( !is_string( $blob ) ) {
  43                         return array( null, 0 );
  44                 } else {
  45                         return array(
  46                                 unserialize( substr( $blob, 11 ) ),
  47                                 intval( substr( $blob, 0, 10 ) )
  48                         );
  49                 }
  50         }
  51
  52         function getReader() {
  53                 if ( file_exists( $this->mFile ) ) {
  54                         $handle = dba_open( $this->mFile, 'rl', $this->mHandler );
  55                 } else {
  56                         $handle = $this->getWriter();
  57                 }
  58
  59                 if ( !$handle ) {
  60                         wfDebug( "Unable to open DBA cache file {$this->mFile}\n" );
  61                 }
  62
  63                 return $handle;
  64         }
  65
  66         function getWriter() {
  67                 $handle = dba_open( $this->mFile, 'cl', $this->mHandler );
  68
  69                 if ( !$handle ) {
  70                         wfDebug( "Unable to open DBA cache file {$this->mFile}\n" );
  71                 }
  72
  73                 return $handle;
  74         }
  75
  76         function get( $key ) {
  77                 wfProfileIn( __METHOD__ );
  78                 wfDebug( __METHOD__ . "($key)\n" );
  79
  80                 $handle = $this->getReader();
  81                 if ( !$handle ) {
  82                         wfProfileOut( __METHOD__ );
  83                         return null;
  84                 }
  85
  86                 $val = dba_fetch( $key, $handle );
  87                 list( $val, $expiry ) = $this->decode( $val );
  88
  89                 # Must close ASAP because locks are held
  90                 dba_close( $handle );
  91
  92                 if ( !is_null( $val ) && $expiry && $expiry < time() ) {
  93                         # Key is expired, delete it
  94                         $handle = $this->getWriter();
  95                         dba_delete( $key, $handle );
  96                         dba_close( $handle );
  97                         wfDebug( __METHOD__ . ": $key expired\n" );
  98                         $val = null;
  99                 }
 100
 101                 wfProfileOut( __METHOD__ );
 102                 return $val;
 103         }
 104
 105         function set( $key, $value, $exptime = 0 ) {
 106                 wfProfileIn( __METHOD__ );
 107                 wfDebug( __METHOD__ . "($key)\n" );
 108
 109                 $blob = $this->encode( $value, $exptime );
 110
 111                 $handle = $this->getWriter();
 112                 if ( !$handle ) {
 113                         wfProfileOut( __METHOD__ );
 114                         return false;
 115                 }
 116
 117                 $ret = dba_replace( $key, $blob, $handle );
 118                 dba_close( $handle );
 119
 120                 wfProfileOut( __METHOD__ );
 121                 return $ret;
 122         }
 123
 124         function delete( $key, $time = 0 ) {
 125                 wfProfileIn( __METHOD__ );
 126                 wfDebug( __METHOD__ . "($key)\n" );
 127
 128                 $handle = $this->getWriter();
 129                 if ( !$handle ) {
 130                         wfProfileOut( __METHOD__ );
 131                         return false;
 132                 }
 133
 134                 $ret = dba_delete( $key, $handle );
 135                 dba_close( $handle );
 136
 137                 wfProfileOut( __METHOD__ );
 138                 return $ret;
 139         }
 140
 141         function add( $key, $value, $exptime = 0 ) {
 142                 wfProfileIn( __METHOD__ );
 143
 144                 $blob = $this->encode( $value, $exptime );
 145
 146                 $handle = $this->getWriter();
 147
 148                 if ( !$handle ) {
 149                         wfProfileOut( __METHOD__ );
 150                         return false;
 151                 }
 152
 153                 $ret = dba_insert( $key, $blob, $handle );
 154
 155                 # Insert failed, check to see if it failed due to an expired key
 156                 if ( !$ret ) {
 157                         list( $value, $expiry ) = $this->decode( dba_fetch( $key, $handle ) );
 158
 159                         if ( $expiry < time() ) {
 160                                 # Yes expired, delete and try again
 161                                 dba_delete( $key, $handle );
 162                                 $ret = dba_insert( $key, $blob, $handle );
 163                                 # This time if it failed then it will be handled by the caller like any other race
 164                         }
 165                 }
 166
 167                 dba_close( $handle );
 168
 169                 wfProfileOut( __METHOD__ );
 170                 return $ret;
 171         }
 172
 173         function keys() {
 174                 $reader = $this->getReader();
 175                 $k1 = dba_firstkey( $reader );
 176
 177                 if ( !$k1 ) {
 178                         return array();
 179                 }
 180
 181                 $result[] = $k1;
 182
 183                 while ( $key = dba_nextkey( $reader ) ) {
 184                         $result[] = $key;
 185                 }
 186
 187                 return $result;
 188         }
 189 }
 190