includes/filebackend/lockmanager/LockManager.php

   1 <?php
   2 /**
   3  * @defgroup LockManager Lock management
   4  * @ingroup FileBackend
   5  */
   6
   7 /**
   8  * Resource locking handling.
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License as published by
  12  * the Free Software Foundation; either version 2 of the License, or
  13  * (at your option) any later version.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  18  * GNU General Public License for more details.
  19  *
  20  * You should have received a copy of the GNU General Public License along
  21  * with this program; if not, write to the Free Software Foundation, Inc.,
  22  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  23  * http://www.gnu.org/copyleft/gpl.html
  24  *
  25  * @file
  26  * @ingroup LockManager
  27  * @author Aaron Schulz
  28  */
  29
  30 /**
  31  * @brief Class for handling resource locking.
  32  *
  33  * Locks on resource keys can either be shared or exclusive.
  34  *
  35  * Implementations must keep track of what is locked by this proccess
  36  * in-memory and support nested locking calls (using reference counting).
  37  * At least LOCK_UW and LOCK_EX must be implemented. LOCK_SH can be a no-op.
  38  * Locks should either be non-blocking or have low wait timeouts.
  39  *
  40  * Subclasses should avoid throwing exceptions at all costs.
  41  *
  42  * @ingroup LockManager
  43  * @since 1.19
  44  */
  45 abstract class LockManager {
  46         /** @var Array Mapping of lock types to the type actually used */
  47         protected $lockTypeMap = array(
  48                 self::LOCK_SH => self::LOCK_SH,
  49                 self::LOCK_UW => self::LOCK_EX, // subclasses may use self::LOCK_SH
  50                 self::LOCK_EX => self::LOCK_EX
  51         );
  52
  53         /** @var Array Map of (resource path => lock type => count) */
  54         protected $locksHeld = array();
  55
  56         protected $domain; // string; domain (usually wiki ID)
  57         protected $lockTTL; // integer; maximum time locks can be held
  58
  59         /* Lock types; stronger locks have higher values */
  60         const LOCK_SH = 1; // shared lock (for reads)
  61         const LOCK_UW = 2; // shared lock (for reads used to write elsewhere)
  62         const LOCK_EX = 3; // exclusive lock (for writes)
  63
  64         /**
  65          * Construct a new instance from configuration
  66          *
  67          * $config paramaters include:
  68          *   - domain  : Domain (usually wiki ID) that all resources are relative to [optional]
  69          *   - lockTTL : Age (in seconds) at which resource locks should expire.
  70          *               This only applies if locks are not tied to a connection/process.
  71          *
  72          * @param $config Array
  73          */
  74         public function __construct( array $config ) {
  75                 $this->domain = isset( $config['domain'] ) ? $config['domain'] : wfWikiID();
  76                 if ( isset( $config['lockTTL'] ) ) {
  77                         $this->lockTTL = max( 1, $config['lockTTL'] );
  78                 } elseif ( PHP_SAPI === 'cli' ) {
  79                         $this->lockTTL = 2 * 3600;
  80                 } else {
  81                         $met = ini_get( 'max_execution_time' ); // this is 0 in CLI mode
  82                         $this->lockTTL = max( 5 * 60, 2 * (int)$met );
  83                 }
  84         }
  85
  86         /**
  87          * Lock the resources at the given abstract paths
  88          *
  89          * @param array $paths List of resource names
  90          * @param $type integer LockManager::LOCK_* constant
  91          * @param integer $timeout Timeout in seconds (0 means non-blocking) (since 1.21)
  92          * @return Status
  93          */
  94         final public function lock( array $paths, $type = self::LOCK_EX, $timeout = 0 ) {
  95                 wfProfileIn( __METHOD__ );
  96                 $msleep = array( 0, 50, 100, 300, 500 ); // retry backoff times
  97                 $start = microtime( true );
  98                 do {
  99                         $status = $this->doLock( array_unique( $paths ), $this->lockTypeMap[$type] );
 100                         $elapsed = microtime( true ) - $start;
 101                         if ( $status->isOK() || $elapsed >= $timeout || $elapsed < 0 ) {
 102                                 break; // success, timeout, or clock set back
 103                         }
 104                         usleep( 1e3 * ( next( $msleep ) ?: 1000 ) ); // use 1 sec after enough times
 105                         $elapsed = microtime( true ) - $start;
 106                 } while ( $elapsed < $timeout && $elapsed >= 0 );
 107                 wfProfileOut( __METHOD__ );
 108                 return $status;
 109         }
 110
 111         /**
 112          * Unlock the resources at the given abstract paths
 113          *
 114          * @param array $paths List of storage paths
 115          * @param $type integer LockManager::LOCK_* constant
 116          * @return Status
 117          */
 118         final public function unlock( array $paths, $type = self::LOCK_EX ) {
 119                 wfProfileIn( __METHOD__ );
 120                 $status = $this->doUnlock( array_unique( $paths ), $this->lockTypeMap[$type] );
 121                 wfProfileOut( __METHOD__ );
 122                 return $status;
 123         }
 124
 125         /**
 126          * Get the base 36 SHA-1 of a string, padded to 31 digits.
 127          * Before hashing, the path will be prefixed with the domain ID.
 128          * This should be used interally for lock key or file names.
 129          *
 130          * @param $path string
 131          * @return string
 132          */
 133         final protected function sha1Base36Absolute( $path ) {
 134                 return wfBaseConvert( sha1( "{$this->domain}:{$path}" ), 16, 36, 31 );
 135         }
 136
 137         /**
 138          * Get the base 16 SHA-1 of a string, padded to 31 digits.
 139          * Before hashing, the path will be prefixed with the domain ID.
 140          * This should be used interally for lock key or file names.
 141          *
 142          * @param $path string
 143          * @return string
 144          */
 145         final protected function sha1Base16Absolute( $path ) {
 146                 return sha1( "{$this->domain}:{$path}" );
 147         }
 148
 149         /**
 150          * Lock resources with the given keys and lock type
 151          *
 152          * @param array $paths List of storage paths
 153          * @param $type integer LockManager::LOCK_* constant
 154          * @return Status
 155          */
 156         abstract protected function doLock( array $paths, $type );
 157
 158         /**
 159          * Unlock resources with the given keys and lock type
 160          *
 161          * @param array $paths List of storage paths
 162          * @param $type integer LockManager::LOCK_* constant
 163          * @return Status
 164          */
 165         abstract protected function doUnlock( array $paths, $type );
 166 }
 167
 168 /**
 169  * Simple version of LockManager that does nothing
 170  * @since 1.19
 171  */
 172 class NullLockManager extends LockManager {
 173         /**
 174          * @see LockManager::doLock()
 175          * @param $paths array
 176          * @param $type int
 177          * @return Status
 178          */
 179         protected function doLock( array $paths, $type ) {
 180                 return Status::newGood();
 181         }
 182
 183         /**
 184          * @see LockManager::doUnlock()
 185          * @param $paths array
 186          * @param $type int
 187          * @return Status
 188          */
 189         protected function doUnlock( array $paths, $type ) {
 190                 return Status::newGood();
 191         }
 192 }