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          * @param array $config Parameters 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         public function __construct( array $config ) {
  73                 $this->domain = isset( $config['domain'] ) ? $config['domain'] : wfWikiID();
  74                 if ( isset( $config['lockTTL'] ) ) {
  75                         $this->lockTTL = max( 5, $config['lockTTL'] );
  76                 } elseif ( PHP_SAPI === 'cli' ) {
  77                         $this->lockTTL = 3600;
  78                 } else {
  79                         $met = ini_get( 'max_execution_time' ); // this is 0 in CLI mode
  80                         $this->lockTTL = max( 5 * 60, 2 * (int)$met );
  81                 }
  82         }
  83
  84         /**
  85          * Lock the resources at the given abstract paths
  86          *
  87          * @param array $paths List of resource names
  88          * @param int $type LockManager::LOCK_* constant
  89          * @param int $timeout Timeout in seconds (0 means non-blocking) (since 1.21)
  90          * @return Status
  91          */
  92         final public function lock( array $paths, $type = self::LOCK_EX, $timeout = 0 ) {
  93                 return $this->lockByType( array( $type => $paths ), $timeout );
  94         }
  95
  96         /**
  97          * Lock the resources at the given abstract paths
  98          *
  99          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 100          * @param int $timeout Timeout in seconds (0 means non-blocking) (since 1.21)
 101          * @return Status
 102          * @since 1.22
 103          */
 104         final public function lockByType( array $pathsByType, $timeout = 0 ) {
 105                 $pathsByType = $this->normalizePathsByType( $pathsByType );
 106                 $msleep = array( 0, 50, 100, 300, 500 ); // retry backoff times
 107                 $start = microtime( true );
 108                 do {
 109                         $status = $this->doLockByType( $pathsByType );
 110                         $elapsed = microtime( true ) - $start;
 111                         if ( $status->isOK() || $elapsed >= $timeout || $elapsed < 0 ) {
 112                                 break; // success, timeout, or clock set back
 113                         }
 114                         usleep( 1e3 * ( next( $msleep ) ?: 1000 ) ); // use 1 sec after enough times
 115                         $elapsed = microtime( true ) - $start;
 116                 } while ( $elapsed < $timeout && $elapsed >= 0 );
 117
 118                 return $status;
 119         }
 120
 121         /**
 122          * Unlock the resources at the given abstract paths
 123          *
 124          * @param array $paths List of paths
 125          * @param int $type LockManager::LOCK_* constant
 126          * @return Status
 127          */
 128         final public function unlock( array $paths, $type = self::LOCK_EX ) {
 129                 return $this->unlockByType( array( $type => $paths ) );
 130         }
 131
 132         /**
 133          * Unlock the resources at the given abstract paths
 134          *
 135          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 136          * @return Status
 137          * @since 1.22
 138          */
 139         final public function unlockByType( array $pathsByType ) {
 140                 $pathsByType = $this->normalizePathsByType( $pathsByType );
 141                 $status = $this->doUnlockByType( $pathsByType );
 142
 143                 return $status;
 144         }
 145
 146         /**
 147          * Get the base 36 SHA-1 of a string, padded to 31 digits.
 148          * Before hashing, the path will be prefixed with the domain ID.
 149          * This should be used interally for lock key or file names.
 150          *
 151          * @param string $path
 152          * @return string
 153          */
 154         final protected function sha1Base36Absolute( $path ) {
 155                 return Wikimedia\base_convert( sha1( "{$this->domain}:{$path}" ), 16, 36, 31 );
 156         }
 157
 158         /**
 159          * Get the base 16 SHA-1 of a string, padded to 31 digits.
 160          * Before hashing, the path will be prefixed with the domain ID.
 161          * This should be used interally for lock key or file names.
 162          *
 163          * @param string $path
 164          * @return string
 165          */
 166         final protected function sha1Base16Absolute( $path ) {
 167                 return sha1( "{$this->domain}:{$path}" );
 168         }
 169
 170         /**
 171          * Normalize the $paths array by converting LOCK_UW locks into the
 172          * appropriate type and removing any duplicated paths for each lock type.
 173          *
 174          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 175          * @return array
 176          * @since 1.22
 177          */
 178         final protected function normalizePathsByType( array $pathsByType ) {
 179                 $res = array();
 180                 foreach ( $pathsByType as $type => $paths ) {
 181                         $res[$this->lockTypeMap[$type]] = array_unique( $paths );
 182                 }
 183
 184                 return $res;
 185         }
 186
 187         /**
 188          * @see LockManager::lockByType()
 189          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 190          * @return Status
 191          * @since 1.22
 192          */
 193         protected function doLockByType( array $pathsByType ) {
 194                 $status = Status::newGood();
 195                 $lockedByType = array(); // map of (type => paths)
 196                 foreach ( $pathsByType as $type => $paths ) {
 197                         $status->merge( $this->doLock( $paths, $type ) );
 198                         if ( $status->isOK() ) {
 199                                 $lockedByType[$type] = $paths;
 200                         } else {
 201                                 // Release the subset of locks that were acquired
 202                                 foreach ( $lockedByType as $lType => $lPaths ) {
 203                                         $status->merge( $this->doUnlock( $lPaths, $lType ) );
 204                                 }
 205                                 break;
 206                         }
 207                 }
 208
 209                 return $status;
 210         }
 211
 212         /**
 213          * Lock resources with the given keys and lock type
 214          *
 215          * @param array $paths List of paths
 216          * @param int $type LockManager::LOCK_* constant
 217          * @return Status
 218          */
 219         abstract protected function doLock( array $paths, $type );
 220
 221         /**
 222          * @see LockManager::unlockByType()
 223          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 224          * @return Status
 225          * @since 1.22
 226          */
 227         protected function doUnlockByType( array $pathsByType ) {
 228                 $status = Status::newGood();
 229                 foreach ( $pathsByType as $type => $paths ) {
 230                         $status->merge( $this->doUnlock( $paths, $type ) );
 231                 }
 232
 233                 return $status;
 234         }
 235
 236         /**
 237          * Unlock resources with the given keys and lock type
 238          *
 239          * @param array $paths List of paths
 240          * @param int $type LockManager::LOCK_* constant
 241          * @return Status
 242          */
 243         abstract protected function doUnlock( array $paths, $type );
 244 }
 245
 246 /**
 247  * Simple version of LockManager that does nothing
 248  * @since 1.19
 249  */
 250 class NullLockManager extends LockManager {
 251         protected function doLock( array $paths, $type ) {
 252                 return Status::newGood();
 253         }
 254
 255         protected function doUnlock( array $paths, $type ) {
 256                 return Status::newGood();
 257         }
 258 }