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                 $status = Status::newGood();
 106                 $pathsByType = $this->normalizePathsByType( $pathsByType );
 107                 $msleep = array( 0, 50, 100, 300, 500 ); // retry backoff times
 108                 $start = microtime( true );
 109                 do {
 110                         $status = $this->doLockByType( $pathsByType );
 111                         $elapsed = microtime( true ) - $start;
 112                         if ( $status->isOK() || $elapsed >= $timeout || $elapsed < 0 ) {
 113                                 break; // success, timeout, or clock set back
 114                         }
 115                         usleep( 1e3 * ( next( $msleep ) ?: 1000 ) ); // use 1 sec after enough times
 116                         $elapsed = microtime( true ) - $start;
 117                 } while ( $elapsed < $timeout && $elapsed >= 0 );
 118
 119                 return $status;
 120         }
 121
 122         /**
 123          * Unlock the resources at the given abstract paths
 124          *
 125          * @param array $paths List of paths
 126          * @param int $type LockManager::LOCK_* constant
 127          * @return Status
 128          */
 129         final public function unlock( array $paths, $type = self::LOCK_EX ) {
 130                 return $this->unlockByType( array( $type => $paths ) );
 131         }
 132
 133         /**
 134          * Unlock the resources at the given abstract paths
 135          *
 136          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 137          * @return Status
 138          * @since 1.22
 139          */
 140         final public function unlockByType( array $pathsByType ) {
 141                 $pathsByType = $this->normalizePathsByType( $pathsByType );
 142                 $status = $this->doUnlockByType( $pathsByType );
 143
 144                 return $status;
 145         }
 146
 147         /**
 148          * Get the base 36 SHA-1 of a string, padded to 31 digits.
 149          * Before hashing, the path will be prefixed with the domain ID.
 150          * This should be used interally for lock key or file names.
 151          *
 152          * @param string $path
 153          * @return string
 154          */
 155         final protected function sha1Base36Absolute( $path ) {
 156                 return wfBaseConvert( sha1( "{$this->domain}:{$path}" ), 16, 36, 31 );
 157         }
 158
 159         /**
 160          * Get the base 16 SHA-1 of a string, padded to 31 digits.
 161          * Before hashing, the path will be prefixed with the domain ID.
 162          * This should be used interally for lock key or file names.
 163          *
 164          * @param string $path
 165          * @return string
 166          */
 167         final protected function sha1Base16Absolute( $path ) {
 168                 return sha1( "{$this->domain}:{$path}" );
 169         }
 170
 171         /**
 172          * Normalize the $paths array by converting LOCK_UW locks into the
 173          * appropriate type and removing any duplicated paths for each lock type.
 174          *
 175          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 176          * @return array
 177          * @since 1.22
 178          */
 179         final protected function normalizePathsByType( array $pathsByType ) {
 180                 $res = array();
 181                 foreach ( $pathsByType as $type => $paths ) {
 182                         $res[$this->lockTypeMap[$type]] = array_unique( $paths );
 183                 }
 184
 185                 return $res;
 186         }
 187
 188         /**
 189          * @see LockManager::lockByType()
 190          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 191          * @return Status
 192          * @since 1.22
 193          */
 194         protected function doLockByType( array $pathsByType ) {
 195                 $status = Status::newGood();
 196                 $lockedByType = array(); // map of (type => paths)
 197                 foreach ( $pathsByType as $type => $paths ) {
 198                         $status->merge( $this->doLock( $paths, $type ) );
 199                         if ( $status->isOK() ) {
 200                                 $lockedByType[$type] = $paths;
 201                         } else {
 202                                 // Release the subset of locks that were acquired
 203                                 foreach ( $lockedByType as $lType => $lPaths ) {
 204                                         $status->merge( $this->doUnlock( $lPaths, $lType ) );
 205                                 }
 206                                 break;
 207                         }
 208                 }
 209
 210                 return $status;
 211         }
 212
 213         /**
 214          * Lock resources with the given keys and lock type
 215          *
 216          * @param array $paths List of paths
 217          * @param int $type LockManager::LOCK_* constant
 218          * @return Status
 219          */
 220         abstract protected function doLock( array $paths, $type );
 221
 222         /**
 223          * @see LockManager::unlockByType()
 224          * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
 225          * @return Status
 226          * @since 1.22
 227          */
 228         protected function doUnlockByType( array $pathsByType ) {
 229                 $status = Status::newGood();
 230                 foreach ( $pathsByType as $type => $paths ) {
 231                         $status->merge( $this->doUnlock( $paths, $type ) );
 232                 }
 233
 234                 return $status;
 235         }
 236
 237         /**
 238          * Unlock resources with the given keys and lock type
 239          *
 240          * @param array $paths List of paths
 241          * @param int $type LockManager::LOCK_* constant
 242          * @return Status
 243          */
 244         abstract protected function doUnlock( array $paths, $type );
 245 }
 246
 247 /**
 248  * Simple version of LockManager that does nothing
 249  * @since 1.19
 250  */
 251 class NullLockManager extends LockManager {
 252         protected function doLock( array $paths, $type ) {
 253                 return Status::newGood();
 254         }
 255
 256         protected function doUnlock( array $paths, $type ) {
 257                 return Status::newGood();
 258         }
 259 }