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+<?php
+/**
+ * @defgroup LockManager Lock management
+ * @ingroup FileBackend
+ */
+use Psr\Log\LoggerInterface;
+use Wikimedia\WaitConditionLoop;
+
+/**
+ * Resource locking handling.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ * @ingroup LockManager
+ */
+
+/**
+ * @brief Class for handling resource locking.
+ *
+ * Locks on resource keys can either be shared or exclusive.
+ *
+ * Implementations must keep track of what is locked by this process
+ * in-memory and support nested locking calls (using reference counting).
+ * At least LOCK_UW and LOCK_EX must be implemented. LOCK_SH can be a no-op.
+ * Locks should either be non-blocking or have low wait timeouts.
+ *
+ * Subclasses should avoid throwing exceptions at all costs.
+ *
+ * @ingroup LockManager
+ * @since 1.19
+ */
+abstract class LockManager {
+	/** @var LoggerInterface */
+	protected $logger;
+
+	/** @var array Mapping of lock types to the type actually used */
+	protected $lockTypeMap = [
+		self::LOCK_SH => self::LOCK_SH,
+		self::LOCK_UW => self::LOCK_EX, // subclasses may use self::LOCK_SH
+		self::LOCK_EX => self::LOCK_EX
+	];
+
+	/** @var array Map of (resource path => lock type => count) */
+	protected $locksHeld = [];
+
+	protected $domain; // string; domain (usually wiki ID)
+	protected $lockTTL; // integer; maximum time locks can be held
+
+	/** @var string Random 32-char hex number */
+	protected $session;
+
+	/** Lock types; stronger locks have higher values */
+	const LOCK_SH = 1; // shared lock (for reads)
+	const LOCK_UW = 2; // shared lock (for reads used to write elsewhere)
+	const LOCK_EX = 3; // exclusive lock (for writes)
+
+	/** @var int Max expected lock expiry in any context */
+	const MAX_LOCK_TTL = 7200; // 2 hours
+
+	/**
+	 * Construct a new instance from configuration
+	 *
+	 * @param array $config Parameters include:
+	 *   - domain  : Domain (usually wiki ID) that all resources are relative to [optional]
+	 *   - lockTTL : Age (in seconds) at which resource locks should expire.
+	 *               This only applies if locks are not tied to a connection/process.
+	 */
+	public function __construct( array $config ) {
+		$this->domain = isset( $config['domain'] ) ? $config['domain'] : 'global';
+		if ( isset( $config['lockTTL'] ) ) {
+			$this->lockTTL = max( 5, $config['lockTTL'] );
+		} elseif ( PHP_SAPI === 'cli' ) {
+			$this->lockTTL = 3600;
+		} else {
+			$met = ini_get( 'max_execution_time' ); // this is 0 in CLI mode
+			$this->lockTTL = max( 5 * 60, 2 * (int)$met );
+		}
+
+		// Upper bound on how long to keep lock structures around. This is useful when setting
+		// TTLs, as the "lockTTL" value may vary based on CLI mode and app server group. This is
+		// a "safe" value that can be used to avoid clobbering other locks that use high TTLs.
+		$this->lockTTL = min( $this->lockTTL, self::MAX_LOCK_TTL );
+
+		$random = [];
+		for ( $i = 1; $i <= 5; ++$i ) {
+			$random[] = mt_rand( 0, 0xFFFFFFF );
+		}
+		$this->session = md5( implode( '-', $random ) );
+
+		$this->logger = isset( $config['logger'] ) ? $config['logger'] : new \Psr\Log\NullLogger();
+	}
+
+	/**
+	 * Lock the resources at the given abstract paths
+	 *
+	 * @param array $paths List of resource names
+	 * @param int $type LockManager::LOCK_* constant
+	 * @param int $timeout Timeout in seconds (0 means non-blocking) (since 1.21)
+	 * @return StatusValue
+	 */
+	final public function lock( array $paths, $type = self::LOCK_EX, $timeout = 0 ) {
+		return $this->lockByType( [ $type => $paths ], $timeout );
+	}
+
+	/**
+	 * Lock the resources at the given abstract paths
+	 *
+	 * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+	 * @param int $timeout Timeout in seconds (0 means non-blocking) (since 1.21)
+	 * @return StatusValue
+	 * @since 1.22
+	 */
+	final public function lockByType( array $pathsByType, $timeout = 0 ) {
+		$pathsByType = $this->normalizePathsByType( $pathsByType );
+
+		$status = null;
+		$loop = new WaitConditionLoop(
+			function () use ( &$status, $pathsByType ) {
+				$status = $this->doLockByType( $pathsByType );
+
+				return $status->isOK() ?: WaitConditionLoop::CONDITION_CONTINUE;
+			},
+			$timeout
+		);
+		$loop->invoke();
+
+		return $status;
+	}
+
+	/**
+	 * Unlock the resources at the given abstract paths
+	 *
+	 * @param array $paths List of paths
+	 * @param int $type LockManager::LOCK_* constant
+	 * @return StatusValue
+	 */
+	final public function unlock( array $paths, $type = self::LOCK_EX ) {
+		return $this->unlockByType( [ $type => $paths ] );
+	}
+
+	/**
+	 * Unlock the resources at the given abstract paths
+	 *
+	 * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+	 * @return StatusValue
+	 * @since 1.22
+	 */
+	final public function unlockByType( array $pathsByType ) {
+		$pathsByType = $this->normalizePathsByType( $pathsByType );
+		$status = $this->doUnlockByType( $pathsByType );
+
+		return $status;
+	}
+
+	/**
+	 * Get the base 36 SHA-1 of a string, padded to 31 digits.
+	 * Before hashing, the path will be prefixed with the domain ID.
+	 * This should be used internally for lock key or file names.
+	 *
+	 * @param string $path
+	 * @return string
+	 */
+	final protected function sha1Base36Absolute( $path ) {
+		return Wikimedia\base_convert( sha1( "{$this->domain}:{$path}" ), 16, 36, 31 );
+	}
+
+	/**
+	 * Get the base 16 SHA-1 of a string, padded to 31 digits.
+	 * Before hashing, the path will be prefixed with the domain ID.
+	 * This should be used internally for lock key or file names.
+	 *
+	 * @param string $path
+	 * @return string
+	 */
+	final protected function sha1Base16Absolute( $path ) {
+		return sha1( "{$this->domain}:{$path}" );
+	}
+
+	/**
+	 * Normalize the $paths array by converting LOCK_UW locks into the
+	 * appropriate type and removing any duplicated paths for each lock type.
+	 *
+	 * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+	 * @return array
+	 * @since 1.22
+	 */
+	final protected function normalizePathsByType( array $pathsByType ) {
+		$res = [];
+		foreach ( $pathsByType as $type => $paths ) {
+			$res[$this->lockTypeMap[$type]] = array_unique( $paths );
+		}
+
+		return $res;
+	}
+
+	/**
+	 * @see LockManager::lockByType()
+	 * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+	 * @return StatusValue
+	 * @since 1.22
+	 */
+	protected function doLockByType( array $pathsByType ) {
+		$status = StatusValue::newGood();
+		$lockedByType = []; // map of (type => paths)
+		foreach ( $pathsByType as $type => $paths ) {
+			$status->merge( $this->doLock( $paths, $type ) );
+			if ( $status->isOK() ) {
+				$lockedByType[$type] = $paths;
+			} else {
+				// Release the subset of locks that were acquired
+				foreach ( $lockedByType as $lType => $lPaths ) {
+					$status->merge( $this->doUnlock( $lPaths, $lType ) );
+				}
+				break;
+			}
+		}
+
+		return $status;
+	}
+
+	/**
+	 * Lock resources with the given keys and lock type
+	 *
+	 * @param array $paths List of paths
+	 * @param int $type LockManager::LOCK_* constant
+	 * @return StatusValue
+	 */
+	abstract protected function doLock( array $paths, $type );
+
+	/**
+	 * @see LockManager::unlockByType()
+	 * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+	 * @return StatusValue
+	 * @since 1.22
+	 */
+	protected function doUnlockByType( array $pathsByType ) {
+		$status = StatusValue::newGood();
+		foreach ( $pathsByType as $type => $paths ) {
+			$status->merge( $this->doUnlock( $paths, $type ) );
+		}
+
+		return $status;
+	}
+
+	/**
+	 * Unlock resources with the given keys and lock type
+	 *
+	 * @param array $paths List of paths
+	 * @param int $type LockManager::LOCK_* constant
+	 * @return StatusValue
+	 */
+	abstract protected function doUnlock( array $paths, $type );
+}