1 files changed, 153 insertions, 48 deletions

diff --git a/includes/libs/objectcache/BagOStuff.php b/includes/libs/objectcache/BagOStuff.php
index 0b791e5a..ddbe8eaa 100644
--- a/includes/libs/objectcache/BagOStuff.php
+++ b/includes/libs/objectcache/BagOStuff.php
@@ -1,7 +1,5 @@
 <?php
 /**
- * Classes to cache objects in PHP accelerators, SQL database or DBA files
- *
  * Copyright © 2003-2004 Brion Vibber <brion@pobox.com>
  * https://www.mediawiki.org/
  *
@@ -37,29 +35,34 @@ use Psr\Log\NullLogger;
  * the PHP memcached client.
  *
  * backends for local hash array and SQL table included:
- * <code>
+ * @code
  *   $bag = new HashBagOStuff();
  *   $bag = new SqlBagOStuff(); # connect to db first
- * </code>
+ * @endcode
  *
  * @ingroup Cache
  */
 abstract class BagOStuff implements LoggerAwareInterface {
-	private $debugMode = false;
-
+	/** @var array[] Lock tracking */
+	protected $locks = array();
+	/** @var integer */
 	protected $lastError = self::ERR_NONE;
 
-	/**
-	 * @var LoggerInterface
-	 */
+	/** @var LoggerInterface */
 	protected $logger;
 
+	/** @var bool */
+	private $debugMode = false;
+
 	/** Possible values for getLastError() */
 	const ERR_NONE = 0; // no error
 	const ERR_NO_RESPONSE = 1; // no response
 	const ERR_UNREACHABLE = 2; // can't connect
 	const ERR_UNEXPECTED = 3; // response gave some error
 
+	/** Bitfield constants for get()/getMulti() */
+	const READ_LATEST = 1; // use latest data for replicated stores
+
 	public function __construct( array $params = array() ) {
 		if ( isset( $params['logger'] ) ) {
 			$this->setLogger( $params['logger'] );
@@ -87,9 +90,10 @@ abstract class BagOStuff implements LoggerAwareInterface {
 	 * Get an item with the given key. Returns false if it does not exist.
 	 * @param string $key
 	 * @param mixed $casToken [optional]
+	 * @param integer $flags Bitfield; supports READ_LATEST [optional]
 	 * @return mixed Returns false on failure
 	 */
-	abstract public function get( $key, &$casToken = null );
+	abstract public function get( $key, &$casToken = null, $flags = 0 );
 
 	/**
 	 * Set an item.
@@ -109,18 +113,20 @@ abstract class BagOStuff implements LoggerAwareInterface {
 
 	/**
 	 * Merge changes into the existing cache value (possibly creating a new one).
-	 * The callback function returns the new value given the current value (possibly false),
-	 * and takes the arguments: (this BagOStuff object, cache key, current value).
+	 * The callback function returns the new value given the current value
+	 * (which will be false if not present), and takes the arguments:
+	 * (this BagOStuff, cache key, current value).
 	 *
 	 * @param string $key
 	 * @param callable $callback Callback method to be executed
 	 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 	 * @param int $attempts The amount of times to attempt a merge in case of failure
 	 * @return bool Success
+	 * @throws InvalidArgumentException
 	 */
 	public function merge( $key, $callback, $exptime = 0, $attempts = 10 ) {
 		if ( !is_callable( $callback ) ) {
-			throw new Exception( "Got invalid callback." );
+			throw new InvalidArgumentException( "Got invalid callback." );
 		}
 
 		return $this->mergeViaLock( $key, $callback, $exptime, $attempts );
@@ -137,11 +143,17 @@ abstract class BagOStuff implements LoggerAwareInterface {
 	 */
 	protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 		do {
+			$this->clearLastError();
 			$casToken = null; // passed by reference
 			$currentValue = $this->get( $key, $casToken );
+			if ( $this->getLastError() ) {
+				return false; // don't spam retries (retry only on races)
+			}
+
 			// Derive the new value from the old value
 			$value = call_user_func( $callback, $this, $key, $currentValue );
 
+			$this->clearLastError();
 			if ( $value === false ) {
 				$success = true; // do nothing
 			} elseif ( $currentValue === false ) {
@@ -151,6 +163,9 @@ abstract class BagOStuff implements LoggerAwareInterface {
 				// Try to update the key, failing if it gets changed in the meantime
 				$success = $this->cas( $casToken, $key, $value, $exptime );
 			}
+			if ( $this->getLastError() ) {
+				return false; // IO error; don't spam retries
+			}
 		} while ( !$success && --$attempts );
 
 		return $success;
@@ -164,6 +179,7 @@ abstract class BagOStuff implements LoggerAwareInterface {
 	 * @param mixed $value
 	 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 	 * @return bool Success
+	 * @throws Exception
 	 */
 	protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 		throw new Exception( "CAS is not implemented in " . __CLASS__ );
@@ -183,14 +199,18 @@ abstract class BagOStuff implements LoggerAwareInterface {
 			return false;
 		}
 
+		$this->clearLastError();
 		$currentValue = $this->get( $key );
-		// Derive the new value from the old value
-		$value = call_user_func( $callback, $this, $key, $currentValue );
-
-		if ( $value === false ) {
-			$success = true; // do nothing
+		if ( $this->getLastError() ) {
+			$success = false;
 		} else {
-			$success = $this->set( $key, $value, $exptime ); // set the new value
+			// Derive the new value from the old value
+			$value = call_user_func( $callback, $this, $key, $currentValue );
+			if ( $value === false ) {
+				$success = true; // do nothing
+			} else {
+				$success = $this->set( $key, $value, $exptime ); // set the new value
+			}
 		}
 
 		if ( !$this->unlock( $key ) ) {
@@ -202,48 +222,116 @@ abstract class BagOStuff implements LoggerAwareInterface {
 	}
 
 	/**
+	 * Acquire an advisory lock on a key string
+	 *
+	 * Note that if reentry is enabled, duplicate calls ignore $expiry
+	 *
 	 * @param string $key
-	 * @param int $timeout Lock wait timeout [optional]
-	 * @param int $expiry Lock expiry [optional]
+	 * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
+	 * @param int $expiry Lock expiry [optional]; 1 day maximum
+	 * @param string $rclass Allow reentry if set and the current lock used this value
 	 * @return bool Success
 	 */
-	public function lock( $key, $timeout = 6, $expiry = 6 ) {
+	public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
+		// Avoid deadlocks and allow lock reentry if specified
+		if ( isset( $this->locks[$key] ) ) {
+			if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
+				++$this->locks[$key]['depth'];
+				return true;
+			} else {
+				return false;
+			}
+		}
+
+		$expiry = min( $expiry ?: INF, 86400 );
+
 		$this->clearLastError();
 		$timestamp = microtime( true ); // starting UNIX timestamp
 		if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
-			return true;
-		} elseif ( $this->getLastError() ) {
-			return false;
+			$locked = true;
+		} elseif ( $this->getLastError() || $timeout <= 0 ) {
+			$locked = false; // network partition or non-blocking
+		} else {
+			$uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
+			$sleep = 2 * $uRTT; // rough time to do get()+set()
+
+			$attempts = 0; // failed attempts
+			do {
+				if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
+					// Exponentially back off after failed attempts to avoid network spam.
+					// About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
+					$sleep *= 2;
+				}
+				usleep( $sleep ); // back off
+				$this->clearLastError();
+				$locked = $this->add( "{$key}:lock", 1, $expiry );
+				if ( $this->getLastError() ) {
+					$locked = false; // network partition
+					break;
+				}
+			} while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
 		}
 
-		$uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
-		$sleep = 2 * $uRTT; // rough time to do get()+set()
-
-		$locked = false; // lock acquired
-		$attempts = 0; // failed attempts
-		do {
-			if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
-				// Exponentially back off after failed attempts to avoid network spam.
-				// About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
-				$sleep *= 2;
-			}
-			usleep( $sleep ); // back off
-			$this->clearLastError();
-			$locked = $this->add( "{$key}:lock", 1, $expiry );
-			if ( $this->getLastError() ) {
-				return false;
-			}
-		} while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
+		if ( $locked ) {
+			$this->locks[$key] = array( 'class' => $rclass, 'depth' => 1 );
+		}
 
 		return $locked;
 	}
 
 	/**
+	 * Release an advisory lock on a key string
+	 *
 	 * @param string $key
 	 * @return bool Success
 	 */
 	public function unlock( $key ) {
-		return $this->delete( "{$key}:lock" );
+		if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
+			unset( $this->locks[$key] );
+
+			return $this->delete( "{$key}:lock" );
+		}
+
+		return true;
+	}
+
+	/**
+	 * Get a lightweight exclusive self-unlocking lock
+	 *
+	 * Note that the same lock cannot be acquired twice.
+	 *
+	 * This is useful for task de-duplication or to avoid obtrusive
+	 * (though non-corrupting) DB errors like INSERT key conflicts
+	 * or deadlocks when using LOCK IN SHARE MODE.
+	 *
+	 * @param string $key
+	 * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
+	 * @param int $expiry Lock expiry [optional]; 1 day maximum
+	 * @param string $rclass Allow reentry if set and the current lock used this value
+	 * @return ScopedCallback|null Returns null on failure
+	 * @since 1.26
+	 */
+	final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
+		$expiry = min( $expiry ?: INF, 86400 );
+
+		if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
+			return null;
+		}
+
+		$lSince = microtime( true ); // lock timestamp
+		// PHP 5.3: Can't use $this in a closure
+		$that = $this;
+		$logger = $this->logger;
+
+		return new ScopedCallback( function() use ( $that, $logger, $key, $lSince, $expiry ) {
+			$latency = .050; // latency skew (err towards keeping lock present)
+			$age = ( microtime( true ) - $lSince + $latency );
+			if ( ( $age + $latency ) >= $expiry ) {
+				$logger->warning( "Lock for $key held too long ($age sec)." );
+				return; // expired; it's not "safe" to delete the key
+			}
+			$that->unlock( $key );
+		} );
 	}
 
 	/**
@@ -260,14 +348,13 @@ abstract class BagOStuff implements LoggerAwareInterface {
 		return false;
 	}
 
-	/* *** Emulated functions *** */
-
 	/**
 	 * Get an associative array containing the item for each of the keys that have items.
 	 * @param array $keys List of strings
+	 * @param integer $flags Bitfield; supports READ_LATEST [optional]
 	 * @return array
 	 */
-	public function getMulti( array $keys ) {
+	public function getMulti( array $keys, $flags = 0 ) {
 		$res = array();
 		foreach ( $keys as $key ) {
 			$val = $this->get( $key );
@@ -334,7 +421,7 @@ abstract class BagOStuff implements LoggerAwareInterface {
 	 * Decrease stored value of $key by $value while preserving its TTL
 	 * @param string $key
 	 * @param int $value
-	 * @return int
+	 * @return int|bool New value or false on failure
 	 */
 	public function decr( $key, $value = 1 ) {
 		return $this->incr( $key, - $value );
@@ -384,6 +471,24 @@ abstract class BagOStuff implements LoggerAwareInterface {
 	}
 
 	/**
+	 * Modify a cache update operation array for EventRelayer::notify()
+	 *
+	 * This is used for relayed writes, e.g. for broadcasting a change
+	 * to multiple data-centers. If the array contains a 'val' field
+	 * then the command involves setting a key to that value. Note that
+	 * for simplicity, 'val' is always a simple scalar value. This method
+	 * is used to possibly serialize the value and add any cache-specific
+	 * key/values needed for the relayer daemon (e.g. memcached flags).
+	 *
+	 * @param array $event
+	 * @return array
+	 * @since 1.26
+	 */
+	public function modifySimpleRelayEvent( array $event ) {
+		return $event;
+	}
+
+	/**
 	 * @param string $text
 	 */
 	protected function debug( $text ) {