Update to MediaWiki 1.24.1

5 files changed, 1050 insertions, 0 deletions

diff --git a/includes/poolcounter/PoolCounter.php b/includes/poolcounter/PoolCounter.php
new file mode 100644
index 00000000..e77ffd7c
--- /dev/null
+++ b/includes/poolcounter/PoolCounter.php
@@ -0,0 +1,173 @@
+<?php
+/**
+ * Provides of semaphore semantics for restricting the number
+ * of workers that may be concurrently performing the same task.
+ *
+ * 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
+ */
+
+/**
+ * When you have many workers (threads/servers) giving service, and a
+ * cached item expensive to produce expires, you may get several workers
+ * doing the job at the same time.
+ *
+ * Given enough requests and the item expiring fast (non-cacheable,
+ * lots of edits...) that single work can end up unfairly using most (all)
+ * of the cpu of the pool. This is also known as 'Michael Jackson effect'
+ * since this effect triggered on the english wikipedia on the day Michael
+ * Jackson died, the biographical article got hit with several edits per
+ * minutes and hundreds of read hits.
+ *
+ * The PoolCounter provides semaphore semantics for restricting the number
+ * of workers that may be concurrently performing such single task.
+ *
+ * By default PoolCounter_Stub is used, which provides no locking. You
+ * can get a useful one in the PoolCounter extension.
+ */
+abstract class PoolCounter {
+	/* Return codes */
+	const LOCKED = 1; /* Lock acquired */
+	const RELEASED = 2; /* Lock released */
+	const DONE = 3; /* Another worker did the work for you */
+
+	const ERROR = -1; /* Indeterminate error */
+	const NOT_LOCKED = -2; /* Called release() with no lock held */
+	const QUEUE_FULL = -3; /* There are already maxqueue workers on this lock */
+	const TIMEOUT = -4; /* Timeout exceeded */
+	const LOCK_HELD = -5; /* Cannot acquire another lock while you have one lock held */
+
+	/** @var string All workers with the same key share the lock */
+	protected $key;
+	/** @var int Maximum number of workers working on tasks with the same key simultaneously */
+	protected $workers;
+	/**
+	 * Maximum number of workers working on this task type, regardless of key.
+	 * 0 means unlimited. Max allowed value is 65536.
+	 * The way the slot limit is enforced is overzealous - this option should be used with caution.
+	 * @var int
+	 */
+	protected $slots = 0;
+	/** @var int If this number of workers are already working/waiting, fail instead of wait */
+	protected $maxqueue;
+	/** @var float Maximum time in seconds to wait for the lock */
+	protected $timeout;
+
+	/**
+	 * @param array $conf
+	 * @param string $type
+	 * @param string $key
+	 */
+	protected function __construct( $conf, $type, $key ) {
+		$this->workers = $conf['workers'];
+		$this->maxqueue = $conf['maxqueue'];
+		$this->timeout = $conf['timeout'];
+		if ( isset( $conf['slots'] ) ) {
+			$this->slots = $conf['slots'];
+		}
+
+		if ( $this->slots ) {
+			$key = $this->hashKeyIntoSlots( $key, $this->slots );
+		}
+		$this->key = $key;
+	}
+
+	/**
+	 * Create a Pool counter. This should only be called from the PoolWorks.
+	 *
+	 * @param string $type
+	 * @param string $key
+	 *
+	 * @return PoolCounter
+	 */
+	public static function factory( $type, $key ) {
+		global $wgPoolCounterConf;
+		if ( !isset( $wgPoolCounterConf[$type] ) ) {
+			return new PoolCounter_Stub;
+		}
+		$conf = $wgPoolCounterConf[$type];
+		$class = $conf['class'];
+
+		return new $class( $conf, $type, $key );
+	}
+
+	/**
+	 * @return string
+	 */
+	public function getKey() {
+		return $this->key;
+	}
+
+	/**
+	 * I want to do this task and I need to do it myself.
+	 *
+	 * @return Status Value is one of Locked/Error
+	 */
+	abstract public function acquireForMe();
+
+	/**
+	 * I want to do this task, but if anyone else does it
+	 * instead, it's also fine for me. I will read its cached data.
+	 *
+	 * @return Status Value is one of Locked/Done/Error
+	 */
+	abstract public function acquireForAnyone();
+
+	/**
+	 * I have successfully finished my task.
+	 * Lets another one grab the lock, and returns the workers
+	 * waiting on acquireForAnyone()
+	 *
+	 * @return Status Value is one of Released/NotLocked/Error
+	 */
+	abstract public function release();
+
+	/**
+	 * Given a key (any string) and the number of lots, returns a slot number (an integer from the [0..($slots-1)] range).
+	 * This is used for a global limit on the number of instances  of a given type that can acquire a lock.
+	 * The hashing is deterministic so that PoolCounter::$workers is always an upper limit of how many instances with
+	 * the same key can acquire a lock.
+	 *
+	 * @param string $key PoolCounter instance key (any string)
+	 * @param int $slots The number of slots (max allowed value is 65536)
+	 * @return int
+	 */
+	protected function hashKeyIntoSlots( $key, $slots ) {
+		return hexdec( substr( sha1( $key ), 0, 4 ) ) % $slots;
+	}
+}
+
+// @codingStandardsIgnoreStart Squiz.Classes.ValidClassName.NotCamelCaps
+class PoolCounter_Stub extends PoolCounter {
+	// @codingStandardsIgnoreEnd
+
+	public function __construct() {
+		/* No parameters needed */
+	}
+
+	public function acquireForMe() {
+		return Status::newGood( PoolCounter::LOCKED );
+	}
+
+	public function acquireForAnyone() {
+		return Status::newGood( PoolCounter::LOCKED );
+	}
+
+	public function release() {
+		return Status::newGood( PoolCounter::RELEASED );
+	}
+}
diff --git a/includes/poolcounter/PoolCounterRedis.php b/includes/poolcounter/PoolCounterRedis.php
new file mode 100644
index 00000000..d609f614
--- /dev/null
+++ b/includes/poolcounter/PoolCounterRedis.php
@@ -0,0 +1,417 @@
+<?php
+/**
+ * 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
+ * @author Aaron Schulz
+ */
+
+/**
+ * Version of PoolCounter that uses Redis
+ *
+ * There are four main redis keys used to track each pool counter key:
+ *   - poolcounter:l-slots-*     : A list of available slot IDs for a pool.
+ *   - poolcounter:z-renewtime-* : A sorted set of (slot ID, UNIX timestamp as score)
+ *                                 used for tracking the next time a slot should be
+ *                                 released. This is -1 when a slot is created, and is
+ *                                 set when released (expired), locked, and unlocked.
+ *   - poolcounter:z-wait-*      : A sorted set of (slot ID, UNIX timestamp as score)
+ *                                 used for tracking waiting processes (and wait time).
+ *   - poolcounter:l-wakeup-*    : A list pushed to for the sake of waking up processes
+ *                                 when a any process in the pool finishes (lasts for 1ms).
+ * For a given pool key, all the redis keys start off non-existing and are deleted if not
+ * used for a while to prevent garbage from building up on the server. They are atomically
+ * re-initialized as needed. The "z-renewtime" key is used for detecting sessions which got
+ * slots but then disappeared. Stale entries from there have their timestamp updated and the
+ * corresponding slots freed up. The "z-wait" key is used for detecting processes registered
+ * as waiting but that disappeared. Stale entries from there are deleted and the corresponding
+ * slots are freed up. The worker count is included in all the redis key names as it does not
+ * vary within each $wgPoolCounterConf type and doing so handles configuration changes.
+ *
+ * This class requires Redis 2.6 as it makes use Lua scripts for fast atomic operations.
+ * Also this should be on a server plenty of RAM for the working set to avoid evictions.
+ * Evictions could temporarily allow wait queues to double in size or temporarily cause
+ * pools to appear as full when they are not. Using volatile-ttl and bumping memory-samples
+ * in redis.conf can be helpful otherwise.
+ *
+ * @ingroup Redis
+ * @since 1.23
+ */
+class PoolCounterRedis extends PoolCounter {
+	/** @var HashRing */
+	protected $ring;
+	/** @var RedisConnectionPool */
+	protected $pool;
+	/** @var array (server label => host) map */
+	protected $serversByLabel;
+	/** @var string SHA-1 of the key */
+	protected $keySha1;
+	/** @var int TTL for locks to expire (work should finish in this time) */
+	protected $lockTTL;
+
+	/** @var RedisConnRef */
+	protected $conn;
+	/** @var string Pool slot value */
+	protected $slot;
+	/** @var int AWAKE_* constant */
+	protected $onRelease;
+	/** @var string Unique string to identify this process */
+	protected $session;
+	/** @var int UNIX timestamp */
+	protected $slotTime;
+
+	const AWAKE_ONE = 1; // wake-up if when a slot can be taken from an existing process
+	const AWAKE_ALL = 2; // wake-up if an existing process finishes and wake up such others
+
+	/** @var array List of active PoolCounterRedis objects in this script */
+	protected static $active = null;
+
+	function __construct( $conf, $type, $key ) {
+		parent::__construct( $conf, $type, $key );
+
+		$this->serversByLabel = $conf['servers'];
+		$this->ring = new HashRing( array_fill_keys( array_keys( $conf['servers'] ), 100 ) );
+
+		$conf['redisConfig']['serializer'] = 'none'; // for use with Lua
+		$this->pool = RedisConnectionPool::singleton( $conf['redisConfig'] );
+
+		$this->keySha1 = sha1( $this->key );
+		$met = ini_get( 'max_execution_time' ); // usually 0 in CLI mode
+		$this->lockTTL = $met ? 2 * $met : 3600;
+
+		if ( self::$active === null ) {
+			self::$active = array();
+			register_shutdown_function( array( __CLASS__, 'releaseAll' ) );
+		}
+	}
+
+	/**
+	 * @return Status Uses RediConnRef as value on success
+	 */
+	protected function getConnection() {
+		if ( !isset( $this->conn ) ) {
+			$conn = false;
+			$servers = $this->ring->getLocations( $this->key, 3 );
+			ArrayUtils::consistentHashSort( $servers, $this->key );
+			foreach ( $servers as $server ) {
+				$conn = $this->pool->getConnection( $this->serversByLabel[$server] );
+				if ( $conn ) {
+					break;
+				}
+			}
+			if ( !$conn ) {
+				return Status::newFatal( 'pool-servererror', implode( ', ', $servers ) );
+			}
+			$this->conn = $conn;
+		}
+		return Status::newGood( $this->conn );
+	}
+
+	function acquireForMe() {
+		$section = new ProfileSection( __METHOD__ );
+
+		return $this->waitForSlotOrNotif( self::AWAKE_ONE );
+	}
+
+	function acquireForAnyone() {
+		$section = new ProfileSection( __METHOD__ );
+
+		return $this->waitForSlotOrNotif( self::AWAKE_ALL );
+	}
+
+	function release() {
+		$section = new ProfileSection( __METHOD__ );
+
+		if ( $this->slot === null ) {
+			return Status::newGood( PoolCounter::NOT_LOCKED ); // not locked
+		}
+
+		$status = $this->getConnection();
+		if ( !$status->isOK() ) {
+			return $status;
+		}
+		$conn = $status->value;
+
+		static $script =
+<<<LUA
+		local kSlots,kSlotsNextRelease,kWakeup,kWaiting = unpack(KEYS)
+		local rMaxWorkers,rExpiry,rSlot,rSlotTime,rAwakeAll,rTime = unpack(ARGV)
+		-- Add the slots back to the list (if rSlot is "w" then it is not a slot).
+		-- Treat the list as expired if the "next release" time sorted-set is missing.
+		if rSlot ~= 'w' and redis.call('exists',kSlotsNextRelease) == 1 then
+			if 1*redis.call('zScore',kSlotsNextRelease,rSlot) ~= (rSlotTime + rExpiry) then
+				-- Slot lock expired and was released already
+			elseif redis.call('lLen',kSlots) >= 1*rMaxWorkers then
+				-- Slots somehow got out of sync; reset the list for sanity
+				redis.call('del',kSlots,kSlotsNextRelease)
+			elseif redis.call('lLen',kSlots) == (1*rMaxWorkers - 1) and redis.call('zCard',kWaiting) == 0 then
+				-- Slot list will be made full; clear it to save space (it re-inits as needed)
+				-- since nothing is waiting on being unblocked by a push to the list
+				redis.call('del',kSlots,kSlotsNextRelease)
+			else
+				-- Add slot back to pool and update the "next release" time
+				redis.call('rPush',kSlots,rSlot)
+				redis.call('zAdd',kSlotsNextRelease,rTime + 30,rSlot)
+				-- Always keep renewing the expiry on use
+				redis.call('expireAt',kSlots,math.ceil(rTime + rExpiry))
+				redis.call('expireAt',kSlotsNextRelease,math.ceil(rTime + rExpiry))
+			end
+		end
+		-- Update an ephemeral list to wake up other clients that can
+		-- reuse any cached work from this process. Only do this if no
+		-- slots are currently free (e.g. clients could be waiting).
+		if 1*rAwakeAll == 1 then
+			local count = redis.call('zCard',kWaiting)
+			for i = 1,count do
+				redis.call('rPush',kWakeup,'w')
+			end
+			redis.call('pexpire',kWakeup,1)
+		end
+		return 1
+LUA;
+		try {
+			$res = $conn->luaEval( $script,
+				array(
+					$this->getSlotListKey(),
+					$this->getSlotRTimeSetKey(),
+					$this->getWakeupListKey(),
+					$this->getWaitSetKey(),
+					$this->workers,
+					$this->lockTTL,
+					$this->slot,
+					$this->slotTime, // used for CAS-style sanity check
+					( $this->onRelease === self::AWAKE_ALL ) ? 1 : 0,
+					microtime( true )
+				),
+				4 # number of first argument(s) that are keys
+			);
+		} catch ( RedisException $e ) {
+			return Status::newFatal( 'pool-error-unknown', $e->getMessage() );
+		}
+
+		$this->slot = null;
+		$this->slotTime = null;
+		$this->onRelease = null;
+		unset( self::$active[$this->session] );
+
+		return Status::newGood( PoolCounter::RELEASED );
+	}
+
+	/**
+	 * @param int $doWakeup AWAKE_* constant
+	 * @return Status
+	 */
+	protected function waitForSlotOrNotif( $doWakeup ) {
+		if ( $this->slot !== null ) {
+			return Status::newGood( PoolCounter::LOCK_HELD ); // already acquired
+		}
+
+		$status = $this->getConnection();
+		if ( !$status->isOK() ) {
+			return $status;
+		}
+		$conn = $status->value;
+
+		$now = microtime( true );
+		try {
+			$slot = $this->initAndPopPoolSlotList( $conn, $now );
+			if ( ctype_digit( $slot ) ) {
+				// Pool slot acquired by this process
+				$slotTime = $now;
+			} elseif ( $slot === 'QUEUE_FULL' ) {
+				// Too many processes are waiting for pooled processes to finish
+				return Status::newGood( PoolCounter::QUEUE_FULL );
+			} elseif ( $slot === 'QUEUE_WAIT' ) {
+				// This process is now registered as waiting
+				$keys = ( $doWakeup == self::AWAKE_ALL )
+					// Wait for an open slot or wake-up signal (preferring the later)
+					? array( $this->getWakeupListKey(), $this->getSlotListKey() )
+					// Just wait for an actual pool slot
+					: array( $this->getSlotListKey() );
+
+				$res = $conn->blPop( $keys, $this->timeout );
+				if ( $res === array() ) {
+					$conn->zRem( $this->getWaitSetKey(), $this->session ); // no longer waiting
+					return Status::newGood( PoolCounter::TIMEOUT );
+				}
+
+				$slot = $res[1]; // pool slot or "w" for wake-up notifications
+				$slotTime = microtime( true ); // last microtime() was a few RTTs ago
+				// Unregister this process as waiting and bump slot "next release" time
+				$this->registerAcquisitionTime( $conn, $slot, $slotTime );
+			} else {
+				return Status::newFatal( 'pool-error-unknown', "Server gave slot '$slot'." );
+			}
+		} catch ( RedisException $e ) {
+			return Status::newFatal( 'pool-error-unknown', $e->getMessage() );
+		}
+
+		if ( $slot !== 'w' ) {
+			$this->slot = $slot;
+			$this->slotTime = $slotTime;
+			$this->onRelease = $doWakeup;
+			self::$active[$this->session] = $this;
+		}
+
+		return Status::newGood( $slot === 'w' ? PoolCounter::DONE : PoolCounter::LOCKED );
+	}
+
+	/**
+	 * @param RedisConnRef $conn
+	 * @param float $now UNIX timestamp
+	 * @return string|bool False on failure
+	 */
+	protected function initAndPopPoolSlotList( RedisConnRef $conn, $now ) {
+		static $script =
+<<<LUA
+		local kSlots,kSlotsNextRelease,kSlotWaits = unpack(KEYS)
+		local rMaxWorkers,rMaxQueue,rTimeout,rExpiry,rSess,rTime = unpack(ARGV)
+		-- Initialize if the "next release" time sorted-set is empty. The slot key
+		-- itself is empty if all slots are busy or when nothing is initialized.
+		-- If the list is empty but the set is not, then it is the later case.
+		-- For sanity, if the list exists but not the set, then reset everything.
+		if redis.call('exists',kSlotsNextRelease) == 0 then
+			redis.call('del',kSlots)
+			for i = 1,1*rMaxWorkers do
+				redis.call('rPush',kSlots,i)
+				redis.call('zAdd',kSlotsNextRelease,-1,i)
+			end
+		-- Otherwise do maintenance to clean up after network partitions
+		else
+			-- Find stale slot locks and add free them (avoid duplicates for sanity)
+			local staleLocks = redis.call('zRangeByScore',kSlotsNextRelease,0,rTime)
+			for k,slot in ipairs(staleLocks) do
+				redis.call('lRem',kSlots,0,slot)
+				redis.call('rPush',kSlots,slot)
+				redis.call('zAdd',kSlotsNextRelease,rTime + 30,slot)
+			end
+			-- Find stale wait slot entries and remove them
+			redis.call('zRemRangeByScore',kSlotWaits,0,rTime - 2*rTimeout)
+		end
+		local slot
+		-- Try to acquire a slot if possible now
+		if redis.call('lLen',kSlots) > 0 then
+			slot = redis.call('lPop',kSlots)
+			-- Update the slot "next release" time
+			redis.call('zAdd',kSlotsNextRelease,rTime + rExpiry,slot)
+		elseif redis.call('zCard',kSlotWaits) >= 1*rMaxQueue then
+			slot = 'QUEUE_FULL'
+		else
+			slot = 'QUEUE_WAIT'
+			-- Register this process as waiting
+			redis.call('zAdd',kSlotWaits,rTime,rSess)
+			redis.call('expireAt',kSlotWaits,math.ceil(rTime + 2*rTimeout))
+		end
+		-- Always keep renewing the expiry on use
+		redis.call('expireAt',kSlots,math.ceil(rTime + rExpiry))
+		redis.call('expireAt',kSlotsNextRelease,math.ceil(rTime + rExpiry))
+		return slot
+LUA;
+		return $conn->luaEval( $script,
+			array(
+				$this->getSlotListKey(),
+				$this->getSlotRTimeSetKey(),
+				$this->getWaitSetKey(),
+				$this->workers,
+				$this->maxqueue,
+				$this->timeout,
+				$this->lockTTL,
+				$this->session,
+				$now
+			),
+			3 # number of first argument(s) that are keys
+		);
+	}
+
+	/**
+	 * @param RedisConnRef $conn
+	 * @param string $slot
+	 * @param float $now
+	 * @return int|bool False on failure
+	 */
+	protected function registerAcquisitionTime( RedisConnRef $conn, $slot, $now ) {
+		static $script =
+<<<LUA
+		local kSlots,kSlotsNextRelease,kSlotWaits = unpack(KEYS)
+		local rSlot,rExpiry,rSess,rTime = unpack(ARGV)
+		-- If rSlot is 'w' then the client was told to wake up but got no slot
+		if rSlot ~= 'w' then
+			-- Update the slot "next release" time
+			redis.call('zAdd',kSlotsNextRelease,rTime + rExpiry,rSlot)
+			-- Always keep renewing the expiry on use
+			redis.call('expireAt',kSlots,math.ceil(rTime + rExpiry))
+			redis.call('expireAt',kSlotsNextRelease,math.ceil(rTime + rExpiry))
+		end
+		-- Unregister this process as waiting
+		redis.call('zRem',kSlotWaits,rSess)
+		return 1
+LUA;
+		return $conn->luaEval( $script,
+			array(
+				$this->getSlotListKey(),
+				$this->getSlotRTimeSetKey(),
+				$this->getWaitSetKey(),
+				$slot,
+				$this->lockTTL,
+				$this->session,
+				$now
+			),
+			3 # number of first argument(s) that are keys
+		);
+	}
+
+	/**
+	 * @return string
+	 */
+	protected function getSlotListKey() {
+		return "poolcounter:l-slots-{$this->keySha1}-{$this->workers}";
+	}
+
+	/**
+	 * @return string
+	 */
+	protected function getSlotRTimeSetKey() {
+		return "poolcounter:z-renewtime-{$this->keySha1}-{$this->workers}";
+	}
+
+	/**
+	 * @return string
+	 */
+	protected function getWaitSetKey() {
+		return "poolcounter:z-wait-{$this->keySha1}-{$this->workers}";
+	}
+
+	/**
+	 * @return string
+	 */
+	protected function getWakeupListKey() {
+		return "poolcounter:l-wakeup-{$this->keySha1}-{$this->workers}";
+	}
+
+	/**
+	 * Try to make sure that locks get released (even with exceptions and fatals)
+	 */
+	public static function releaseAll() {
+		foreach ( self::$active as $poolCounter ) {
+			try {
+				if ( $poolCounter->slot !== null ) {
+					$poolCounter->release();
+				}
+			} catch ( Exception $e ) {
+			}
+		}
+	}
+}
diff --git a/includes/poolcounter/PoolCounterWork.php b/includes/poolcounter/PoolCounterWork.php
new file mode 100644
index 00000000..c0be7a1b
--- /dev/null
+++ b/includes/poolcounter/PoolCounterWork.php
@@ -0,0 +1,160 @@
+<?php
+/**
+ * Provides of semaphore semantics for restricting the number
+ * of workers that may be concurrently performing the same task.
+ *
+ * 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
+ */
+
+/**
+ * Class for dealing with PoolCounters using class members
+ */
+abstract class PoolCounterWork {
+	/** @var string */
+	protected $type = 'generic';
+	/** @var bool */
+	protected $cacheable = false; // does this override getCachedWork() ?
+
+	/**
+	 * @param string $type The type of PoolCounter to use
+	 * @param string $key Key that identifies the queue this work is placed on
+	 */
+	public function __construct( $type, $key ) {
+		$this->type = $type;
+		$this->poolCounter = PoolCounter::factory( $type, $key );
+	}
+
+	/**
+	 * Actually perform the work, caching it if needed
+	 * @return mixed Work result or false
+	 */
+	abstract public function doWork();
+
+	/**
+	 * Retrieve the work from cache
+	 * @return mixed Work result or false
+	 */
+	public function getCachedWork() {
+		return false;
+	}
+
+	/**
+	 * A work not so good (eg. expired one) but better than an error
+	 * message.
+	 * @return mixed Work result or false
+	 */
+	public function fallback() {
+		return false;
+	}
+
+	/**
+	 * Do something with the error, like showing it to the user.
+	 *
+	 * @param Status $status
+	 *
+	 * @return bool
+	 */
+	public function error( $status ) {
+		return false;
+	}
+
+	/**
+	 * Log an error
+	 *
+	 * @param Status $status
+	 * @return void
+	 */
+	public function logError( $status ) {
+		$key = $this->poolCounter->getKey();
+
+		wfDebugLog( 'poolcounter', "Pool key '$key' ({$this->type}): "
+			. $status->getMessage()->inLanguage( 'en' )->useDatabase( false )->text() );
+	}
+
+	/**
+	 * Get the result of the work (whatever it is), or the result of the error() function.
+	 * This returns the result of the first applicable method that returns a non-false value,
+	 * where the methods are checked in the following order:
+	 *   - a) doWork()       : Applies if the work is exclusive or no another process
+	 *                         is doing it, and on the condition that either this process
+	 *                         successfully entered the pool or the pool counter is down.
+	 *   - b) doCachedWork() : Applies if the work is cacheable and this blocked on another
+	 *                         process which finished the work.
+	 *   - c) fallback()     : Applies for all remaining cases.
+	 * If these all fall through (by returning false), then the result of error() is returned.
+	 *
+	 * @param bool $skipcache
+	 * @return mixed
+	 */
+	public function execute( $skipcache = false ) {
+		if ( $this->cacheable && !$skipcache ) {
+			$status = $this->poolCounter->acquireForAnyone();
+		} else {
+			$status = $this->poolCounter->acquireForMe();
+		}
+
+		if ( !$status->isOK() ) {
+			// Respond gracefully to complete server breakage: just log it and do the work
+			$this->logError( $status );
+			return $this->doWork();
+		}
+
+		switch ( $status->value ) {
+			case PoolCounter::LOCK_HELD:
+				// Better to ignore nesting pool counter limits than to fail.
+				// Assume that the outer pool limiting is reasonable enough.
+				/* no break */
+			case PoolCounter::LOCKED:
+				$result = $this->doWork();
+				$this->poolCounter->release();
+				return $result;
+
+			case PoolCounter::DONE:
+				$result = $this->getCachedWork();
+				if ( $result === false ) {
+					/* That someone else work didn't serve us.
+					 * Acquire the lock for me
+					 */
+					return $this->execute( true );
+				}
+				return $result;
+
+			case PoolCounter::QUEUE_FULL:
+			case PoolCounter::TIMEOUT:
+				$result = $this->fallback();
+
+				if ( $result !== false ) {
+					return $result;
+				}
+				/* no break */
+
+			/* These two cases should never be hit... */
+			case PoolCounter::ERROR:
+			default:
+				$errors = array(
+					PoolCounter::QUEUE_FULL => 'pool-queuefull',
+					PoolCounter::TIMEOUT => 'pool-timeout' );
+
+				$status = Status::newFatal( isset( $errors[$status->value] )
+					? $errors[$status->value]
+					: 'pool-errorunknown' );
+				$this->logError( $status );
+				return $this->error( $status );
+		}
+	}
+}
diff --git a/includes/poolcounter/PoolCounterWorkViaCallback.php b/includes/poolcounter/PoolCounterWorkViaCallback.php
new file mode 100644
index 00000000..af83d2e0
--- /dev/null
+++ b/includes/poolcounter/PoolCounterWorkViaCallback.php
@@ -0,0 +1,92 @@
+<?php
+/**
+ * Provides of semaphore semantics for restricting the number
+ * of workers that may be concurrently performing the same task.
+ *
+ * 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
+ */
+
+/**
+ * Convenience class for dealing with PoolCounters using callbacks
+ * @since 1.22
+ */
+class PoolCounterWorkViaCallback extends PoolCounterWork {
+	/** @var callable */
+	protected $doWork;
+	/** @var callable|null */
+	protected $doCachedWork;
+	/** @var callable|null */
+	protected $fallback;
+	/** @var callable|null */
+	protected $error;
+
+	/**
+	 * Build a PoolCounterWork class from a type, key, and callback map.
+	 *
+	 * The callback map must at least have a callback for the 'doWork' method.
+	 * Additionally, callbacks can be provided for the 'doCachedWork', 'fallback',
+	 * and 'error' methods. Methods without callbacks will be no-ops that return false.
+	 * If a 'doCachedWork' callback is provided, then execute() may wait for any prior
+	 * process in the pool to finish and reuse its cached result.
+	 *
+	 * @param string $type
+	 * @param string $key
+	 * @param array $callbacks Map of callbacks
+	 * @throws MWException
+	 */
+	public function __construct( $type, $key, array $callbacks ) {
+		parent::__construct( $type, $key );
+		foreach ( array( 'doWork', 'doCachedWork', 'fallback', 'error' ) as $name ) {
+			if ( isset( $callbacks[$name] ) ) {
+				if ( !is_callable( $callbacks[$name] ) ) {
+					throw new MWException( "Invalid callback provided for '$name' function." );
+				}
+				$this->$name = $callbacks[$name];
+			}
+		}
+		if ( !isset( $this->doWork ) ) {
+			throw new MWException( "No callback provided for 'doWork' function." );
+		}
+		$this->cacheable = isset( $this->doCachedWork );
+	}
+
+	public function doWork() {
+		return call_user_func_array( $this->doWork, array() );
+	}
+
+	public function getCachedWork() {
+		if ( $this->doCachedWork ) {
+			return call_user_func_array( $this->doCachedWork, array() );
+		}
+		return false;
+	}
+
+	public function fallback() {
+		if ( $this->fallback ) {
+			return call_user_func_array( $this->fallback, array() );
+		}
+		return false;
+	}
+
+	public function error( $status ) {
+		if ( $this->error ) {
+			return call_user_func_array( $this->error, array( $status ) );
+		}
+		return false;
+	}
+}
diff --git a/includes/poolcounter/PoolWorkArticleView.php b/includes/poolcounter/PoolWorkArticleView.php
new file mode 100644
index 00000000..5e7e3912
--- /dev/null
+++ b/includes/poolcounter/PoolWorkArticleView.php
@@ -0,0 +1,208 @@
+<?php
+/**
+ * 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
+ */
+
+class PoolWorkArticleView extends PoolCounterWork {
+	/** @var Page */
+	private $page;
+
+	/** @var string */
+	private $cacheKey;
+
+	/** @var int */
+	private $revid;
+
+	/** @var ParserOptions */
+	private $parserOptions;
+
+	/** @var Content|null */
+	private $content = null;
+
+	/** @var ParserOutput|bool */
+	private $parserOutput = false;
+
+	/** @var bool */
+	private $isDirty = false;
+
+	/** @var Status|bool */
+	private $error = false;
+
+	/**
+	 * @param Page $page
+	 * @param ParserOptions $parserOptions ParserOptions to use for the parse
+	 * @param int $revid ID of the revision being parsed.
+	 * @param bool $useParserCache Whether to use the parser cache.
+	 *   operation.
+	 * @param Content|string $content Content to parse or null to load it; may
+	 *   also be given as a wikitext string, for BC.
+	 */
+	public function __construct( Page $page, ParserOptions $parserOptions,
+		$revid, $useParserCache, $content = null
+	) {
+		if ( is_string( $content ) ) { // BC: old style call
+			$modelId = $page->getRevision()->getContentModel();
+			$format = $page->getRevision()->getContentFormat();
+			$content = ContentHandler::makeContent( $content, $page->getTitle(), $modelId, $format );
+		}
+
+		$this->page = $page;
+		$this->revid = $revid;
+		$this->cacheable = $useParserCache;
+		$this->parserOptions = $parserOptions;
+		$this->content = $content;
+		$this->cacheKey = ParserCache::singleton()->getKey( $page, $parserOptions );
+		parent::__construct( 'ArticleView', $this->cacheKey . ':revid:' . $revid );
+	}
+
+	/**
+	 * Get the ParserOutput from this object, or false in case of failure
+	 *
+	 * @return ParserOutput
+	 */
+	public function getParserOutput() {
+		return $this->parserOutput;
+	}
+
+	/**
+	 * Get whether the ParserOutput is a dirty one (i.e. expired)
+	 *
+	 * @return bool
+	 */
+	public function getIsDirty() {
+		return $this->isDirty;
+	}
+
+	/**
+	 * Get a Status object in case of error or false otherwise
+	 *
+	 * @return Status|bool
+	 */
+	public function getError() {
+		return $this->error;
+	}
+
+	/**
+	 * @return bool
+	 */
+	public function doWork() {
+		global $wgUseFileCache;
+
+		// @todo several of the methods called on $this->page are not declared in Page, but present
+		//        in WikiPage and delegated by Article.
+
+		$isCurrent = $this->revid === $this->page->getLatest();
+
+		if ( $this->content !== null ) {
+			$content = $this->content;
+		} elseif ( $isCurrent ) {
+			// XXX: why use RAW audience here, and PUBLIC (default) below?
+			$content = $this->page->getContent( Revision::RAW );
+		} else {
+			$rev = Revision::newFromTitle( $this->page->getTitle(), $this->revid );
+
+			if ( $rev === null ) {
+				$content = null;
+			} else {
+				// XXX: why use PUBLIC audience here (default), and RAW above?
+				$content = $rev->getContent();
+			}
+		}
+
+		if ( $content === null ) {
+			return false;
+		}
+
+		// Reduce effects of race conditions for slow parses (bug 46014)
+		$cacheTime = wfTimestampNow();
+
+		$time = - microtime( true );
+		$this->parserOutput = $content->getParserOutput(
+			$this->page->getTitle(),
+			$this->revid,
+			$this->parserOptions
+		);
+		$time += microtime( true );
+
+		// Timing hack
+		if ( $time > 3 ) {
+			wfDebugLog( 'slow-parse', sprintf( "%-5.2f %s", $time,
+				$this->page->getTitle()->getPrefixedDBkey() ) );
+		}
+
+		if ( $this->cacheable && $this->parserOutput->isCacheable() && $isCurrent ) {
+			ParserCache::singleton()->save(
+				$this->parserOutput, $this->page, $this->parserOptions, $cacheTime, $this->revid );
+		}
+
+		// Make sure file cache is not used on uncacheable content.
+		// Output that has magic words in it can still use the parser cache
+		// (if enabled), though it will generally expire sooner.
+		if ( !$this->parserOutput->isCacheable() || $this->parserOutput->containsOldMagic() ) {
+			$wgUseFileCache = false;
+		}
+
+		if ( $isCurrent ) {
+			$this->page->doCascadeProtectionUpdates( $this->parserOutput );
+		}
+
+		return true;
+	}
+
+	/**
+	 * @return bool
+	 */
+	public function getCachedWork() {
+		$this->parserOutput = ParserCache::singleton()->get( $this->page, $this->parserOptions );
+
+		if ( $this->parserOutput === false ) {
+			wfDebug( __METHOD__ . ": parser cache miss\n" );
+			return false;
+		} else {
+			wfDebug( __METHOD__ . ": parser cache hit\n" );
+			return true;
+		}
+	}
+
+	/**
+	 * @return bool
+	 */
+	public function fallback() {
+		$this->parserOutput = ParserCache::singleton()->getDirty( $this->page, $this->parserOptions );
+
+		if ( $this->parserOutput === false ) {
+			wfDebugLog( 'dirty', 'dirty missing' );
+			wfDebug( __METHOD__ . ": no dirty cache\n" );
+			return false;
+		} else {
+			wfDebug( __METHOD__ . ": sending dirty output\n" );
+			wfDebugLog( 'dirty', "dirty output {$this->cacheKey}" );
+			$this->isDirty = true;
+			return true;
+		}
+	}
+
+	/**
+	 * @param Status $status
+	 * @return bool
+	 */
+	public function error( $status ) {
+		$this->error = $status;
+		return false;
+	}
+}