PHPSessionHandler: Implement SessionHandlerInterface

[mediawiki.git] / includes / poolcounter / PoolCounterRedis.php

<?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 PoolCounterRedis[] 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() {
                $status = $this->precheckAcquire();
                if ( !$status->isGood() ) {
                        return $status;
                }

                return $this->waitForSlotOrNotif( self::AWAKE_ONE );
        }

        function acquireForAnyone() {
                $status = $this->precheckAcquire();
                if ( !$status->isGood() ) {
                        return $status;
                }

                return $this->waitForSlotOrNotif( self::AWAKE_ALL );
        }

        function release() {
                if ( $this->slot === null ) {
                        return Status::newGood( PoolCounter::NOT_LOCKED ); // not locked
                }

                $status = $this->getConnection();
                if ( !$status->isOK() ) {
                        return $status;
                }
                $conn = $status->value;

                // @codingStandardsIgnoreStart Generic.Files.LineLength
                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;
                // @codingStandardsIgnoreEnd

                try {
                        $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] );

                $this->onRelease();

                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;
                }

                $this->onAcquire();

                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 ) {
                        }
                }
        }
}