PHPSessionHandler: Implement SessionHandlerInterface

[mediawiki.git] / includes / libs / objectcache / BagOStuff.php

<?php
/**
 * Copyright © 2003-2004 Brion Vibber <brion@pobox.com>
 * https://www.mediawiki.org/
 *
 * 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 Cache
 */

/**
 * @defgroup Cache Cache
 */

use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;

/**
 * interface is intended to be more or less compatible with
 * the PHP memcached client.
 *
 * backends for local hash array and SQL table included:
 * @code
 *   $bag = new HashBagOStuff();
 *   $bag = new SqlBagOStuff(); # connect to db first
 * @endcode
 *
 * @ingroup Cache
 */
abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
        /** @var array[] Lock tracking */
        protected $locks = array();

        /** @var integer */
        protected $lastError = self::ERR_NONE;

        /** @var string */
        protected $keyspace = 'local';

        /** @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
        const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
        /** Bitfield constants for set()/merge() */
        const WRITE_SYNC = 1; // synchronously write to all locations for replicated stores
        const WRITE_CACHE_ONLY = 2; // Only change state of the in-memory cache

        public function __construct( array $params = array() ) {
                if ( isset( $params['logger'] ) ) {
                        $this->setLogger( $params['logger'] );
                } else {
                        $this->setLogger( new NullLogger() );
                }

                if ( isset( $params['keyspace'] ) ) {
                        $this->keyspace = $params['keyspace'];
                }
        }

        /**
         * @param LoggerInterface $logger
         * @return null
         */
        public function setLogger( LoggerInterface $logger ) {
                $this->logger = $logger;
        }

        /**
         * @param bool $bool
         */
        public function setDebug( $bool ) {
                $this->debugMode = $bool;
        }

        /**
         * Get an item with the given key, regenerating and setting it if not found
         *
         * If the callback returns false, then nothing is stored.
         *
         * @param string $key
         * @param int $ttl Time-to-live (seconds)
         * @param callable $callback Callback that derives the new value
         * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
         * @return mixed The cached value if found or the result of $callback otherwise
         * @since 1.27
         */
        final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
                $value = $this->get( $key, $flags );

                if ( $value === false ) {
                        if ( !is_callable( $callback ) ) {
                                throw new InvalidArgumentException( "Invalid cache miss callback provided." );
                        }
                        $value = call_user_func( $callback );
                        if ( $value !== false ) {
                                $this->set( $key, $value, $ttl );
                        }
                }

                return $value;
        }

        /**
         * Get an item with the given key
         *
         * If the key includes a determistic input hash (e.g. the key can only have
         * the correct value) or complete staleness checks are handled by the caller
         * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
         * This lets tiered backends know they can safely upgrade a cached value to
         * higher tiers using standard TTLs.
         *
         * @param string $key
         * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
         * @param integer $oldFlags [unused]
         * @return mixed Returns false on failure and if the item does not exist
         */
        public function get( $key, $flags = 0, $oldFlags = null ) {
                // B/C for ( $key, &$casToken = null, $flags = 0 )
                $flags = is_int( $oldFlags ) ? $oldFlags : $flags;

                return $this->doGet( $key, $flags );
        }

        /**
         * @param string $key
         * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
         * @return mixed Returns false on failure and if the item does not exist
         */
        abstract protected function doGet( $key, $flags = 0 );

        /**
         * @note: This method is only needed if merge() uses mergeViaCas()
         *
         * @param string $key
         * @param mixed $casToken
         * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
         * @return mixed Returns false on failure and if the item does not exist
         * @throws Exception
         */
        protected function getWithToken( $key, &$casToken, $flags = 0 ) {
                throw new Exception( __METHOD__ . ' not implemented.' );
        }

        /**
         * Set an item
         *
         * @param string $key
         * @param mixed $value
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         * @return bool Success
         */
        abstract public function set( $key, $value, $exptime = 0, $flags = 0 );

        /**
         * Delete an item
         *
         * @param string $key
         * @return bool True if the item was deleted or not found, false on failure
         */
        abstract public function delete( $key );

        /**
         * Merge changes into the existing cache value (possibly creating a new one).
         * 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
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         * @return bool Success
         * @throws InvalidArgumentException
         */
        public function merge( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
                if ( !is_callable( $callback ) ) {
                        throw new InvalidArgumentException( "Got invalid callback." );
                }

                return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
        }

        /**
         * @see BagOStuff::merge()
         *
         * @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
         */
        protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
                do {
                        $this->clearLastError();
                        $casToken = null; // passed by reference
                        $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
                        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 ) {
                                // Try to create the key, failing if it gets created in the meantime
                                $success = $this->add( $key, $value, $exptime );
                        } else {
                                // 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;
        }

        /**
         * Check and set an item
         *
         * @param mixed $casToken
         * @param string $key
         * @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__ );
        }

        /**
         * @see BagOStuff::merge()
         *
         * @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
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         * @return bool Success
         */
        protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
                if ( !$this->lock( $key, 6 ) ) {
                        return false;
                }

                $this->clearLastError();
                $currentValue = $this->get( $key, self::READ_LATEST );
                if ( $this->getLastError() ) {
                        $success = false;
                } else {
                        // 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, $flags ); // set the new value
                        }
                }

                if ( !$this->unlock( $key ) ) {
                        // this should never happen
                        trigger_error( "Could not release lock for key '$key'." );
                }

                return $success;
        }

        /**
         * 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; 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, $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, self::TTL_DAY );

                $this->clearLastError();
                $timestamp = microtime( true ); // starting UNIX timestamp
                if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
                        $locked = true;
                } elseif ( $this->getLastError() || $timeout <= 0 ) {
                        $locked = false; // network partition or non-blocking
                } else {
                        // Estimate the RTT (us); use 1ms minimum for sanity
                        $uRTT = max( 1e3, ceil( 1e6 * ( microtime( true ) - $timestamp ) ) );
                        $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 );
                }

                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 ) {
                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, self::TTL_DAY );

                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 );
                } );
        }

        /**
         * Delete all objects expiring before a certain date.
         * @param string $date The reference date in MW format
         * @param callable|bool $progressCallback Optional, a function which will be called
         *     regularly during long-running operations with the percentage progress
         *     as the first parameter.
         *
         * @return bool Success, false if unimplemented
         */
        public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
                // stub
                return false;
        }

        /**
         * 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, $flags = 0 ) {
                $res = array();
                foreach ( $keys as $key ) {
                        $val = $this->get( $key );
                        if ( $val !== false ) {
                                $res[$key] = $val;
                        }
                }
                return $res;
        }

        /**
         * Batch insertion
         * @param array $data $key => $value assoc array
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @return bool Success
         * @since 1.24
         */
        public function setMulti( array $data, $exptime = 0 ) {
                $res = true;
                foreach ( $data as $key => $value ) {
                        if ( !$this->set( $key, $value, $exptime ) ) {
                                $res = false;
                        }
                }
                return $res;
        }

        /**
         * @param string $key
         * @param mixed $value
         * @param int $exptime
         * @return bool Success
         */
        public function add( $key, $value, $exptime = 0 ) {
                if ( $this->get( $key ) === false ) {
                        return $this->set( $key, $value, $exptime );
                }
                return false; // key already set
        }

        /**
         * Increase stored value of $key by $value while preserving its TTL
         * @param string $key Key to increase
         * @param int $value Value to add to $key (Default 1)
         * @return int|bool New value or false on failure
         */
        public function incr( $key, $value = 1 ) {
                if ( !$this->lock( $key ) ) {
                        return false;
                }
                $n = $this->get( $key );
                if ( $this->isInteger( $n ) ) { // key exists?
                        $n += intval( $value );
                        $this->set( $key, max( 0, $n ) ); // exptime?
                } else {
                        $n = false;
                }
                $this->unlock( $key );

                return $n;
        }

        /**
         * Decrease stored value of $key by $value while preserving its TTL
         * @param string $key
         * @param int $value
         * @return int|bool New value or false on failure
         */
        public function decr( $key, $value = 1 ) {
                return $this->incr( $key, - $value );
        }

        /**
         * Increase stored value of $key by $value while preserving its TTL
         *
         * This will create the key with value $init and TTL $ttl instead if not present
         *
         * @param string $key
         * @param int $ttl
         * @param int $value
         * @param int $init
         * @return int|bool New value or false on failure
         * @since 1.24
         */
        public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
                $newValue = $this->incr( $key, $value );
                if ( $newValue === false ) {
                        // No key set; initialize
                        $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
                }
                if ( $newValue === false ) {
                        // Raced out initializing; increment
                        $newValue = $this->incr( $key, $value );
                }

                return $newValue;
        }

        /**
         * Get the "last error" registered; clearLastError() should be called manually
         * @return int ERR_* constant for the "last error" registry
         * @since 1.23
         */
        public function getLastError() {
                return $this->lastError;
        }

        /**
         * Clear the "last error" registry
         * @since 1.23
         */
        public function clearLastError() {
                $this->lastError = self::ERR_NONE;
        }

        /**
         * Set the "last error" registry
         * @param int $err ERR_* constant
         * @since 1.23
         */
        protected function setLastError( $err ) {
                $this->lastError = $err;
        }

        /**
         * 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 ) {
                if ( $this->debugMode ) {
                        $this->logger->debug( "{class} debug: $text", array(
                                'class' => get_class( $this ),
                        ) );
                }
        }

        /**
         * Convert an optionally relative time to an absolute time
         * @param int $exptime
         * @return int
         */
        protected function convertExpiry( $exptime ) {
                if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
                        return time() + $exptime;
                } else {
                        return $exptime;
                }
        }

        /**
         * Convert an optionally absolute expiry time to a relative time. If an
         * absolute time is specified which is in the past, use a short expiry time.
         *
         * @param int $exptime
         * @return int
         */
        protected function convertToRelative( $exptime ) {
                if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
                        $exptime -= time();
                        if ( $exptime <= 0 ) {
                                $exptime = 1;
                        }
                        return $exptime;
                } else {
                        return $exptime;
                }
        }

        /**
         * Check if a value is an integer
         *
         * @param mixed $value
         * @return bool
         */
        protected function isInteger( $value ) {
                return ( is_int( $value ) || ctype_digit( $value ) );
        }

        /**
         * Construct a cache key.
         *
         * @since 1.27
         * @param string $keyspace
         * @param array $args
         * @return string
         */
        public function makeKeyInternal( $keyspace, $args ) {
                $key = $keyspace;
                foreach ( $args as $arg ) {
                        $arg = str_replace( ':', '%3A', $arg );
                        $key = $key . ':' . $arg;
                }
                return strtr( $key, ' ', '_' );
        }

        /**
         * Make a global cache key.
         *
         * @since 1.27
         * @param string ... Key component (variadic)
         * @return string
         */
        public function makeGlobalKey() {
                return $this->makeKeyInternal( 'global', func_get_args() );
        }

        /**
         * Make a cache key, scoped to this instance's keyspace.
         *
         * @since 1.27
         * @param string ... Key component (variadic)
         * @return string
         */
        public function makeKey() {
                return $this->makeKeyInternal( $this->keyspace, func_get_args() );
        }
}