Merge "DatabaseMssql: Don't duplicate body of makeList()"

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

<?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/
 *
 * 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
 * </code>
 *
 * @ingroup Cache
 */
abstract class BagOStuff implements LoggerAwareInterface {
        private $debugMode = false;

        protected $lastError = self::ERR_NONE;

        /**
         * @var LoggerInterface
         */
        protected $logger;

        /** 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

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

        /**
         * @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. Returns false if it does not exist.
         * @param string $key
         * @param mixed $casToken [optional]
         * @return mixed Returns false on failure
         */
        abstract public function get( $key, &$casToken = null );

        /**
         * Set an item.
         * @param string $key
         * @param mixed $value
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @return bool Success
         */
        abstract public function set( $key, $value, $exptime = 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 (possibly false),
         * and takes the arguments: (this BagOStuff object, 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
         */
        public function merge( $key, $callback, $exptime = 0, $attempts = 10 ) {
                if ( !is_callable( $callback ) ) {
                        throw new Exception( "Got invalid callback." );
                }

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

        /**
         * @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 {
                        $casToken = null; // passed by reference
                        $currentValue = $this->get( $key, $casToken );
                        // Derive the new value from the old value
                        $value = call_user_func( $callback, $this, $key, $currentValue );

                        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, $exptime );
                        }
                } while ( !$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
         */
        abstract protected function cas( $casToken, $key, $value, $exptime = 0 );

        /**
         * @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 mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10 ) {
                if ( !$this->lock( $key, 6 ) ) {
                        return false;
                }

                $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
                } else {
                        $success = $this->set( $key, $value, $exptime ); // set the new value
                }

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

                return $success;
        }

        /**
         * @param string $key
         * @param int $timeout Lock wait timeout [optional]
         * @param int $expiry Lock expiry [optional]
         * @return bool Success
         */
        public function lock( $key, $timeout = 6, $expiry = 6 ) {
                $this->clearLastError();
                $timestamp = microtime( true ); // starting UNIX timestamp
                if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
                        return true;
                } elseif ( $this->getLastError() ) {
                        return false;
                }

                $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 );

                return $locked;
        }

        /**
         * @param string $key
         * @return bool Success
         */
        public function unlock( $key ) {
                return $this->delete( "{$key}:lock" );
        }

        /**
         * 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;
        }

        /* *** Emulated functions *** */

        /**
         * Get an associative array containing the item for each of the keys that have items.
         * @param array $keys List of strings
         * @return array
         */
        public function getMulti( array $keys ) {
                $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
         */
        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 if not present
         *
         * @param string $key
         * @param int $ttl
         * @param int $value
         * @param int $init
         * @return bool
         * @since 1.24
         */
        public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
                return $this->incr( $key, $value ) ||
                        $this->add( $key, (int)$init, $ttl ) || $this->incr( $key, $value );
        }

        /**
         * 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;
        }

        /**
         * @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 < 86400 * 3650 /* 10 years */ ) ) {
                        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 >= 86400 * 3650 /* 10 years */ ) {
                        $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 ) );
        }
}