[lhc/web/wiklou.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;
use Wikimedia\ScopedCallback;
use Wikimedia\WaitConditionLoop;

/**
 * Class representing a cache/ephemeral data store
 *
 * This interface is intended to be more or less compatible with the PHP memcached client.
 *
 * Instances of this class should be created with an intended access scope, such as:
 *   - a) A single PHP thread on a server (e.g. stored in a PHP variable)
 *   - b) A single application server (e.g. stored in APC or sqlite)
 *   - c) All application servers in datacenter (e.g. stored in memcached or mysql)
 *   - d) All application servers in all datacenters (e.g. stored via mcrouter or dynomite)
 *
 * Callers should use the proper factory methods that yield BagOStuff instances. Site admins
 * should make sure the configuration for those factory methods matches their access scope.
 * BagOStuff subclasses have widely varying levels of support for replication features.
 *
 * For any given instance, methods like lock(), unlock(), merge(), and set() with WRITE_SYNC
 * should semantically operate over its entire access scope; any nodes/threads in that scope
 * should serialize appropriately when using them. Likewise, a call to get() with READ_LATEST
 * from one node in its access scope should reflect the prior changes of any other node its access
 * scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.
 *
 * @ingroup Cache
 */
abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
        /** @var array[] Lock tracking */
        protected $locks = [];
        /** @var int ERR_* class constant */
        protected $lastError = self::ERR_NONE;
        /** @var string */
        protected $keyspace = 'local';
        /** @var LoggerInterface */
        protected $logger;
        /** @var callback|null */
        protected $asyncHandler;
        /** @var int Seconds */
        protected $syncTimeout;

        /** @var bool */
        private $debugMode = false;
        /** @var array */
        private $duplicateKeyLookups = [];
        /** @var bool */
        private $reportDupes = false;
        /** @var bool */
        private $dupeTrackScheduled = false;

        /** @var callable[] */
        protected $busyCallbacks = [];

        /** @var float|null */
        private $wallClockOverride;

        /** @var int[] Map of (ATTR_* class constant => QOS_* class constant) */
        protected $attrMap = [];

        /** 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

        /**
         * $params include:
         *   - logger: Psr\Log\LoggerInterface instance
         *   - keyspace: Default keyspace for $this->makeKey()
         *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
         *      In CLI mode, it should run the task immediately.
         *   - reportDupes: Whether to emit warning log messages for all keys that were
         *      requested more than once (requires an asyncHandler).
         *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
         * @param array $params
         */
        public function __construct( array $params = [] ) {
                if ( isset( $params['logger'] ) ) {
                        $this->setLogger( $params['logger'] );
                } else {
                        $this->setLogger( new NullLogger() );
                }

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

                $this->asyncHandler = $params['asyncHandler'] ?? null;

                if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
                        $this->reportDupes = true;
                }

                $this->syncTimeout = $params['syncTimeout'] ?? 3;
        }

        /**
         * @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 int $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 deterministic 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 int $flags Bitfield of BagOStuff::READ_* constants [optional]
         * @param int $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;

                $this->trackDuplicateKeys( $key );

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

        /**
         * Track the number of times that a given key has been used.
         * @param string $key
         */
        private function trackDuplicateKeys( $key ) {
                if ( !$this->reportDupes ) {
                        return;
                }

                if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
                        // Track that we have seen this key. This N-1 counting style allows
                        // easy filtering with array_filter() later.
                        $this->duplicateKeyLookups[$key] = 0;
                } else {
                        $this->duplicateKeyLookups[$key] += 1;

                        if ( $this->dupeTrackScheduled === false ) {
                                $this->dupeTrackScheduled = true;
                                // Schedule a callback that logs keys processed more than once by get().
                                call_user_func( $this->asyncHandler, function () {
                                        $dups = array_filter( $this->duplicateKeyLookups );
                                        foreach ( $dups as $key => $count ) {
                                                $this->logger->warning(
                                                        'Duplicate get(): "{key}" fetched {count} times',
                                                        // Count is N-1 of the actual lookup count
                                                        [ 'key' => $key, 'count' => $count + 1, ]
                                                );
                                        }
                                } );
                        }
                }
        }

        /**
         * @param string $key
         * @param int $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 int $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, TTL).
         * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
         *
         * @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, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
                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();
                        $reportDupes = $this->reportDupes;
                        $this->reportDupes = false;
                        $casToken = null; // passed by reference
                        $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
                        $this->reportDupes = $reportDupes;

                        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, $exptime );

                        $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();
                $reportDupes = $this->reportDupes;
                $this->reportDupes = false;
                $currentValue = $this->get( $key, self::READ_LATEST );
                $this->reportDupes = $reportDupes;

                if ( $this->getLastError() ) {
                        $success = false;
                } else {
                        // Derive the new value from the old value
                        $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
                        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;
        }

        /**
         * Reset the TTL on a key if it exists
         *
         * @param string $key
         * @param int $expiry
         * @return bool Success Returns false if there is no key
         * @since 1.28
         */
        public function changeTTL( $key, $expiry = 0 ) {
                $value = $this->get( $key );

                return ( $value === false ) ? false : $this->set( $key, $value, $expiry );
        }

        /**
         * 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 );
                $loop = new WaitConditionLoop(
                        function () use ( $key, $timeout, $expiry ) {
                                $this->clearLastError();
                                if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
                                        return true; // locked!
                                } elseif ( $this->getLastError() ) {
                                        return WaitConditionLoop::CONDITION_ABORTED; // network partition?
                                }

                                return WaitConditionLoop::CONDITION_CONTINUE;
                        },
                        $timeout
                );

                $locked = ( $loop->invoke() === $loop::CONDITION_REACHED );
                if ( $locked ) {
                        $this->locks[$key] = [ '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 = $this->getCurrentTime(); // lock timestamp

                return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
                        $latency = 0.050; // latency skew (err towards keeping lock present)
                        $age = ( $this->getCurrentTime() - $lSince + $latency );
                        if ( ( $age + $latency ) >= $expiry ) {
                                $this->logger->warning( "Lock for $key held too long ($age sec)." );
                                return; // expired; it's not "safe" to delete the key
                        }
                        $this->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 int $flags Bitfield; supports READ_LATEST [optional]
         * @return array
         */
        public function getMulti( array $keys, $flags = 0 ) {
                $res = [];
                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;
        }

        /**
         * Let a callback be run to avoid wasting time on special blocking calls
         *
         * The callbacks may or may not be called ever, in any particular order.
         * They are likely to be invoked when something WRITE_SYNC is used used.
         * They should follow a caching pattern as shown below, so that any code
         * using the word will get it's result no matter what happens.
         * @code
         *     $result = null;
         *     $workCallback = function () use ( &$result ) {
         *         if ( !$result ) {
         *             $result = ....
         *         }
         *         return $result;
         *     }
         * @endcode
         *
         * @param callable $workCallback
         * @since 1.28
         */
        public function addBusyCallback( callable $workCallback ) {
                $this->busyCallbacks[] = $workCallback;
        }

        /**
         * 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", [
                                'class' => static::class,
                        ] );
                }
        }

        /**
         * Convert an optionally relative time to an absolute time
         * @param int $exptime
         * @return int
         */
        protected function convertExpiry( $exptime ) {
                if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
                        return (int)$this->getCurrentTime() + $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 ) ) {
                        $exptime -= (int)$this->getCurrentTime();
                        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 Colon-delimited list of $keyspace followed by escaped components of $args
         */
        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 $class Key class
         * @param string $component [optional] Key component (starting with a key collection name)
         * @return string Colon-delimited list of $keyspace followed by escaped components of $args
         */
        public function makeGlobalKey( $class, $component = null ) {
                return $this->makeKeyInternal( 'global', func_get_args() );
        }

        /**
         * Make a cache key, scoped to this instance's keyspace.
         *
         * @since 1.27
         * @param string $class Key class
         * @param string $component [optional] Key component (starting with a key collection name)
         * @return string Colon-delimited list of $keyspace followed by escaped components of $args
         */
        public function makeKey( $class, $component = null ) {
                return $this->makeKeyInternal( $this->keyspace, func_get_args() );
        }

        /**
         * @param int $flag ATTR_* class constant
         * @return int QOS_* class constant
         * @since 1.28
         */
        public function getQoS( $flag ) {
                return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
        }

        /**
         * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
         *
         * @param BagOStuff[] $bags
         * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
         */
        protected function mergeFlagMaps( array $bags ) {
                $map = [];
                foreach ( $bags as $bag ) {
                        foreach ( $bag->attrMap as $attr => $rank ) {
                                if ( isset( $map[$attr] ) ) {
                                        $map[$attr] = min( $map[$attr], $rank );
                                } else {
                                        $map[$attr] = $rank;
                                }
                        }
                }

                return $map;
        }

        /**
         * @return float UNIX timestamp
         * @codeCoverageIgnore
         */
        protected function getCurrentTime() {
                return $this->wallClockOverride ?: microtime( true );
        }

        /**
         * @param float|null &$time Mock UNIX timestamp for testing
         * @codeCoverageIgnore
         */
        public function setMockTime( &$time ) {
                $this->wallClockOverride =& $time;
        }
}