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

/**
 * @defgroup Cache BagOStuff
 *
 * Most important classes are:
 *
 * @see ObjectCacheFactory
 * @see WANObjectCache
 * @see BagOStuff
 */

namespace Wikimedia\ObjectCache;

use InvalidArgumentException;
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use Wikimedia\LightweightObjectStore\ExpirationAwareness;
use Wikimedia\LightweightObjectStore\StorageAwareness;
use Wikimedia\ScopedCallback;
use Wikimedia\Stats\StatsFactory;

/**
 * Abstract class for any ephemeral data store
 *
 * Class instances should be created with an intended access scope for the dataset, 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 php-apcu 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 that the configuration for those factory methods match their access scope.
 * BagOStuff subclasses have widely varying levels of support replication features within and
 * among datacenters.
 *
 * Subclasses should override the default "segmentationSize" field with an appropriate value.
 * The value should not be larger than what the backing store (by default) supports. It also
 * should be roughly informed by common performance bottlenecks (e.g. values over a certain size
 * having poor scalability). The same goes for the "segmentedValueMaxSize" member, which limits
 * the maximum size and chunk count (indirectly) of values.
 *
 * A few notes about data consistency for BagOStuff instances:
 *  - Read operation methods, e.g. get(), should be synchronous in the local datacenter.
 *    When used with READ_LATEST, such operations should reflect any prior writes originating
 *    from the local datacenter (e.g. by avoiding replica DBs or invoking quorom reads).
 *  - Write operation methods, e.g. set(), should be synchronous in the local datacenter, with
 *    asynchronous cross-datacenter replication. This replication can be either "best effort"
 *    or eventually consistent. If the write succeeded, then any subsequent `get()` operations with
 *    READ_LATEST, regardless of datacenter, should reflect the changes.
 *  - Locking operation methods, e.g. lock(), unlock(), and getScopedLock(), should only apply
 *    to the local datacenter.
 *  - Any set of single-key write operation method calls originating from a single datacenter
 *    should observe "best effort" linearizability.
 *    In this context, "best effort" means that consistency holds as long as connectivity is
 *    strong, network latency is low, and there are no relevant storage server failures.
 *    Per https://en.wikipedia.org/wiki/PACELC_theorem, the store should act as a PA/EL
 *    distributed system for these operations.
 *
 * @stable to extend
 * @newable
 * @ingroup Cache
 * @copyright 2003-2004 Brooke Vibber <bvibber@wikimedia.org>
 */
abstract class BagOStuff implements
        ExpirationAwareness,
        StorageAwareness,
        IStoreKeyEncoder,
        LoggerAwareInterface
{
        /** @var StatsFactory */
        protected $stats;
        /** @var LoggerInterface */
        protected $logger;
        /** @var callable|null */
        protected $asyncHandler;
        /** @var int[] Map of (BagOStuff:ATTR_* constant => BagOStuff:QOS_* constant) */
        protected $attrMap = [];

        /** @var string Default keyspace; used by makeKey() */
        protected $keyspace;

        /** @var int BagOStuff:ERR_* constant of the last error that occurred */
        protected $lastError = self::ERR_NONE;
        /** @var int Error event sequence number of the last error that occurred */
        protected $lastErrorId = 0;

        /** @var int Next sequence number to use for watch/error events */
        protected static $nextErrorMonitorId = 1;

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

        /** Bitfield constants for get()/getMulti(); these are only advisory */
        /** If supported, avoid reading stale data due to replication */
        public const READ_LATEST = 1;
        /** Promise that the caller handles detection of staleness */
        public const READ_VERIFIED = 2;

        /** Bitfield constants for set()/merge(); these are only advisory */
        /** Only change state of the in-memory cache */
        public const WRITE_CACHE_ONLY = 8;
        /** Allow partitioning of the value if it is a large string */
        public const WRITE_ALLOW_SEGMENTS = 16;
        /**
         * Delete all the segments if the value is partitioned
         * @deprecated since 1.43 Use WRITE_ALLOW_SEGMENTS instead.
         */
        public const WRITE_PRUNE_SEGMENTS = self::WRITE_ALLOW_SEGMENTS;
        /**
         * If supported, do not block on write operation completion; instead, treat writes as
         * succesful based on whether they could be buffered. When using this flag with methods
         * that yield item values, the boolean "true" will be used as a placeholder. The next
         * blocking operation (e.g. typical read) will trigger a flush of the operation buffer.
         */
        public const WRITE_BACKGROUND = 64;

        /** Abort after the first merge conflict */
        public const MAX_CONFLICTS_ONE = 1;

        /** @var string Global keyspace; used by makeGlobalKey() */
        protected const GLOBAL_KEYSPACE = 'global';
        /** @var string Precomputed global cache key prefix (needs no encoding) */
        protected const GLOBAL_PREFIX = 'global:';

        /** @var int Item is a single cache key */
        protected const ARG0_KEY = 0;
        /** @var int Item is an array of cache keys */
        protected const ARG0_KEYARR = 1;
        /** @var int Item is an array indexed by cache keys */
        protected const ARG0_KEYMAP = 2;
        /** @var int Item does not involve any keys */
        protected const ARG0_NONKEY = 3;

        /** @var int Item is an array indexed by cache keys */
        protected const RES_KEYMAP = 0;
        /** @var int Item does not involve any keys */
        protected const RES_NONKEY = 1;

        /**
         * @stable to call
         *
         * @param array $params Parameters include:
         *   - keyspace: Keyspace to use for keys in makeKey(). [Default: "local"]
         *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
         *      In CLI mode, it should run the task immediately. [Default: null]
         *   - stats: IStatsdDataFactory instance. [optional]
         *   - logger: \Psr\Log\LoggerInterface instance. [optional]
         *
         * @phan-param array{keyspace?:string,logger?:\Psr\Log\LoggerInterface,asyncHandler?:callable} $params
         */
        public function __construct( array $params = [] ) {
                $this->keyspace = $params['keyspace'] ?? 'local';
                $this->stats = $params['stats'] ?? StatsFactory::newNull();
                $this->setLogger( $params['logger'] ?? new NullLogger() );

                $asyncHandler = $params['asyncHandler'] ?? null;
                if ( is_callable( $asyncHandler ) ) {
                        $this->asyncHandler = $asyncHandler;
                }
        }

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

        /**
         * @since 1.35
         * @return LoggerInterface
         */
        public function getLogger(): LoggerInterface {
                return $this->logger;
        }

        /**
         * Get an item, regenerating and setting it if not found
         *
         * The callback can take $exptime as argument by reference and modify it.
         * Nothing is stored nor deleted if the callback returns false.
         *
         * @param string $key
         * @param int $exptime Time-to-live (seconds)
         * @param callable $callback Callback that derives the new value
         * @param int $flags Bitfield of BagOStuff::READ_* or BagOStuff::WRITE_* constants [optional]
         *
         * @return mixed The cached value if found or the result of $callback otherwise
         * @since 1.27
         */
        final public function getWithSetCallback( $key, $exptime, $callback, $flags = 0 ) {
                $value = $this->get( $key, $flags );

                if ( $value === false ) {
                        $value = $callback( $exptime );
                        if ( $value !== false && $exptime >= 0 ) {
                                $this->set( $key, $value, $exptime, $flags );
                        }
                }

                return $value;
        }

        /**
         * Get an item
         *
         * 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]
         *
         * @return mixed Returns false on failure or if the item does not exist
         */
        abstract public function get( $key, $flags = 0 );

        /**
         * 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
         *  If setting WRITE_ALLOW_SEGMENTS, remember to also set it in any delete() calls.
         * @return bool Success
         */
        abstract public function set( $key, $value, $exptime = 0, $flags = 0 );

        /**
         * Delete an item if it exists
         *
         * For large values set with WRITE_ALLOW_SEGMENTS, this only deletes the placeholder
         * key with the segment list. To delete the underlying blobs, include WRITE_ALLOW_SEGMENTS
         * in the flags for delete() as well. While deleting the segment list key has the effect of
         * functionally deleting the key, it leaves unused blobs in storage.
         *
         * The reason that this is not done automatically, is that to delete underlying blobs,
         * requires first fetching the current segment list. Given that 99% of keys don't use
         * WRITE_ALLOW_SEGMENTS, this would be wasteful.
         *
         * @param string $key
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         * @return bool Success (item deleted or not found)
         */
        abstract public function delete( $key, $flags = 0 );

        /**
         * Insert an item if it does not already exist
         *
         * @param string $key
         * @param mixed $value
         * @param int $exptime
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
         *
         * @return bool Success (item created)
         */
        abstract public function add( $key, $value, $exptime = 0, $flags = 0 );

        /**
         * 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 overridden in the callback.
         * Nothing is stored nor deleted if the callback returns false.
         *
         * @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
         */
        abstract public function merge(
                $key,
                callable $callback,
                $exptime = 0,
                $attempts = 10,
                $flags = 0
        );

        /**
         * Change the expiration on an item
         *
         * If an expiry in the past is given then the key will immediately be expired
         *
         * For large values written using WRITE_ALLOW_SEGMENTS, this only changes the TTL of the
         * main segment list key. While lowering the TTL of the segment list key has the effect of
         * functionally lowering the TTL of the key, it might leave unused blobs in cache for longer.
         * Raising the TTL of such keys is not effective, since the expiration of a single segment
         * key effectively expires the entire value.
         *
         * @param string $key
         * @param int $exptime TTL or UNIX timestamp
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
         *
         * @return bool Success (item found and updated)
         * @since 1.28
         */
        abstract public function changeTTL( $key, $exptime = 0, $flags = 0 );

        /**
         * Acquire an advisory lock on a key string, exclusive to the caller
         *
         * @param string $key
         * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
         * @param int $exptime Lock time-to-live in seconds; 1 day maximum [optional]
         * @param string $rclass If this thread already holds the lock, and the lock was acquired
         *  using the same value for this parameter, then return true and use reference counting so
         *  that only the unlock() call from the outermost lock() caller actually releases the lock
         *  (note that only the outermost time-to-live is used) [optional]
         *
         * @return bool Success
         */
        abstract public function lock( $key, $timeout = 6, $exptime = 6, $rclass = '' );

        /**
         * Release an advisory lock on a key string
         *
         * @param string $key
         *
         * @return bool Success
         */
        abstract public function unlock( $key );

        /**
         * 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 $exptime Lock time-to-live [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, $exptime = 30, $rclass = '' ) {
                $exptime = min( $exptime ?: INF, self::TTL_DAY );

                if ( !$this->lock( $key, $timeout, $exptime, $rclass ) ) {
                        return null;
                }

                return new ScopedCallback( function () use ( $key ) {
                        $this->unlock( $key );
                } );
        }

        /**
         * Delete all objects expiring before a certain date
         *
         * @param string|int $timestamp The reference date in MW or TS_UNIX format
         * @param callable|null $progress Optional, a function which will be called
         *     regularly during long-running operations with the percentage progress
         *     as the first parameter. [optional]
         * @param int|float $limit Maximum number of keys to delete [default: INF]
         * @param string|null $tag Tag to purge a single shard only.
         *  This is only supported when server tags are used in configuration.
         *
         * @return bool Success; false if unimplemented
         */
        abstract public function deleteObjectsExpiringBefore(
                $timestamp,
                ?callable $progress = null,
                $limit = INF,
                ?string $tag = null
        );

        /**
         * Get a batch of items
         *
         * @param string[] $keys List of keys
         * @param int $flags Bitfield; supports READ_LATEST [optional]
         *
         * @return mixed[] Map of (key => value) for existing keys
         */
        abstract public function getMulti( array $keys, $flags = 0 );

        /**
         * Set a batch of items
         *
         * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
         *
         * WRITE_BACKGROUND can be used for bulk insertion where the response is not vital
         *
         * @param mixed[] $valueByKey Map of (key => value)
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
         *
         * @return bool Success
         * @since 1.24
         */
        abstract public function setMulti( array $valueByKey, $exptime = 0, $flags = 0 );

        /**
         * Delete a batch of items
         *
         * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
         *
         * WRITE_BACKGROUND can be used for bulk deletion where the response is not vital
         *
         * @param string[] $keys List of keys
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         * @return bool Success (items deleted and/or not found)
         * @since 1.33
         */
        abstract public function deleteMulti( array $keys, $flags = 0 );

        /**
         * Change the expiration of multiple items
         *
         * @see BagOStuff::changeTTL()
         *
         * @param string[] $keys List of keys
         * @param int $exptime TTL or UNIX timestamp
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
         *
         * @return bool Success (all items found and updated)
         * @since 1.34
         */
        abstract public function changeTTLMulti( array $keys, $exptime, $flags = 0 );

        /**
         * Increase the value of the given key (no TTL change) if it exists or create it otherwise
         *
         * This will create the key with the value $init and TTL $exptime instead if not present.
         * Callers should make sure that both ($init - $step) and $exptime are invariants for all
         * operations to any given key. The value of $init should be at least that of $step.
         *
         * The new value is returned, except if the WRITE_BACKGROUND flag is given, in which case
         * the handler may choose to return true to indicate that the operation has been dispatched.
         *
         * @param string $key Key built via makeKey() or makeGlobalKey()
         * @param int $exptime Time-to-live (in seconds) or a UNIX timestamp expiration
         * @param int $step Amount to increase the key value by [default: 1]
         * @param int|null $init Value to initialize the key to if it does not exist [default: $step]
         * @param int $flags Bit field of class WRITE_* constants [optional]
         *
         * @return int|bool New value (or true if asynchronous) on success; false on failure
         * @since 1.24
         */
        abstract public function incrWithInit( $key, $exptime, $step = 1, $init = null, $flags = 0 );

        /**
         * Get a "watch point" token that can be used to get the "last error" to occur after now
         *
         * @return int A token to that can be used with getLastError()
         * @since 1.38
         */
        public function watchErrors() {
                return self::$nextErrorMonitorId++;
        }

        /**
         * Get the "last error" registry
         *
         * The method should be invoked by a caller as part of the following pattern:
         *   - The caller invokes watchErrors() to get a "since token"
         *   - The caller invokes a sequence of cache operation methods
         *   - The caller invokes getLastError() with the "since token"
         *
         * External callers can also invoke this method as part of the following pattern:
         *   - The caller invokes clearLastError()
         *   - The caller invokes a sequence of cache operation methods
         *   - The caller invokes getLastError()
         *
         * @param int $watchPoint Only consider errors from after this "watch point" [optional]
         *
         * @return int BagOStuff:ERR_* constant for the "last error" registry
         * @note Parameters added in 1.38: $watchPoint
         * @since 1.23
         */
        public function getLastError( $watchPoint = 0 ) {
                return ( $this->lastErrorId > $watchPoint ) ? $this->lastError : self::ERR_NONE;
        }

        /**
         * Clear the "last error" registry
         *
         * @since 1.23
         * @deprecated Since 1.38, hard deprecated in 1.43
         */
        public function clearLastError() {
                wfDeprecated( __METHOD__, '1.38' );
                $this->lastError = self::ERR_NONE;
        }

        /**
         * Set the "last error" registry due to a problem encountered during an attempted operation
         *
         * @param int $error BagOStuff:ERR_* constant
         *
         * @since 1.23
         */
        protected function setLastError( $error ) {
                $this->lastError = $error;
                $this->lastErrorId = self::$nextErrorMonitorId++;
        }

        /**
         * Make a cache key from the given components, in the "global" keyspace
         *
         * Global keys are shared with and visible to all sites hosted in the same
         * infrastructure (e.g. cross-wiki within the same wiki farm). Others sites
         * may read the stored value from their requests, and they must be able to
         * correctly compute new values from their own request context.
         *
         * @see BagOStuff::makeKeyInternal
         * @since 1.27
         *
         * @param string $keygroup Key group component, should be under 48 characters.
         * @param string|int ...$components Additional, ordered, key components for entity IDs
         *
         * @return string Colon-separated, keyspace-prepended, ordered list of encoded components
         */
        public function makeGlobalKey( $keygroup, ...$components ) {
                return $this->makeKeyInternal( self::GLOBAL_KEYSPACE, func_get_args() );
        }

        /**
         * Make a cache key from the given components, in the default keyspace
         *
         * The default keyspace is unique to a given site. Subsequent web requests
         * to the same site (e.g. local wiki, or same domain name) will interact
         * with the same keyspace.
         *
         * Requests to other sites hosted on the same infrastructure (e.g. cross-wiki
         * or cross-domain), have their own keyspace that naturally avoids conflicts.
         *
         * As caller you are responsible for:
         * - Limit the key group (first component) to 48 characters
         *
         * Internally, the colon is used as delimiter (":"), and this is
         * automatically escaped in supplied components to avoid ambiguity or
         * key conflicts. BagOStuff subclasses are responsible for applying any
         * additional escaping or limits as-needed before sending commands over
         * the network.
         *
         * @see BagOStuff::makeKeyInternal
         * @since 1.27
         *
         * @param string $keygroup Key group component, should be under 48 characters.
         * @param string|int ...$components Additional, ordered, key components for entity IDs
         *
         * @return string Colon-separated, keyspace-prepended, ordered list of encoded components
         */
        public function makeKey( $keygroup, ...$components ) {
                return $this->makeKeyInternal( $this->keyspace, func_get_args() );
        }

        /**
         * Check whether a cache key is in the global keyspace
         *
         * @param string $key
         *
         * @return bool
         * @since 1.35
         */
        public function isKeyGlobal( $key ) {
                return str_starts_with( $key, self::GLOBAL_PREFIX );
        }

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

        /**
         * @deprecated since 1.43, not used anywhere.
         * @return int|float The chunk size, in bytes, of segmented objects (INF for no limit)
         * @since 1.34
         */
        public function getSegmentationSize() {
                wfDeprecated( __METHOD__, '1.43' );

                return INF;
        }

        /**
         * @deprecated since 1.43, not used anywhere.
         * @return int|float Maximum total segmented object size in bytes (INF for no limit)
         * @since 1.34
         */
        public function getSegmentedValueMaxSize() {
                wfDeprecated( __METHOD__, '1.43' );

                return INF;
        }

        /**
         * @param int $field
         * @param int $flags
         *
         * @return bool
         * @since 1.34
         */
        final protected function fieldHasFlags( $field, $flags ) {
                return ( ( $field & $flags ) === $flags );
        }

        /**
         * 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)
         */
        final 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;
        }

        /**
         * Make a cache key for the given keyspace and components
         *
         * Subclasses may override this method in order to apply different escaping,
         * or to deal with size constraints (such as MemcachedBagOStuff). For example
         * by converting long components into hashes.
         *
         * If you override this method, you MUST override ::requireConvertGenericKey()
         * to return true. This ensures that wrapping classes (e.g. MultiWriteBagOStuff)
         * know to re-encode keys before calling read/write methods. See also ::proxyCall().
         *
         * @see BagOStuff::proxyCall
         * @since 1.27
         *
         * @param string $keyspace
         * @param string[]|int[] $components Key group and other components
         *
         * @return string
         */
        protected function makeKeyInternal( $keyspace, $components ) {
                if ( count( $components ) < 1 ) {
                        throw new InvalidArgumentException( "Missing key group" );
                }

                $key = $keyspace;
                foreach ( $components as $component ) {
                        // Escape delimiter (":") and escape ("%") characters
                        $key .= ':' . strtr( $component, [ '%' => '%25', ':' => '%3A' ] );
                }

                return $key;
        }

        /**
         * Whether ::proxyCall() must re-encode cache keys before calling read/write methods.
         *
         * @stable to override
         * @see BagOStuff::makeKeyInternal
         * @see BagOStuff::proxyCall
         * @since 1.41
         * @return bool
         */
        protected function requireConvertGenericKey(): bool {
                return false;
        }

        /**
         * Convert a key from BagOStuff::makeKeyInternal into one for the current subclass
         *
         * @see BagOStuff::proxyCall
         *
         * @param string $key Result from BagOStuff::makeKeyInternal
         *
         * @return string Result from current subclass override of BagOStuff::makeKeyInternal
         */
        private function convertGenericKey( $key ) {
                if ( !$this->requireConvertGenericKey() ) {
                        // If subclass doesn't overwrite makeKeyInternal, no re-encoding is needed.
                        return $key;
                }

                // Extract the components from a "generic" key formatted by BagOStuff::makeKeyInternal()
                // Note that the order of each corresponding search/replace pair matters!
                $components = str_replace( [ '%3A', '%25' ], [ ':', '%' ], explode( ':', $key ) );
                if ( count( $components ) < 2 ) {
                        // Legacy key, not even formatted by makeKey()/makeGlobalKey(). Keep as-is.
                        return $key;
                }

                $keyspace = array_shift( $components );

                return $this->makeKeyInternal( $keyspace, $components );
        }

        /**
         * Call a method on behalf of wrapper BagOStuff instance
         *
         * The "wrapper" BagOStuff subclass that calls proxyCall() MUST NOT override
         * the default makeKeyInternal() implementation, because proxyCall() needs
         * to turn the "generic" key back into an array, and re-format it according
         * to the backend-specific BagOStuff::makeKey implementation.
         *
         * For example, when using MultiWriteBagOStuff with Memcached as a backend,
         * writes will go via MemcachedBagOStuff::proxyCall(), which then reformats
         * the "generic" result of BagOStuff::makeKey (called as MultiWriteBagOStuff::makeKey)
         * using MemcachedBagOStuff::makeKeyInternal.
         *
         * @param string $method Name of a non-final public method that reads/changes keys
         * @param int $arg0Sig BagOStuff::ARG0_* constant describing argument 0
         * @param int $resSig BagOStuff::RES_* constant describing the return value
         * @param array $genericArgs Method arguments passed to the wrapper instance
         * @param BagOStuff $wrapper The wrapper BagOStuff instance using this result
         *
         * @return mixed Method result with any keys remapped to "generic" keys
         */
        protected function proxyCall(
                string $method,
                int $arg0Sig,
                int $resSig,
                array $genericArgs,
                BagOStuff $wrapper
        ) {
                // Get the corresponding store-specific cache keys...
                $storeArgs = $genericArgs;
                switch ( $arg0Sig ) {
                        case self::ARG0_KEY:
                                $storeArgs[0] = $this->convertGenericKey( $genericArgs[0] );
                                break;
                        case self::ARG0_KEYARR:
                                foreach ( $genericArgs[0] as $i => $genericKey ) {
                                        $storeArgs[0][$i] = $this->convertGenericKey( $genericKey );
                                }
                                break;
                        case self::ARG0_KEYMAP:
                                $storeArgs[0] = [];
                                foreach ( $genericArgs[0] as $genericKey => $v ) {
                                        $storeArgs[0][$this->convertGenericKey( $genericKey )] = $v;
                                }
                                break;
                }

                // Result of invoking the method with the corresponding store-specific cache keys
                $watchPoint = $this->watchErrors();
                $storeRes = $this->$method( ...$storeArgs );
                $lastError = $this->getLastError( $watchPoint );
                if ( $lastError !== self::ERR_NONE ) {
                        $wrapper->setLastError( $lastError );
                }

                // Convert any store-specific cache keys in the result back to generic cache keys
                if ( $resSig === self::RES_KEYMAP ) {
                        // Map of (store-specific cache key => generic cache key)
                        $genericKeyByStoreKey = array_combine( $storeArgs[0], $genericArgs[0] );

                        $genericRes = [];
                        foreach ( $storeRes as $storeKey => $value ) {
                                $genericRes[$genericKeyByStoreKey[$storeKey]] = $value;
                        }
                } else {
                        $genericRes = $storeRes;
                }

                return $genericRes;
        }

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

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

/** @deprecated class alias since 1.43 */
class_alias( BagOStuff::class, 'BagOStuff' );