MediumSpecificBagOStuff.php
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MediumSpecificBagOStuff.php
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	<?php
	/**
	* @license GPL-2.0-or-later
	* @file
	*/
	namespace Wikimedia\ObjectCache;

	use InvalidArgumentException;
	use JsonSerializable;
	use stdClass;
	use Wikimedia\WaitConditionLoop;

	/**
	* Helper classs that implements most of BagOStuff for a backend.
	*
	* This should be used by concrete implementations only. Wrapper classes that
	* proxy another BagOStuff should extend and implement BagOStuff directly.
	*
	* @ingroup Cache
	* @since 1.34
	*/
	abstract class MediumSpecificBagOStuff extends BagOStuff {
	/** @var array<string,array> Map of (key => (class LOCK_* constant => value) */
	protected $locks = [];
	/** @var int Bytes; chunk size of segmented cache values */
	protected $segmentationSize;
	/** @var int Bytes; maximum total size of a segmented cache value */
	protected $segmentedValueMaxSize;

	/** @var float Seconds; maximum expected seconds for a lock ping to reach the backend */
	protected $maxLockSendDelay = 0.05;

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

	/** Component to use for key construction of blob segment keys */
	private const SEGMENT_COMPONENT = 'segment';

	/** Idiom for doGet() to return extra information by reference */
	protected const PASS_BY_REF = -1;

	protected const METRIC_OP_GET = 'get';
	protected const METRIC_OP_SET = 'set';
	protected const METRIC_OP_DELETE = 'delete';
	protected const METRIC_OP_CHANGE_TTL = 'change_ttl';
	protected const METRIC_OP_ADD = 'add';
	protected const METRIC_OP_INCR = 'incr';
	protected const METRIC_OP_DECR = 'decr';
	protected const METRIC_OP_CAS = 'cas';

	protected const LOCK_RCLASS = 0;
	protected const LOCK_DEPTH = 1;
	protected const LOCK_TIME = 2;
	protected const LOCK_EXPIRY = 3;

	/**
	* @see BagOStuff::__construct()
	* Additional $params options include:
	* - logger: Psr\Log\LoggerInterface instance
	* - reportDupes: Whether to emit warning log messages for all keys that were
	* requested more than once (requires an asyncHandler).
	* - segmentationSize: The chunk size, in bytes, of segmented values. The value should
	* not exceed the maximum size of values in the storage backend, as configured by
	* the site administrator.
	* - segmentedValueMaxSize: The maximum total size, in bytes, of segmented values.
	* This should be configured to a reasonable size give the site traffic and the
	* amount of I/O between application and cache servers that the network can handle.
	*
	* @param array $params
	*
	* @phpcs:ignore Generic.Files.LineLength
	* @phan-param array{logger?:\Psr\Log\LoggerInterface,asyncHandler?:callable,reportDupes?:bool,segmentationSize?:int\|float,segmentedValueMaxSize?:int} $params
	*/
	public function __construct( array $params = [] ) {
	parent::__construct( $params );

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

	// Default to 8MiB if segmentationSize is not set
	$this->segmentationSize = $params['segmentationSize'] ?? 8_388_608;
	// Default to 64MiB if segmentedValueMaxSize is not set
	$this->segmentedValueMaxSize = $params['segmentedValueMaxSize'] ?? 67_108_864;
	}

	/**
	* 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]
	*
	* @return mixed Returns false on failure or if the item does not exist
	*/
	public function get( $key, $flags = 0 ) {
	$this->trackDuplicateKeys( $key );

	return $this->resolveSegments( $key, $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]++;

	if ( $this->dupeTrackScheduled === false ) {
	$this->dupeTrackScheduled = true;
	// Schedule a callback that logs keys processed more than once by get().
	( $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, ]
	);
	}
	} );
	}
	}
	}

	/**
	* Get an item
	*
	* The CAS token should be null if the key does not exist or the value is corrupt
	*
	* @param string $key
	* @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
	* @param mixed &$casToken CAS token if MediumSpecificBagOStuff::PASS_BY_REF [returned]
	*
	* @return mixed Returns false on failure or if the item does not exist
	*/
	abstract protected function doGet( $key, $flags = 0, &$casToken = null );

	/** @inheritDoc */
	public function set( $key, $value, $exptime = 0, $flags = 0 ) {
	$entry = $this->makeValueOrSegmentList( $key, $value, $exptime, $flags, $ok );

	// Only when all segments (if any) are stored should the main key be changed
	return $ok && $this->doSet( $key, $entry, $exptime, $flags );
	}

	/**
	* 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 protected function doSet( $key, $value, $exptime = 0, $flags = 0 );

	/** @inheritDoc */
	public function delete( $key, $flags = 0 ) {
	if ( !$this->fieldHasFlags( $flags, self::WRITE_ALLOW_SEGMENTS ) ) {
	return $this->doDelete( $key, $flags );
	}

	$mainValue = $this->doGet( $key, self::READ_LATEST );
	if ( !$this->doDelete( $key, $flags ) ) {
	return false;
	}

	if ( !SerializedValueContainer::isSegmented( $mainValue ) ) {
	// no segments to delete
	return true;
	}

	$orderedKeys = array_map(
	function ( $segmentHash ) use ( $key ) {
	return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
	},
	$mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
	);

	return $this->deleteMulti( $orderedKeys, $flags & ~self::WRITE_ALLOW_SEGMENTS );
	}

	/**
	* Delete an item
	*
	* @param string $key
	* @param int $flags Bitfield of BagOStuff::WRITE_* constants
	*
	* @return bool True if the item was deleted or not found, false on failure
	*/
	abstract protected function doDelete( $key, $flags = 0 );

	/** @inheritDoc */
	public function add( $key, $value, $exptime = 0, $flags = 0 ) {
	$entry = $this->makeValueOrSegmentList( $key, $value, $exptime, $flags, $ok );

	// Only when all segments (if any) are stored should the main key be changed
	return $ok && $this->doAdd( $key, $entry, $exptime, $flags );
	}

	/**
	* 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
	*/
	abstract protected function doAdd( $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
	*/
	public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
	return $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
	}

	/**
	* @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
	* @see BagOStuff::merge()
	*/
	final protected function mergeViaCas( $key, callable $callback, $exptime, $attempts, $flags ) {
	$attemptsLeft = $attempts;
	do {
	$token = self::PASS_BY_REF;
	// Get the old value and CAS token from cache
	$watchPoint = $this->watchErrors();
	$currentValue = $this->resolveSegments(
	$key,
	$this->doGet( $key, $flags, $token )
	);
	if ( $this->getLastError( $watchPoint ) ) {
	// Don't spam slow retries due to network problems (retry only on races)
	$this->logger->warning(
	__METHOD__ . ' failed due to read I/O error on get() for {key}.', [ 'key' => $key ]
	);
	$success = false;
	break;
	}

	// Derive the new value from the old value
	$value = $callback( $this, $key, $currentValue, $exptime );
	$keyWasNonexistent = ( $currentValue === false );
	$valueMatchesOldValue = ( $value === $currentValue );
	// free RAM in case the value is large
	unset( $currentValue );

	$watchPoint = $this->watchErrors();
	if ( $value === false \|\| $exptime < 0 ) {
	// do nothing
	$success = true;
	} elseif ( $valueMatchesOldValue && $attemptsLeft !== $attempts ) {
	// recently set by another thread to the same value
	$success = true;
	} elseif ( $keyWasNonexistent ) {
	// Try to create the key, failing if it gets created in the meantime
	$success = $this->add( $key, $value, $exptime, $flags );
	} else {
	// Try to update the key, failing if it gets changed in the meantime
	$success = $this->cas( $token, $key, $value, $exptime, $flags );
	}
	if ( $this->getLastError( $watchPoint ) ) {
	// Don't spam slow retries due to network problems (retry only on races)
	$this->logger->warning(
	__METHOD__ . ' failed due to write I/O error for {key}.',
	[ 'key' => $key ]
	);
	$success = false;
	break;
	}

	} while ( !$success && --$attemptsLeft );

	return $success;
	}

	/**
	* Set an item if the current CAS token matches the provided CAS token
	*
	* @param mixed $casToken Only set the item if it still has this CAS token
	* @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
	*/
	protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
	if ( $casToken === null ) {
	$this->logger->warning(
	__METHOD__ . ' got empty CAS token for {key}.',
	[ 'key' => $key ]
	);

	// caller may have meant to use add()?
	return false;
	}

	$entry = $this->makeValueOrSegmentList( $key, $value, $exptime, $flags, $ok );

	// Only when all segments (if any) are stored should the main key be changed
	return $ok && $this->doCas( $casToken, $key, $entry, $exptime, $flags );
	}

	/**
	* Set an item if the current CAS token matches the provided CAS token
	*
	* @param mixed $casToken CAS token from an existing version of the key
	* @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
	*/
	protected function doCas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
	// @TODO: the use of lock() assumes that all other relevant sets() use a lock
	if ( !$this->lock( $key, 0 ) ) {
	// non-blocking
	return false;
	}

	$curCasToken = self::PASS_BY_REF;
	$watchPoint = $this->watchErrors();
	$exists = ( $this->doGet( $key, self::READ_LATEST, $curCasToken ) !== false );
	if ( $this->getLastError( $watchPoint ) ) {
	// Fail if the old CAS token could not be read
	$success = false;
	$this->logger->warning(
	__METHOD__ . ' failed due to write I/O error for {key}.',
	[ 'key' => $key ]
	);
	} elseif ( $exists && $this->tokensMatch( $casToken, $curCasToken ) ) {
	$success = $this->doSet( $key, $value, $exptime, $flags );
	} else {
	// mismatched or failed
	$success = false;
	$this->logger->info(
	__METHOD__ . ' failed due to race condition for {key}.',
	[ 'key' => $key, 'key_exists' => $exists ]
	);
	}

	$this->unlock( $key );

	return $success;
	}

	/**
	* @param mixed $value CAS token for an existing key
	* @param mixed $otherValue CAS token for an existing key
	*
	* @return bool Whether the two tokens match
	*/
	final protected function tokensMatch( $value, $otherValue ) {
	$type = gettype( $value );
	// Ideally, tokens are counters, timestamps, hashes, or serialized PHP values.
	// However, some classes might use the PHP values themselves.
	if ( $type !== gettype( $otherValue ) ) {
	return false;
	}
	// Serialize both tokens to strictly compare objects or arrays (which might objects
	// nested inside). Note that this will not apply if integer/string CAS tokens are used.
	if ( $type === 'array' \|\| $type === 'object' ) {
	return ( serialize( $value ) === serialize( $otherValue ) );
	}

	// For string/integer tokens, use a simple comparison
	return ( $value === $otherValue );
	}

	/**
	* Change the expiration on a key if it exists
	*
	* 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 Returns false on failure or if the item does not exist
	* @since 1.28
	*/
	public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
	return $this->doChangeTTL( $key, $exptime, $flags );
	}

	/**
	* @param string $key
	* @param int $exptime
	* @param int $flags
	*
	* @return bool
	*/
	protected function doChangeTTL( $key, $exptime, $flags ) {
	// @TODO: the use of lock() assumes that all other relevant sets() use a lock
	if ( !$this->lock( $key, 0 ) ) {
	return false;
	}

	$expiry = $this->getExpirationAsTimestamp( $exptime );
	$delete = ( $expiry != self::TTL_INDEFINITE && $expiry < $this->getCurrentTime() );

	// Use doGet() to avoid having to trigger resolveSegments()
	$blob = $this->doGet( $key, self::READ_LATEST );
	if ( $blob ) {
	if ( $delete ) {
	$ok = $this->doDelete( $key, $flags );
	} else {
	$ok = $this->doSet( $key, $blob, $exptime, $flags );
	}
	} else {
	$ok = false;
	}

	$this->unlock( $key );

	return $ok;
	}

	/** @inheritDoc */
	public function incrWithInit( $key, $exptime, $step = 1, $init = null, $flags = 0 ) {
	$step = (int)$step;
	$init = is_int( $init ) ? $init : $step;

	return $this->doIncrWithInit( $key, $exptime, $step, $init, $flags );
	}

	/**
	* @param string $key
	* @param int $exptime
	* @param int $step
	* @param int $init
	* @param int $flags
	*
	* @return int\|bool New value or false on failure
	*/
	abstract protected function doIncrWithInit( $key, $exptime, $step, $init, $flags );

	/**
	* @param string $key
	* @param int $timeout
	* @param int $exptime
	* @param string $rclass
	*
	* @return bool
	*/
	public function lock( $key, $timeout = 6, $exptime = 6, $rclass = '' ) {
	$exptime = min( $exptime ?: INF, self::TTL_DAY );

	$acquired = false;

	if ( isset( $this->locks[$key] ) ) {
	// Already locked; avoid deadlocks and allow lock reentry if specified
	if ( $rclass != '' && $this->locks[$key][self::LOCK_RCLASS] === $rclass ) {
	++$this->locks[$key][self::LOCK_DEPTH];
	$acquired = true;
	}
	} else {
	// Not already locked; acquire a lock on the backend
	$lockTsUnix = $this->doLock( $key, $timeout, $exptime );
	if ( $lockTsUnix !== null ) {
	$this->locks[$key] = [
	self::LOCK_RCLASS => $rclass,
	self::LOCK_DEPTH => 1,
	self::LOCK_TIME => $lockTsUnix,
	self::LOCK_EXPIRY => $lockTsUnix + $exptime
	];
	$acquired = true;
	}
	}

	return $acquired;
	}

	/**
	* @see MediumSpecificBagOStuff::lock()
	*
	* @param string $key
	* @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
	* @param int $exptime Lock time-to-live 1 day maximum [optional]
	*
	* @return float\|null UNIX timestamp of acquisition; null on failure
	*/
	protected function doLock( $key, $timeout, $exptime ) {
	$lockTsUnix = null;

	$fname = __METHOD__;
	$loop = new WaitConditionLoop(
	function () use ( $key, $exptime, $fname, &$lockTsUnix ) {
	$watchPoint = $this->watchErrors();
	if ( $this->add( $this->makeLockKey( $key ), 1, $exptime ) ) {
	$lockTsUnix = microtime( true );

	return WaitConditionLoop::CONDITION_REACHED;
	} elseif ( $this->getLastError( $watchPoint ) ) {
	$this->logger->warning(
	"$fname failed due to I/O error for {key}.",
	[ 'key' => $key ]
	);

	return WaitConditionLoop::CONDITION_ABORTED;
	}

	return WaitConditionLoop::CONDITION_CONTINUE;
	},
	$timeout
	);
	$code = $loop->invoke();

	if ( $code === $loop::CONDITION_TIMED_OUT ) {
	$this->logger->warning(
	"$fname failed due to timeout for {key}.",
	[ 'key' => $key, 'timeout' => $timeout ]
	);
	}

	return $lockTsUnix;
	}

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

	if ( isset( $this->locks[$key] ) ) {
	if ( --$this->locks[$key][self::LOCK_DEPTH] > 0 ) {
	$released = true;
	} else {
	$released = $this->doUnlock( $key );
	unset( $this->locks[$key] );
	if ( !$released ) {
	$this->logger->warning(
	__METHOD__ . ' failed to release lock for {key}.',
	[ 'key' => $key ]
	);
	}
	}
	} else {
	$this->logger->warning(
	__METHOD__ . ' no lock to release for {key}.',
	[ 'key' => $key ]
	);
	}

	return $released;
	}

	/**
	* @see MediumSpecificBagOStuff::unlock()
	*
	* @param string $key
	*
	* @return bool Success
	*/
	protected function doUnlock( $key ) {
	$released = false;

	// Estimate the remaining TTL of the lock key
	$curTTL = $this->locks[$key][self::LOCK_EXPIRY] - $this->getCurrentTime();

	// Check the risk of race conditions for key deletion
	if ( $this->getQoS( self::ATTR_DURABILITY ) <= self::QOS_DURABILITY_SCRIPT ) {
	// Lock (and data) keys use memory specific to this request (e.g. HashBagOStuff)
	$isSafe = true;
	} else {
	// It is unsafe to delete the lock key if there is a serious risk of the key already
	// being claimed by another thread before the delete operation reaches the backend
	$isSafe = ( $curTTL > $this->maxLockSendDelay );
	}

	if ( $isSafe ) {
	$released = $this->doDelete( $this->makeLockKey( $key ) );
	} else {
	$this->logger->warning(
	"Lock for {key} held too long ({age} sec).",
	[ 'key' => $key, 'curTTL' => $curTTL ]
	);
	}

	return $released;
	}

	/**
	* @param string $key
	*
	* @return string
	*/
	protected function makeLockKey( $key ) {
	return "$key:lock";
	}

	/** @inheritDoc */
	public function deleteObjectsExpiringBefore(
	$timestamp,
	?callable $progress = null,
	$limit = INF,
	?string $tag = null
	) {
	return false;
	}

	/**
	* Get an associative array containing the item for each of the keys that have items.
	*
	* @param string[] $keys List of keys; can be a map of (unused => key) for convenience
	* @param int $flags Bitfield; supports READ_LATEST [optional]
	*
	* @return mixed[] Map of (key => value) for existing keys; preserves the order of $keys
	*/
	public function getMulti( array $keys, $flags = 0 ) {
	$foundByKey = $this->doGetMulti( $keys, $flags );

	$res = [];
	foreach ( $keys as $key ) {
	// Resolve one blob at a time (avoids too much I/O at once)
	if ( array_key_exists( $key, $foundByKey ) ) {
	// A value should not appear in the key if a segment is missing
	$value = $this->resolveSegments( $key, $foundByKey[$key] );
	if ( $value !== false ) {
	$res[$key] = $value;
	}
	}
	}

	return $res;
	}

	/**
	* Get an associative array containing the item for each of the keys that have items.
	*
	* @param string[] $keys List of keys
	* @param int $flags Bitfield; supports READ_LATEST [optional]
	*
	* @return array Map of (key => value) for existing keys; preserves the order of $keys
	*/
	protected function doGetMulti( array $keys, $flags = 0 ) {
	$res = [];
	foreach ( $keys as $key ) {
	$val = $this->doGet( $key, $flags );
	if ( $val !== false ) {
	$res[$key] = $val;
	}
	}

	return $res;
	}

	/**
	* Batch insertion/replace
	*
	* This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
	*
	* @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
	*/
	public function setMulti( array $valueByKey, $exptime = 0, $flags = 0 ) {
	if ( $this->fieldHasFlags( $flags, self::WRITE_ALLOW_SEGMENTS ) ) {
	throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
	}

	return $this->doSetMulti( $valueByKey, $exptime, $flags );
	}

	/**
	* @param mixed[] $data 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
	*
	* @return bool Success
	*/
	protected function doSetMulti( array $data, $exptime = 0, $flags = 0 ) {
	$res = true;
	foreach ( $data as $key => $value ) {
	$res = $this->doSet( $key, $value, $exptime, $flags ) && $res;
	}

	return $res;
	}

	/** @inheritDoc */
	public function deleteMulti( array $keys, $flags = 0 ) {
	if ( $this->fieldHasFlags( $flags, self::WRITE_ALLOW_SEGMENTS ) ) {
	throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
	}

	return $this->doDeleteMulti( $keys, $flags );
	}

	/**
	* @param string[] $keys List of keys
	* @param int $flags Bitfield of BagOStuff::WRITE_* constants
	*
	* @return bool Success
	*/
	protected function doDeleteMulti( array $keys, $flags = 0 ) {
	$res = true;
	foreach ( $keys as $key ) {
	$res = $this->doDelete( $key, $flags ) && $res;
	}

	return $res;
	}

	/**
	* Change the expiration of multiple keys that exist
	*
	* @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
	*
	* @since 1.34
	*/
	public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
	return $this->doChangeTTLMulti( $keys, $exptime, $flags );
	}

	/**
	* @param string[] $keys List of keys
	* @param int $exptime TTL or UNIX timestamp
	* @param int $flags Bitfield of BagOStuff::WRITE_* constants
	*
	* @return bool Success
	*/
	protected function doChangeTTLMulti( array $keys, $exptime, $flags = 0 ) {
	$res = true;
	foreach ( $keys as $key ) {
	$res = $this->doChangeTTL( $key, $exptime, $flags ) && $res;
	}

	return $res;
	}

	/**
	* Get and reassemble the chunks of blob at the given key
	*
	* @param string $key
	* @param mixed $mainValue
	*
	* @return string\|null\|bool The combined string, false if missing, null on error
	*/
	final protected function resolveSegments( $key, $mainValue ) {
	if ( SerializedValueContainer::isSegmented( $mainValue ) ) {
	$orderedKeys = array_map(
	function ( $segmentHash ) use ( $key ) {
	return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
	},
	$mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
	);

	$segmentsByKey = $this->doGetMulti( $orderedKeys );

	$parts = [];
	foreach ( $orderedKeys as $segmentKey ) {
	if ( isset( $segmentsByKey[$segmentKey] ) ) {
	$parts[] = $segmentsByKey[$segmentKey];
	} else {
	// missing segment
	return false;
	}
	}

	return $this->unserialize( implode( '', $parts ) );
	}

	return $mainValue;
	}

	/**
	* Check if a value should use a segmentation wrapper due to its size
	*
	* In order to avoid extra serialization and/or twice-serialized wrappers, just check if
	* the value is a large string. Support cache wrappers (e.g. WANObjectCache) that use 2D
	* arrays to wrap values. This does not recurse in order to avoid overhead from complex
	* structures and the risk of infinite loops (due to references).
	*
	* @param mixed $value
	* @param int $flags
	*
	* @return bool
	*/
	private function useSegmentationWrapper( $value, $flags ) {
	if (
	$this->segmentationSize === INF \|\|
	!$this->fieldHasFlags( $flags, self::WRITE_ALLOW_SEGMENTS )
	) {
	return false;
	}

	if ( is_string( $value ) ) {
	return ( strlen( $value ) >= $this->segmentationSize );
	}

	if ( is_array( $value ) ) {
	// Expect that the contained value will be one of the first array entries
	foreach ( array_slice( $value, 0, 4 ) as $v ) {
	if ( is_string( $v ) && strlen( $v ) >= $this->segmentationSize ) {
	return true;
	}
	}
	}

	// Avoid breaking functions for incrementing/decrementing integer key values
	return false;
	}

	/**
	* Make the entry to store at a key (inline or segment list), storing any segments
	*
	* @param string $key
	* @param mixed $value
	* @param int $exptime
	* @param int $flags
	* @param mixed\|null &$ok Whether the entry is usable (e.g. no missing segments) [returned]
	*
	* @return mixed The entry (inline value, wrapped inline value, or wrapped segment list)
	* @since 1.34
	*/
	final protected function makeValueOrSegmentList( $key, $value, $exptime, $flags, &$ok ) {
	$entry = $value;
	$ok = true;

	if ( $this->useSegmentationWrapper( $value, $flags ) ) {
	$segmentSize = $this->segmentationSize;
	$maxTotalSize = $this->segmentedValueMaxSize;
	$serialized = $this->getSerialized( $value, $key );
	$size = strlen( $serialized );
	if ( $size > $maxTotalSize ) {
	$this->logger->warning(
	"Value for {key} exceeds $maxTotalSize bytes; cannot segment.",
	[ 'key' => $key ]
	);
	} else {
	// Split the serialized value into chunks and store them at different keys
	$chunksByKey = [];
	$segmentHashes = [];
	$count = intdiv( $size, $segmentSize ) + ( ( $size % $segmentSize ) ? 1 : 0 );
	for ( $i = 0; $i < $count; ++$i ) {
	$segment = substr( $serialized, $i * $segmentSize, $segmentSize );
	$hash = sha1( $segment );
	$chunkKey = $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $hash );
	$chunksByKey[$chunkKey] = $segment;
	$segmentHashes[] = $hash;
	}
	$flags &= ~self::WRITE_ALLOW_SEGMENTS;
	$ok = $this->setMulti( $chunksByKey, $exptime, $flags );
	$entry = SerializedValueContainer::newSegmented( $segmentHashes );
	}
	}

	return $entry;
	}

	/**
	* @param int\|float $exptime
	*
	* @return bool Whether the expiry is non-infinite, and, negative or not a UNIX timestamp
	* @since 1.34
	*/
	final protected function isRelativeExpiration( $exptime ) {
	return ( $exptime !== self::TTL_INDEFINITE && $exptime < ( 10 * self::TTL_YEAR ) );
	}

	/**
	* Convert an optionally relative timestamp to an absolute time
	*
	* The input value will be cast to an integer and interpreted as follows:
	* - zero: no expiry; return zero (e.g. TTL_INDEFINITE)
	* - negative: relative TTL; return UNIX timestamp offset by this value
	* - positive (< 10 years): relative TTL; return UNIX timestamp offset by this value
	* - positive (>= 10 years): absolute UNIX timestamp; return this value
	*
	* @param int $exptime
	*
	* @return int Expiration timestamp or TTL_INDEFINITE for indefinite
	* @since 1.34
	*/
	final protected function getExpirationAsTimestamp( $exptime ) {
	if ( $exptime == self::TTL_INDEFINITE ) {
	return $exptime;
	}

	return $this->isRelativeExpiration( $exptime )
	? intval( $this->getCurrentTime() + $exptime )
	: $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.
	*
	* The input value will be cast to an integer and interpreted as follows:
	* - zero: no expiry; return zero (e.g. TTL_INDEFINITE)
	* - negative: relative TTL; return a short expiry time (1 second)
	* - positive (< 10 years): relative TTL; return this value
	* - positive (>= 10 years): absolute UNIX timestamp; return offset to current time
	*
	* @param int $exptime
	*
	* @return int Relative TTL or TTL_INDEFINITE for indefinite
	* @since 1.34
	*/
	final protected function getExpirationAsTTL( $exptime ) {
	if ( $exptime == self::TTL_INDEFINITE ) {
	return $exptime;
	}

	return $this->isRelativeExpiration( $exptime )
	? $exptime
	: (int)max( $exptime - $this->getCurrentTime(), 1 );
	}

	/**
	* Check if a value is an integer
	*
	* @param mixed $value
	*
	* @return bool
	*/
	final protected function isInteger( $value ) {
	if ( is_int( $value ) ) {
	return true;
	} elseif ( !is_string( $value ) ) {
	return false;
	}

	$integer = (int)$value;

	return ( $value === (string)$integer );
	}

	/** @inheritDoc */
	public function getQoS( $flag ) {
	return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
	}

	/**
	* @deprecated since 1.43, not used anywhere.
	*/
	public function getSegmentationSize() {
	wfDeprecated( __METHOD__, '1.43' );

	return $this->segmentationSize;
	}

	/**
	* @deprecated since 1.43, not used anywhere.
	*/
	public function getSegmentedValueMaxSize() {
	wfDeprecated( __METHOD__, '1.43' );

	return $this->segmentedValueMaxSize;
	}

	/**
	* Get the serialized form a value, logging a warning if it involves custom classes
	*
	* @param mixed $value
	* @param string $key
	*
	* @return string\|int String/integer representation of value
	* @since 1.35
	*/
	protected function getSerialized( $value, $key ) {
	$this->checkValueSerializability( $value, $key );

	return $this->serialize( $value );
	}

	/**
	* Log if a new cache value does not appear suitable for serialization at a quick glance
	*
	* This aids migration of values to JSON-like structures and the debugging of exceptions
	* due to serialization failure.
	*
	* This does not recurse more than one level into container structures.
	*
	* A proper cache key value is one of the following:
	* - null
	* - a scalar
	* - an array with scalar/null values
	* - an array tree with scalar/null "leaf" values
	* - an stdClass instance with scalar/null field values
	* - an stdClass instance tree with scalar/null "leaf" values
	* - an instance of a class that implements JsonSerializable
	*
	* @param mixed $value Result of the value generation callback for the key
	* @param string $key Cache key
	*/
	private function checkValueSerializability( $value, $key ) {
	if ( is_array( $value ) ) {
	$this->checkIterableMapSerializability( $value, $key );
	} elseif ( is_object( $value ) ) {
	// Note that Closure instances count as objects
	if ( $value instanceof stdClass ) {
	$this->checkIterableMapSerializability( $value, $key );
	} elseif ( !( $value instanceof JsonSerializable ) ) {
	$this->logger->warning(
	"{class} value for '{cachekey}'; serialization is suspect.",
	[ 'cachekey' => $key, 'class' => get_class( $value ) ]
	);
	}
	}
	}

	/**
	* @param array\|stdClass $value Result of the value generation callback for the key
	* @param string $key Cache key
	*/
	private function checkIterableMapSerializability( $value, $key ) {
	foreach ( $value as $index => $entry ) {
	if ( is_object( $entry ) ) {
	// Note that Closure instances count as objects
	if (
	!( $entry instanceof \stdClass ) &&
	!( $entry instanceof \JsonSerializable )
	) {
	$this->logger->warning(
	"{class} value for '{cachekey}' at '$index'; serialization is suspect.",
	[ 'cachekey' => $key, 'class' => get_class( $entry ) ]
	);

	return;
	}
	}
	}
	}

	/**
	* @param mixed $value
	*
	* @return string\|int\|false String/integer representation
	* @note Special handling is usually needed for integers so incr()/decr() work
	*/
	protected function serialize( $value ) {
	return is_int( $value ) ? $value : serialize( $value );
	}

	/**
	* @param string\|int\|false $value
	*
	* @return mixed Original value or false on error
	* @note Special handling is usually needed for integers so incr()/decr() work
	*/
	protected function unserialize( $value ) {
	return $this->isInteger( $value ) ? (int)$value : unserialize( $value );
	}

	/**
	* @param string $text
	*/
	protected function debug( $text ) {
	$this->logger->debug( "{class} debug: $text", [ 'class' => static::class ] );
	}

	/**
	* @param string $key Key generated by BagOStuff::makeKeyInternal
	*
	* @return string A stats prefix to describe this class of key (e.g. "objectcache.file")
	*/
	private function determinekeyGroupForStats( $key ): string {
	// Key came directly from BagOStuff::makeKey() or BagOStuff::makeGlobalKey()
	// and thus has the format of "<scope>:<collection>[:<constant or variable>]..."
	$components = explode( ':', $key, 3 );
	// Handle legacy callers that fail to use the key building methods
	$keygroup = $components[1] ?? 'UNKNOWN';

	return strtr( $keygroup, '.', '_' );
	}

	/**
	* @param string $op Operation name as a MediumSpecificBagOStuff::METRIC_OP_* constant
	* @param array<int,string>\|array<string,int[]> $keyInfo Key list, if payload sizes are not
	* applicable, otherwise, map of (key => (send payload size, receive payload size)); send
	* and receive sizes are 0 where not applicable and receive sizes are "false" for keys
	* that were not found during read operations
	*/
	protected function updateOpStats( string $op, array $keyInfo ) {
	$deltasByMetric = [];

	foreach ( $keyInfo as $indexOrKey => $keyOrSizes ) {
	if ( is_array( $keyOrSizes ) ) {
	$key = $indexOrKey;
	[ $sPayloadSize, $rPayloadSize ] = $keyOrSizes;
	} else {
	$key = $keyOrSizes;
	$sPayloadSize = 0;
	$rPayloadSize = 0;
	}

	// Metric prefix for the cache wrapper and key collection name
	$keygroup = $this->determinekeyGroupForStats( $key );

	if ( $op === self::METRIC_OP_GET ) {
	// This operation was either a "hit" or "miss" for this key
	if ( $rPayloadSize === false ) {
	$statsName = "bagostuff_miss_total";
	} else {
	$statsName = "bagostuff_hit_total";
	}
	} else {
	// There is no concept of "hit" or "miss" for this operation
	$statsName = "bagostuff_call_total";
	}
	$deltasByMetric[$statsName][$keygroup] = ( $deltasByMetric[$statsName][$keygroup] ?? 0 ) + 1;

	if ( $sPayloadSize > 0 ) {
	$statsName = "bagostuff_bytes_sent_total";
	$deltasByMetric[$statsName][$keygroup] =
	( $deltasByMetric[$statsName][$keygroup] ?? 0 ) + $sPayloadSize;
	}

	if ( $rPayloadSize > 0 ) {
	$statsName = "bagostuff_bytes_read_total";
	$deltasByMetric[$statsName][$keygroup] =
	( $deltasByMetric[$statsName][$keygroup] ?? 0 ) + $rPayloadSize;
	}
	}

	foreach ( $deltasByMetric as $statsName => $deltaByKeygroup ) {
	$stats = $this->stats->getCounter( $statsName );
	foreach ( $deltaByKeygroup as $keygroup => $delta ) {
	$stats->setLabel( 'keygroup', $keygroup )
	->setLabel( 'operation', $op )
	->incrementBy( $delta );
	}
	}
	}
	}

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

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