3 * Copyright © 2003-2004 Brion Vibber <brion@pobox.com>
4 * https://www.mediawiki.org/
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License along
17 * with this program; if not, write to the Free Software Foundation, Inc.,
18 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
19 * http://www.gnu.org/copyleft/gpl.html
26 * @defgroup Cache Cache
29 use Psr\Log\LoggerAwareInterface
;
30 use Psr\Log\LoggerInterface
;
31 use Psr\Log\NullLogger
;
32 use Wikimedia\ScopedCallback
;
33 use Wikimedia\WaitConditionLoop
;
36 * Class representing a cache/ephemeral data store
38 * This interface is intended to be more or less compatible with the PHP memcached client.
40 * Instances of this class should be created with an intended access scope, such as:
41 * - a) A single PHP thread on a server (e.g. stored in a PHP variable)
42 * - b) A single application server (e.g. stored in APC or sqlite)
43 * - c) All application servers in datacenter (e.g. stored in memcached or mysql)
44 * - d) All application servers in all datacenters (e.g. stored via mcrouter or dynomite)
46 * Callers should use the proper factory methods that yield BagOStuff instances. Site admins
47 * should make sure the configuration for those factory methods matches their access scope.
48 * BagOStuff subclasses have widely varying levels of support for replication features.
50 * For any given instance, methods like lock(), unlock(), merge(), and set() with WRITE_SYNC
51 * should semantically operate over its entire access scope; any nodes/threads in that scope
52 * should serialize appropriately when using them. Likewise, a call to get() with READ_LATEST
53 * from one node in its access scope should reflect the prior changes of any other node its access
54 * scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.
58 abstract class BagOStuff
implements IExpiringStore
, LoggerAwareInterface
{
59 /** @var array[] Lock tracking */
60 protected $locks = [];
61 /** @var int ERR_* class constant */
62 protected $lastError = self
::ERR_NONE
;
64 protected $keyspace = 'local';
65 /** @var LoggerInterface */
67 /** @var callback|null */
68 protected $asyncHandler;
69 /** @var int Seconds */
70 protected $syncTimeout;
73 private $debugMode = false;
75 private $duplicateKeyLookups = [];
77 private $reportDupes = false;
79 private $dupeTrackScheduled = false;
81 /** @var callable[] */
82 protected $busyCallbacks = [];
84 /** @var float|null */
85 private $wallClockOverride;
87 /** @var int[] Map of (ATTR_* class constant => QOS_* class constant) */
88 protected $attrMap = [];
90 /** Possible values for getLastError() */
91 const ERR_NONE
= 0; // no error
92 const ERR_NO_RESPONSE
= 1; // no response
93 const ERR_UNREACHABLE
= 2; // can't connect
94 const ERR_UNEXPECTED
= 3; // response gave some error
96 /** Bitfield constants for get()/getMulti() */
97 const READ_LATEST
= 1; // use latest data for replicated stores
98 const READ_VERIFIED
= 2; // promise that caller can tell when keys are stale
99 /** Bitfield constants for set()/merge() */
100 const WRITE_SYNC
= 1; // synchronously write to all locations for replicated stores
101 const WRITE_CACHE_ONLY
= 2; // Only change state of the in-memory cache
105 * - logger: Psr\Log\LoggerInterface instance
106 * - keyspace: Default keyspace for $this->makeKey()
107 * - asyncHandler: Callable to use for scheduling tasks after the web request ends.
108 * In CLI mode, it should run the task immediately.
109 * - reportDupes: Whether to emit warning log messages for all keys that were
110 * requested more than once (requires an asyncHandler).
111 * - syncTimeout: How long to wait with WRITE_SYNC in seconds.
112 * @param array $params
114 public function __construct( array $params = [] ) {
115 if ( isset( $params['logger'] ) ) {
116 $this->setLogger( $params['logger'] );
118 $this->setLogger( new NullLogger() );
121 if ( isset( $params['keyspace'] ) ) {
122 $this->keyspace
= $params['keyspace'];
125 $this->asyncHandler
= $params['asyncHandler'] ??
null;
127 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler
) ) {
128 $this->reportDupes
= true;
131 $this->syncTimeout
= $params['syncTimeout'] ??
3;
135 * @param LoggerInterface $logger
138 public function setLogger( LoggerInterface
$logger ) {
139 $this->logger
= $logger;
145 public function setDebug( $bool ) {
146 $this->debugMode
= $bool;
150 * Get an item with the given key, regenerating and setting it if not found
152 * If the callback returns false, then nothing is stored.
155 * @param int $ttl Time-to-live (seconds)
156 * @param callable $callback Callback that derives the new value
157 * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
158 * @return mixed The cached value if found or the result of $callback otherwise
161 final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
162 $value = $this->get( $key, $flags );
164 if ( $value === false ) {
165 if ( !is_callable( $callback ) ) {
166 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
168 $value = call_user_func( $callback );
169 if ( $value !== false ) {
170 $this->set( $key, $value, $ttl );
178 * Get an item with the given key
180 * If the key includes a deterministic input hash (e.g. the key can only have
181 * the correct value) or complete staleness checks are handled by the caller
182 * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
183 * This lets tiered backends know they can safely upgrade a cached value to
184 * higher tiers using standard TTLs.
187 * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
188 * @param int|null $oldFlags [unused]
189 * @return mixed Returns false on failure and if the item does not exist
191 public function get( $key, $flags = 0, $oldFlags = null ) {
192 // B/C for ( $key, &$casToken = null, $flags = 0 )
193 $flags = is_int( $oldFlags ) ?
$oldFlags : $flags;
195 $this->trackDuplicateKeys( $key );
197 return $this->doGet( $key, $flags );
201 * Track the number of times that a given key has been used.
204 private function trackDuplicateKeys( $key ) {
205 if ( !$this->reportDupes
) {
209 if ( !isset( $this->duplicateKeyLookups
[$key] ) ) {
210 // Track that we have seen this key. This N-1 counting style allows
211 // easy filtering with array_filter() later.
212 $this->duplicateKeyLookups
[$key] = 0;
214 $this->duplicateKeyLookups
[$key] +
= 1;
216 if ( $this->dupeTrackScheduled
=== false ) {
217 $this->dupeTrackScheduled
= true;
218 // Schedule a callback that logs keys processed more than once by get().
219 call_user_func( $this->asyncHandler
, function () {
220 $dups = array_filter( $this->duplicateKeyLookups
);
221 foreach ( $dups as $key => $count ) {
222 $this->logger
->warning(
223 'Duplicate get(): "{key}" fetched {count} times',
224 // Count is N-1 of the actual lookup count
225 [ 'key' => $key, 'count' => $count +
1, ]
235 * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
236 * @return mixed Returns false on failure and if the item does not exist
238 abstract protected function doGet( $key, $flags = 0 );
241 * @note: This method is only needed if merge() uses mergeViaCas()
244 * @param mixed &$casToken
245 * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
246 * @return mixed Returns false on failure and if the item does not exist
249 protected function getWithToken( $key, &$casToken, $flags = 0 ) {
250 throw new Exception( __METHOD__
. ' not implemented.' );
257 * @param mixed $value
258 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
259 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
260 * @return bool Success
262 abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
268 * @return bool True if the item was deleted or not found, false on failure
270 abstract public function delete( $key );
273 * Merge changes into the existing cache value (possibly creating a new one)
275 * The callback function returns the new value given the current value
276 * (which will be false if not present), and takes the arguments:
277 * (this BagOStuff, cache key, current value, TTL).
278 * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
281 * @param callable $callback Callback method to be executed
282 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
283 * @param int $attempts The amount of times to attempt a merge in case of failure
284 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
285 * @return bool Success
286 * @throws InvalidArgumentException
288 public function merge( $key, callable
$callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
289 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
293 * @see BagOStuff::merge()
296 * @param callable $callback Callback method to be executed
297 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
298 * @param int $attempts The amount of times to attempt a merge in case of failure
299 * @return bool Success
301 protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
303 $this->clearLastError();
304 $reportDupes = $this->reportDupes
;
305 $this->reportDupes
= false;
306 $casToken = null; // passed by reference
307 $currentValue = $this->getWithToken( $key, $casToken, self
::READ_LATEST
);
308 $this->reportDupes
= $reportDupes;
310 if ( $this->getLastError() ) {
311 $this->logger
->warning(
312 __METHOD__
. ' failed due to I/O error on get() for {key}.',
316 return false; // don't spam retries (retry only on races)
319 // Derive the new value from the old value
320 $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
322 $this->clearLastError();
323 if ( $value === false ) {
324 $success = true; // do nothing
325 } elseif ( $currentValue === false ) {
326 // Try to create the key, failing if it gets created in the meantime
327 $success = $this->add( $key, $value, $exptime );
329 // Try to update the key, failing if it gets changed in the meantime
330 $success = $this->cas( $casToken, $key, $value, $exptime );
332 if ( $this->getLastError() ) {
333 $this->logger
->warning(
334 __METHOD__
. ' failed due to I/O error for {key}.',
338 return false; // IO error; don't spam retries
340 } while ( !$success && --$attempts );
346 * Check and set an item
348 * @param mixed $casToken
350 * @param mixed $value
351 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
352 * @return bool Success
355 protected function cas( $casToken, $key, $value, $exptime = 0 ) {
356 if ( !$this->lock( $key, 0 ) ) {
357 return false; // non-blocking
360 $curCasToken = null; // passed by reference
361 $this->getWithToken( $key, $curCasToken, self
::READ_LATEST
);
362 if ( $casToken === $curCasToken ) {
363 $success = $this->set( $key, $value, $exptime );
366 __METHOD__
. ' failed due to race condition for {key}.',
370 $success = false; // mismatched or failed
373 $this->unlock( $key );
379 * @see BagOStuff::merge()
382 * @param callable $callback Callback method to be executed
383 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
384 * @param int $attempts The amount of times to attempt a merge in case of failure
385 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
386 * @return bool Success
388 protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
389 if ( $attempts <= 1 ) {
390 $timeout = 0; // clearly intended to be "non-blocking"
395 if ( !$this->lock( $key, $timeout ) ) {
399 $this->clearLastError();
400 $reportDupes = $this->reportDupes
;
401 $this->reportDupes
= false;
402 $currentValue = $this->get( $key, self
::READ_LATEST
);
403 $this->reportDupes
= $reportDupes;
405 if ( $this->getLastError() ) {
406 $this->logger
->warning(
407 __METHOD__
. ' failed due to I/O error on get() for {key}.',
413 // Derive the new value from the old value
414 $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
415 if ( $value === false ) {
416 $success = true; // do nothing
418 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
422 if ( !$this->unlock( $key ) ) {
423 // this should never happen
424 trigger_error( "Could not release lock for key '$key'." );
431 * Reset the TTL on a key if it exists
435 * @return bool Success Returns false if there is no key
438 public function changeTTL( $key, $expiry = 0 ) {
439 $value = $this->get( $key );
441 return ( $value === false ) ?
false : $this->set( $key, $value, $expiry );
445 * Acquire an advisory lock on a key string
447 * Note that if reentry is enabled, duplicate calls ignore $expiry
450 * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
451 * @param int $expiry Lock expiry [optional]; 1 day maximum
452 * @param string $rclass Allow reentry if set and the current lock used this value
453 * @return bool Success
455 public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
456 // Avoid deadlocks and allow lock reentry if specified
457 if ( isset( $this->locks
[$key] ) ) {
458 if ( $rclass != '' && $this->locks
[$key]['class'] === $rclass ) {
459 ++
$this->locks
[$key]['depth'];
467 $expiry = min( $expiry ?
: INF
, self
::TTL_DAY
);
468 $loop = new WaitConditionLoop(
469 function () use ( $key, $timeout, $expiry, $fname ) {
470 $this->clearLastError();
471 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
472 return true; // locked!
473 } elseif ( $this->getLastError() ) {
474 $this->logger
->warning(
475 $fname . ' failed due to I/O error for {key}.',
479 return WaitConditionLoop
::CONDITION_ABORTED
; // network partition?
482 return WaitConditionLoop
::CONDITION_CONTINUE
;
487 $code = $loop->invoke();
488 $locked = ( $code === $loop::CONDITION_REACHED
);
490 $this->locks
[$key] = [ 'class' => $rclass, 'depth' => 1 ];
491 } elseif ( $code === $loop::CONDITION_TIMED_OUT
) {
492 $this->logger
->warning(
493 "$fname failed due to timeout for {key}.",
494 [ 'key' => $key, 'timeout' => $timeout ]
502 * Release an advisory lock on a key string
505 * @return bool Success
507 public function unlock( $key ) {
508 if ( isset( $this->locks
[$key] ) && --$this->locks
[$key]['depth'] <= 0 ) {
509 unset( $this->locks
[$key] );
511 $ok = $this->delete( "{$key}:lock" );
513 $this->logger
->warning(
514 __METHOD__
. ' failed to release lock for {key}.',
526 * Get a lightweight exclusive self-unlocking lock
528 * Note that the same lock cannot be acquired twice.
530 * This is useful for task de-duplication or to avoid obtrusive
531 * (though non-corrupting) DB errors like INSERT key conflicts
532 * or deadlocks when using LOCK IN SHARE MODE.
535 * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
536 * @param int $expiry Lock expiry [optional]; 1 day maximum
537 * @param string $rclass Allow reentry if set and the current lock used this value
538 * @return ScopedCallback|null Returns null on failure
541 final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
542 $expiry = min( $expiry ?
: INF
, self
::TTL_DAY
);
544 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
548 $lSince = $this->getCurrentTime(); // lock timestamp
550 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
551 $latency = 0.050; // latency skew (err towards keeping lock present)
552 $age = ( $this->getCurrentTime() - $lSince +
$latency );
553 if ( ( $age +
$latency ) >= $expiry ) {
554 $this->logger
->warning(
555 "Lock for {key} held too long ({age} sec).",
556 [ 'key' => $key, 'age' => $age ]
558 return; // expired; it's not "safe" to delete the key
560 $this->unlock( $key );
565 * Delete all objects expiring before a certain date.
566 * @param string $date The reference date in MW format
567 * @param callable|bool $progressCallback Optional, a function which will be called
568 * regularly during long-running operations with the percentage progress
569 * as the first parameter.
571 * @return bool Success, false if unimplemented
573 public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
579 * Get an associative array containing the item for each of the keys that have items.
580 * @param array $keys List of strings
581 * @param int $flags Bitfield; supports READ_LATEST [optional]
584 public function getMulti( array $keys, $flags = 0 ) {
586 foreach ( $keys as $key ) {
587 $val = $this->get( $key );
588 if ( $val !== false ) {
597 * @param array $data $key => $value assoc array
598 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
599 * @return bool Success
602 public function setMulti( array $data, $exptime = 0 ) {
604 foreach ( $data as $key => $value ) {
605 if ( !$this->set( $key, $value, $exptime ) ) {
614 * @param mixed $value
615 * @param int $exptime
616 * @return bool Success
618 public function add( $key, $value, $exptime = 0 ) {
619 // @note: avoid lock() here since that method uses *this* method by default
620 if ( $this->get( $key ) === false ) {
621 return $this->set( $key, $value, $exptime );
623 return false; // key already set
627 * Increase stored value of $key by $value while preserving its TTL
628 * @param string $key Key to increase
629 * @param int $value Value to add to $key (Default 1)
630 * @return int|bool New value or false on failure
632 public function incr( $key, $value = 1 ) {
633 if ( !$this->lock( $key, 1 ) ) {
636 $n = $this->get( $key );
637 if ( $this->isInteger( $n ) ) { // key exists?
638 $n +
= intval( $value );
639 $this->set( $key, max( 0, $n ) ); // exptime?
643 $this->unlock( $key );
649 * Decrease stored value of $key by $value while preserving its TTL
652 * @return int|bool New value or false on failure
654 public function decr( $key, $value = 1 ) {
655 return $this->incr( $key, - $value );
659 * Increase stored value of $key by $value while preserving its TTL
661 * This will create the key with value $init and TTL $ttl instead if not present
667 * @return int|bool New value or false on failure
670 public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
671 $this->clearLastError();
672 $newValue = $this->incr( $key, $value );
673 if ( $newValue === false && !$this->getLastError() ) {
674 // No key set; initialize
675 $newValue = $this->add( $key, (int)$init, $ttl ) ?
$init : false;
676 if ( $newValue === false && !$this->getLastError() ) {
677 // Raced out initializing; increment
678 $newValue = $this->incr( $key, $value );
686 * Get the "last error" registered; clearLastError() should be called manually
687 * @return int ERR_* constant for the "last error" registry
690 public function getLastError() {
691 return $this->lastError
;
695 * Clear the "last error" registry
698 public function clearLastError() {
699 $this->lastError
= self
::ERR_NONE
;
703 * Set the "last error" registry
704 * @param int $err ERR_* constant
707 protected function setLastError( $err ) {
708 $this->lastError
= $err;
712 * Let a callback be run to avoid wasting time on special blocking calls
714 * The callbacks may or may not be called ever, in any particular order.
715 * They are likely to be invoked when something WRITE_SYNC is used used.
716 * They should follow a caching pattern as shown below, so that any code
717 * using the word will get it's result no matter what happens.
720 * $workCallback = function () use ( &$result ) {
728 * @param callable $workCallback
731 public function addBusyCallback( callable
$workCallback ) {
732 $this->busyCallbacks
[] = $workCallback;
736 * Modify a cache update operation array for EventRelayer::notify()
738 * This is used for relayed writes, e.g. for broadcasting a change
739 * to multiple data-centers. If the array contains a 'val' field
740 * then the command involves setting a key to that value. Note that
741 * for simplicity, 'val' is always a simple scalar value. This method
742 * is used to possibly serialize the value and add any cache-specific
743 * key/values needed for the relayer daemon (e.g. memcached flags).
745 * @param array $event
749 public function modifySimpleRelayEvent( array $event ) {
754 * @param string $text
756 protected function debug( $text ) {
757 if ( $this->debugMode
) {
758 $this->logger
->debug( "{class} debug: $text", [
759 'class' => static::class,
765 * Convert an optionally relative time to an absolute time
766 * @param int $exptime
769 protected function convertExpiry( $exptime ) {
770 if ( $exptime != 0 && $exptime < ( 10 * self
::TTL_YEAR
) ) {
771 return (int)$this->getCurrentTime() +
$exptime;
778 * Convert an optionally absolute expiry time to a relative time. If an
779 * absolute time is specified which is in the past, use a short expiry time.
781 * @param int $exptime
784 protected function convertToRelative( $exptime ) {
785 if ( $exptime >= ( 10 * self
::TTL_YEAR
) ) {
786 $exptime -= (int)$this->getCurrentTime();
787 if ( $exptime <= 0 ) {
797 * Check if a value is an integer
799 * @param mixed $value
802 protected function isInteger( $value ) {
803 return ( is_int( $value ) ||
ctype_digit( $value ) );
807 * Construct a cache key.
810 * @param string $keyspace
812 * @return string Colon-delimited list of $keyspace followed by escaped components of $args
814 public function makeKeyInternal( $keyspace, $args ) {
816 foreach ( $args as $arg ) {
817 $arg = str_replace( ':', '%3A', $arg );
818 $key = $key . ':' . $arg;
820 return strtr( $key, ' ', '_' );
824 * Make a global cache key.
827 * @param string $class Key class
828 * @param string|null $component [optional] Key component (starting with a key collection name)
829 * @return string Colon-delimited list of $keyspace followed by escaped components of $args
831 public function makeGlobalKey( $class, $component = null ) {
832 return $this->makeKeyInternal( 'global', func_get_args() );
836 * Make a cache key, scoped to this instance's keyspace.
839 * @param string $class Key class
840 * @param string|null $component [optional] Key component (starting with a key collection name)
841 * @return string Colon-delimited list of $keyspace followed by escaped components of $args
843 public function makeKey( $class, $component = null ) {
844 return $this->makeKeyInternal( $this->keyspace
, func_get_args() );
848 * @param int $flag ATTR_* class constant
849 * @return int QOS_* class constant
852 public function getQoS( $flag ) {
853 return $this->attrMap
[$flag] ?? self
::QOS_UNKNOWN
;
857 * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
859 * @param BagOStuff[] $bags
860 * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
862 protected function mergeFlagMaps( array $bags ) {
864 foreach ( $bags as $bag ) {
865 foreach ( $bag->attrMap
as $attr => $rank ) {
866 if ( isset( $map[$attr] ) ) {
867 $map[$attr] = min( $map[$attr], $rank );
878 * @return float UNIX timestamp
879 * @codeCoverageIgnore
881 protected function getCurrentTime() {
882 return $this->wallClockOverride ?
: microtime( true );
886 * @param float|null &$time Mock UNIX timestamp for testing
887 * @codeCoverageIgnore
889 public function setMockTime( &$time ) {
890 $this->wallClockOverride
=& $time;