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 callable|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 /** Bitfield constants for get()/getMulti() */
91 const READ_LATEST
= 1; // use latest data for replicated stores
92 const READ_VERIFIED
= 2; // promise that caller can tell when keys are stale
93 /** Bitfield constants for set()/merge() */
94 const WRITE_SYNC
= 1; // synchronously write to all locations for replicated stores
95 const WRITE_CACHE_ONLY
= 2; // Only change state of the in-memory cache
99 * - logger: Psr\Log\LoggerInterface instance
100 * - keyspace: Default keyspace for $this->makeKey()
101 * - asyncHandler: Callable to use for scheduling tasks after the web request ends.
102 * In CLI mode, it should run the task immediately.
103 * - reportDupes: Whether to emit warning log messages for all keys that were
104 * requested more than once (requires an asyncHandler).
105 * - syncTimeout: How long to wait with WRITE_SYNC in seconds.
106 * @param array $params
108 public function __construct( array $params = [] ) {
109 $this->setLogger( $params['logger'] ??
new NullLogger() );
111 if ( isset( $params['keyspace'] ) ) {
112 $this->keyspace
= $params['keyspace'];
115 $this->asyncHandler
= $params['asyncHandler'] ??
null;
117 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler
) ) {
118 $this->reportDupes
= true;
121 $this->syncTimeout
= $params['syncTimeout'] ??
3;
125 * @param LoggerInterface $logger
128 public function setLogger( LoggerInterface
$logger ) {
129 $this->logger
= $logger;
135 public function setDebug( $bool ) {
136 $this->debugMode
= $bool;
140 * Get an item with the given key, regenerating and setting it if not found
142 * If the callback returns false, then nothing is stored.
145 * @param int $ttl Time-to-live (seconds)
146 * @param callable $callback Callback that derives the new value
147 * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
148 * @return mixed The cached value if found or the result of $callback otherwise
151 final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
152 $value = $this->get( $key, $flags );
154 if ( $value === false ) {
155 if ( !is_callable( $callback ) ) {
156 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
158 $value = call_user_func( $callback );
159 if ( $value !== false ) {
160 $this->set( $key, $value, $ttl );
168 * Get an item with the given key
170 * If the key includes a deterministic input hash (e.g. the key can only have
171 * the correct value) or complete staleness checks are handled by the caller
172 * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
173 * This lets tiered backends know they can safely upgrade a cached value to
174 * higher tiers using standard TTLs.
177 * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
178 * @param int|null $oldFlags [unused]
179 * @return mixed Returns false on failure and if the item does not exist
181 public function get( $key, $flags = 0, $oldFlags = null ) {
182 // B/C for ( $key, &$casToken = null, $flags = 0 )
183 $flags = is_int( $oldFlags ) ?
$oldFlags : $flags;
185 $this->trackDuplicateKeys( $key );
187 return $this->doGet( $key, $flags );
191 * Track the number of times that a given key has been used.
194 private function trackDuplicateKeys( $key ) {
195 if ( !$this->reportDupes
) {
199 if ( !isset( $this->duplicateKeyLookups
[$key] ) ) {
200 // Track that we have seen this key. This N-1 counting style allows
201 // easy filtering with array_filter() later.
202 $this->duplicateKeyLookups
[$key] = 0;
204 $this->duplicateKeyLookups
[$key] +
= 1;
206 if ( $this->dupeTrackScheduled
=== false ) {
207 $this->dupeTrackScheduled
= true;
208 // Schedule a callback that logs keys processed more than once by get().
209 call_user_func( $this->asyncHandler
, function () {
210 $dups = array_filter( $this->duplicateKeyLookups
);
211 foreach ( $dups as $key => $count ) {
212 $this->logger
->warning(
213 'Duplicate get(): "{key}" fetched {count} times',
214 // Count is N-1 of the actual lookup count
215 [ 'key' => $key, 'count' => $count +
1, ]
225 * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
226 * @return mixed Returns false on failure and if the item does not exist
228 abstract protected function doGet( $key, $flags = 0 );
231 * @note This method is only needed if merge() uses mergeViaCas()
234 * @param mixed &$casToken
235 * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
236 * @return mixed Returns false on failure and if the item does not exist
239 protected function getWithToken( $key, &$casToken, $flags = 0 ) {
240 throw new Exception( __METHOD__
. ' not implemented.' );
247 * @param mixed $value
248 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
249 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
250 * @return bool Success
252 abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
258 * @return bool True if the item was deleted or not found, false on failure
259 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
261 abstract public function delete( $key, $flags = 0 );
264 * Merge changes into the existing cache value (possibly creating a new one)
266 * The callback function returns the new value given the current value
267 * (which will be false if not present), and takes the arguments:
268 * (this BagOStuff, cache key, current value, TTL).
269 * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
272 * @param callable $callback Callback method to be executed
273 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
274 * @param int $attempts The amount of times to attempt a merge in case of failure
275 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
276 * @return bool Success
277 * @throws InvalidArgumentException
279 public function merge( $key, callable
$callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
280 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
284 * @see BagOStuff::merge()
287 * @param callable $callback Callback method to be executed
288 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
289 * @param int $attempts The amount of times to attempt a merge in case of failure
290 * @return bool Success
292 protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
294 $this->clearLastError();
295 $reportDupes = $this->reportDupes
;
296 $this->reportDupes
= false;
297 $casToken = null; // passed by reference
298 $currentValue = $this->getWithToken( $key, $casToken, self
::READ_LATEST
);
299 $this->reportDupes
= $reportDupes;
301 if ( $this->getLastError() ) {
302 $this->logger
->warning(
303 __METHOD__
. ' failed due to I/O error on get() for {key}.',
307 return false; // don't spam retries (retry only on races)
310 // Derive the new value from the old value
311 $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
313 $this->clearLastError();
314 if ( $value === false ) {
315 $success = true; // do nothing
316 } elseif ( $currentValue === false ) {
317 // Try to create the key, failing if it gets created in the meantime
318 $success = $this->add( $key, $value, $exptime );
320 // Try to update the key, failing if it gets changed in the meantime
321 $success = $this->cas( $casToken, $key, $value, $exptime );
323 if ( $this->getLastError() ) {
324 $this->logger
->warning(
325 __METHOD__
. ' failed due to I/O error for {key}.',
329 return false; // IO error; don't spam retries
331 } while ( !$success && --$attempts );
337 * Check and set an item
339 * @param mixed $casToken
341 * @param mixed $value
342 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
343 * @return bool Success
346 protected function cas( $casToken, $key, $value, $exptime = 0 ) {
347 if ( !$this->lock( $key, 0 ) ) {
348 return false; // non-blocking
351 $curCasToken = null; // passed by reference
352 $this->getWithToken( $key, $curCasToken, self
::READ_LATEST
);
353 if ( $casToken === $curCasToken ) {
354 $success = $this->set( $key, $value, $exptime );
357 __METHOD__
. ' failed due to race condition for {key}.',
361 $success = false; // mismatched or failed
364 $this->unlock( $key );
370 * @see BagOStuff::merge()
373 * @param callable $callback Callback method to be executed
374 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
375 * @param int $attempts The amount of times to attempt a merge in case of failure
376 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
377 * @return bool Success
379 protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
380 if ( $attempts <= 1 ) {
381 $timeout = 0; // clearly intended to be "non-blocking"
386 if ( !$this->lock( $key, $timeout ) ) {
390 $this->clearLastError();
391 $reportDupes = $this->reportDupes
;
392 $this->reportDupes
= false;
393 $currentValue = $this->get( $key, self
::READ_LATEST
);
394 $this->reportDupes
= $reportDupes;
396 if ( $this->getLastError() ) {
397 $this->logger
->warning(
398 __METHOD__
. ' failed due to I/O error on get() for {key}.',
404 // Derive the new value from the old value
405 $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
406 if ( $value === false ) {
407 $success = true; // do nothing
409 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
413 if ( !$this->unlock( $key ) ) {
414 // this should never happen
415 trigger_error( "Could not release lock for key '$key'." );
422 * Reset the TTL on a key if it exists
426 * @return bool Success Returns false if there is no key
429 public function changeTTL( $key, $expiry = 0 ) {
430 $value = $this->get( $key );
432 return ( $value === false ) ?
false : $this->set( $key, $value, $expiry );
436 * Acquire an advisory lock on a key string
438 * Note that if reentry is enabled, duplicate calls ignore $expiry
441 * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
442 * @param int $expiry Lock expiry [optional]; 1 day maximum
443 * @param string $rclass Allow reentry if set and the current lock used this value
444 * @return bool Success
446 public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
447 // Avoid deadlocks and allow lock reentry if specified
448 if ( isset( $this->locks
[$key] ) ) {
449 if ( $rclass != '' && $this->locks
[$key]['class'] === $rclass ) {
450 ++
$this->locks
[$key]['depth'];
458 $expiry = min( $expiry ?
: INF
, self
::TTL_DAY
);
459 $loop = new WaitConditionLoop(
460 function () use ( $key, $expiry, $fname ) {
461 $this->clearLastError();
462 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
463 return true; // locked!
464 } elseif ( $this->getLastError() ) {
465 $this->logger
->warning(
466 $fname . ' failed due to I/O error for {key}.',
470 return WaitConditionLoop
::CONDITION_ABORTED
; // network partition?
473 return WaitConditionLoop
::CONDITION_CONTINUE
;
478 $code = $loop->invoke();
479 $locked = ( $code === $loop::CONDITION_REACHED
);
481 $this->locks
[$key] = [ 'class' => $rclass, 'depth' => 1 ];
482 } elseif ( $code === $loop::CONDITION_TIMED_OUT
) {
483 $this->logger
->warning(
484 "$fname failed due to timeout for {key}.",
485 [ 'key' => $key, 'timeout' => $timeout ]
493 * Release an advisory lock on a key string
496 * @return bool Success
498 public function unlock( $key ) {
499 if ( isset( $this->locks
[$key] ) && --$this->locks
[$key]['depth'] <= 0 ) {
500 unset( $this->locks
[$key] );
502 $ok = $this->delete( "{$key}:lock" );
504 $this->logger
->warning(
505 __METHOD__
. ' failed to release lock for {key}.',
517 * Get a lightweight exclusive self-unlocking lock
519 * Note that the same lock cannot be acquired twice.
521 * This is useful for task de-duplication or to avoid obtrusive
522 * (though non-corrupting) DB errors like INSERT key conflicts
523 * or deadlocks when using LOCK IN SHARE MODE.
526 * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
527 * @param int $expiry Lock expiry [optional]; 1 day maximum
528 * @param string $rclass Allow reentry if set and the current lock used this value
529 * @return ScopedCallback|null Returns null on failure
532 final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
533 $expiry = min( $expiry ?
: INF
, self
::TTL_DAY
);
535 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
539 $lSince = $this->getCurrentTime(); // lock timestamp
541 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
542 $latency = 0.050; // latency skew (err towards keeping lock present)
543 $age = ( $this->getCurrentTime() - $lSince +
$latency );
544 if ( ( $age +
$latency ) >= $expiry ) {
545 $this->logger
->warning(
546 "Lock for {key} held too long ({age} sec).",
547 [ 'key' => $key, 'age' => $age ]
549 return; // expired; it's not "safe" to delete the key
551 $this->unlock( $key );
556 * Delete all objects expiring before a certain date.
557 * @param string $date The reference date in MW format
558 * @param callable|bool $progressCallback Optional, a function which will be called
559 * regularly during long-running operations with the percentage progress
560 * as the first parameter.
562 * @return bool Success, false if unimplemented
564 public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
570 * Get an associative array containing the item for each of the keys that have items.
571 * @param array $keys List of strings
572 * @param int $flags Bitfield; supports READ_LATEST [optional]
575 public function getMulti( array $keys, $flags = 0 ) {
577 foreach ( $keys as $key ) {
578 $val = $this->get( $key );
579 if ( $val !== false ) {
588 * @param array $data $key => $value assoc array
589 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
590 * @return bool Success
593 public function setMulti( array $data, $exptime = 0 ) {
595 foreach ( $data as $key => $value ) {
596 if ( !$this->set( $key, $value, $exptime ) ) {
605 * @param mixed $value
606 * @param int $exptime
607 * @return bool Success
609 public function add( $key, $value, $exptime = 0 ) {
610 // @note: avoid lock() here since that method uses *this* method by default
611 if ( $this->get( $key ) === false ) {
612 return $this->set( $key, $value, $exptime );
614 return false; // key already set
618 * Increase stored value of $key by $value while preserving its TTL
619 * @param string $key Key to increase
620 * @param int $value Value to add to $key (Default 1)
621 * @return int|bool New value or false on failure
623 public function incr( $key, $value = 1 ) {
624 if ( !$this->lock( $key, 1 ) ) {
627 $n = $this->get( $key );
628 if ( $this->isInteger( $n ) ) { // key exists?
629 $n +
= intval( $value );
630 $this->set( $key, max( 0, $n ) ); // exptime?
634 $this->unlock( $key );
640 * Decrease stored value of $key by $value while preserving its TTL
643 * @return int|bool New value or false on failure
645 public function decr( $key, $value = 1 ) {
646 return $this->incr( $key, - $value );
650 * Increase stored value of $key by $value while preserving its TTL
652 * This will create the key with value $init and TTL $ttl instead if not present
658 * @return int|bool New value or false on failure
661 public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
662 $this->clearLastError();
663 $newValue = $this->incr( $key, $value );
664 if ( $newValue === false && !$this->getLastError() ) {
665 // No key set; initialize
666 $newValue = $this->add( $key, (int)$init, $ttl ) ?
$init : false;
667 if ( $newValue === false && !$this->getLastError() ) {
668 // Raced out initializing; increment
669 $newValue = $this->incr( $key, $value );
677 * Get the "last error" registered; clearLastError() should be called manually
678 * @return int ERR_* constant for the "last error" registry
681 public function getLastError() {
682 return $this->lastError
;
686 * Clear the "last error" registry
689 public function clearLastError() {
690 $this->lastError
= self
::ERR_NONE
;
694 * Set the "last error" registry
695 * @param int $err ERR_* constant
698 protected function setLastError( $err ) {
699 $this->lastError
= $err;
703 * Let a callback be run to avoid wasting time on special blocking calls
705 * The callbacks may or may not be called ever, in any particular order.
706 * They are likely to be invoked when something WRITE_SYNC is used used.
707 * They should follow a caching pattern as shown below, so that any code
708 * using the work will get it's result no matter what happens.
711 * $workCallback = function () use ( &$result ) {
719 * @param callable $workCallback
722 public function addBusyCallback( callable
$workCallback ) {
723 $this->busyCallbacks
[] = $workCallback;
727 * Modify a cache update operation array for EventRelayer::notify()
729 * This is used for relayed writes, e.g. for broadcasting a change
730 * to multiple data-centers. If the array contains a 'val' field
731 * then the command involves setting a key to that value. Note that
732 * for simplicity, 'val' is always a simple scalar value. This method
733 * is used to possibly serialize the value and add any cache-specific
734 * key/values needed for the relayer daemon (e.g. memcached flags).
736 * @param array $event
740 public function modifySimpleRelayEvent( array $event ) {
745 * @param string $text
747 protected function debug( $text ) {
748 if ( $this->debugMode
) {
749 $this->logger
->debug( "{class} debug: $text", [
750 'class' => static::class,
756 * Convert an optionally relative time to an absolute time
757 * @param int $exptime
760 protected function convertExpiry( $exptime ) {
761 if ( $exptime != 0 && $exptime < ( 10 * self
::TTL_YEAR
) ) {
762 return (int)$this->getCurrentTime() +
$exptime;
769 * Convert an optionally absolute expiry time to a relative time. If an
770 * absolute time is specified which is in the past, use a short expiry time.
772 * @param int $exptime
775 protected function convertToRelative( $exptime ) {
776 if ( $exptime >= ( 10 * self
::TTL_YEAR
) ) {
777 $exptime -= (int)$this->getCurrentTime();
778 if ( $exptime <= 0 ) {
788 * Check if a value is an integer
790 * @param mixed $value
793 protected function isInteger( $value ) {
794 return ( is_int( $value ) ||
ctype_digit( $value ) );
798 * Construct a cache key.
801 * @param string $keyspace
803 * @return string Colon-delimited list of $keyspace followed by escaped components of $args
805 public function makeKeyInternal( $keyspace, $args ) {
807 foreach ( $args as $arg ) {
808 $arg = str_replace( ':', '%3A', $arg );
811 return strtr( $key, ' ', '_' );
815 * Make a global cache key.
818 * @param string $class Key class
819 * @param string|null $component [optional] Key component (starting with a key collection name)
820 * @return string Colon-delimited list of $keyspace followed by escaped components of $args
822 public function makeGlobalKey( $class, $component = null ) {
823 return $this->makeKeyInternal( 'global', func_get_args() );
827 * Make a cache key, scoped to this instance's keyspace.
830 * @param string $class Key class
831 * @param string|null $component [optional] Key component (starting with a key collection name)
832 * @return string Colon-delimited list of $keyspace followed by escaped components of $args
834 public function makeKey( $class, $component = null ) {
835 return $this->makeKeyInternal( $this->keyspace
, func_get_args() );
839 * @param int $flag ATTR_* class constant
840 * @return int QOS_* class constant
843 public function getQoS( $flag ) {
844 return $this->attrMap
[$flag] ?? self
::QOS_UNKNOWN
;
848 * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
850 * @param BagOStuff[] $bags
851 * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
853 protected function mergeFlagMaps( array $bags ) {
855 foreach ( $bags as $bag ) {
856 foreach ( $bag->attrMap
as $attr => $rank ) {
857 if ( isset( $map[$attr] ) ) {
858 $map[$attr] = min( $map[$attr], $rank );
869 * @return float UNIX timestamp
870 * @codeCoverageIgnore
872 protected function getCurrentTime() {
873 return $this->wallClockOverride ?
: microtime( true );
877 * @param float|null &$time Mock UNIX timestamp for testing
878 * @codeCoverageIgnore
880 public function setMockTime( &$time ) {
881 $this->wallClockOverride
=& $time;