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
;
34 * interface is intended to be more or less compatible with
35 * the PHP memcached client.
37 * backends for local hash array and SQL table included:
39 * $bag = new HashBagOStuff();
40 * $bag = new SqlBagOStuff(); # connect to db first
45 abstract class BagOStuff
implements IExpiringStore
, LoggerAwareInterface
{
46 /** @var array[] Lock tracking */
47 protected $locks = [];
48 /** @var integer ERR_* class constant */
49 protected $lastError = self
::ERR_NONE
;
51 protected $keyspace = 'local';
52 /** @var LoggerInterface */
54 /** @var callback|null */
55 protected $asyncHandler;
56 /** @var integer Seconds */
57 protected $syncTimeout;
60 private $debugMode = false;
62 private $duplicateKeyLookups = [];
64 private $reportDupes = false;
66 private $dupeTrackScheduled = false;
68 /** @var callable[] */
69 protected $busyCallbacks = [];
71 /** @var integer[] Map of (ATTR_* class constant => QOS_* class constant) */
72 protected $attrMap = [];
74 /** Possible values for getLastError() */
75 const ERR_NONE
= 0; // no error
76 const ERR_NO_RESPONSE
= 1; // no response
77 const ERR_UNREACHABLE
= 2; // can't connect
78 const ERR_UNEXPECTED
= 3; // response gave some error
80 /** Bitfield constants for get()/getMulti() */
81 const READ_LATEST
= 1; // use latest data for replicated stores
82 const READ_VERIFIED
= 2; // promise that caller can tell when keys are stale
83 /** Bitfield constants for set()/merge() */
84 const WRITE_SYNC
= 1; // synchronously write to all locations for replicated stores
85 const WRITE_CACHE_ONLY
= 2; // Only change state of the in-memory cache
89 * - logger: Psr\Log\LoggerInterface instance
90 * - keyspace: Default keyspace for $this->makeKey()
91 * - asyncHandler: Callable to use for scheduling tasks after the web request ends.
92 * In CLI mode, it should run the task immediately.
93 * - reportDupes: Whether to emit warning log messages for all keys that were
94 * requested more than once (requires an asyncHandler).
95 * - syncTimeout: How long to wait with WRITE_SYNC in seconds.
96 * @param array $params
98 public function __construct( array $params = [] ) {
99 if ( isset( $params['logger'] ) ) {
100 $this->setLogger( $params['logger'] );
102 $this->setLogger( new NullLogger() );
105 if ( isset( $params['keyspace'] ) ) {
106 $this->keyspace
= $params['keyspace'];
109 $this->asyncHandler
= isset( $params['asyncHandler'] )
110 ?
$params['asyncHandler']
113 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler
) ) {
114 $this->reportDupes
= true;
117 $this->syncTimeout
= isset( $params['syncTimeout'] ) ?
$params['syncTimeout'] : 3;
121 * @param LoggerInterface $logger
124 public function setLogger( LoggerInterface
$logger ) {
125 $this->logger
= $logger;
131 public function setDebug( $bool ) {
132 $this->debugMode
= $bool;
136 * Get an item with the given key, regenerating and setting it if not found
138 * If the callback returns false, then nothing is stored.
141 * @param int $ttl Time-to-live (seconds)
142 * @param callable $callback Callback that derives the new value
143 * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
144 * @return mixed The cached value if found or the result of $callback otherwise
147 final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
148 $value = $this->get( $key, $flags );
150 if ( $value === false ) {
151 if ( !is_callable( $callback ) ) {
152 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
154 $value = call_user_func( $callback );
155 if ( $value !== false ) {
156 $this->set( $key, $value, $ttl );
164 * Get an item with the given key
166 * If the key includes a determistic input hash (e.g. the key can only have
167 * the correct value) or complete staleness checks are handled by the caller
168 * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
169 * This lets tiered backends know they can safely upgrade a cached value to
170 * higher tiers using standard TTLs.
173 * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
174 * @param integer $oldFlags [unused]
175 * @return mixed Returns false on failure and if the item does not exist
177 public function get( $key, $flags = 0, $oldFlags = null ) {
178 // B/C for ( $key, &$casToken = null, $flags = 0 )
179 $flags = is_int( $oldFlags ) ?
$oldFlags : $flags;
181 $this->trackDuplicateKeys( $key );
183 return $this->doGet( $key, $flags );
187 * Track the number of times that a given key has been used.
190 private function trackDuplicateKeys( $key ) {
191 if ( !$this->reportDupes
) {
195 if ( !isset( $this->duplicateKeyLookups
[$key] ) ) {
196 // Track that we have seen this key. This N-1 counting style allows
197 // easy filtering with array_filter() later.
198 $this->duplicateKeyLookups
[$key] = 0;
200 $this->duplicateKeyLookups
[$key] +
= 1;
202 if ( $this->dupeTrackScheduled
=== false ) {
203 $this->dupeTrackScheduled
= true;
204 // Schedule a callback that logs keys processed more than once by get().
205 call_user_func( $this->asyncHandler
, function () {
206 $dups = array_filter( $this->duplicateKeyLookups
);
207 foreach ( $dups as $key => $count ) {
208 $this->logger
->warning(
209 'Duplicate get(): "{key}" fetched {count} times',
210 // Count is N-1 of the actual lookup count
211 [ 'key' => $key, 'count' => $count +
1, ]
221 * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
222 * @return mixed Returns false on failure and if the item does not exist
224 abstract protected function doGet( $key, $flags = 0 );
227 * @note: This method is only needed if merge() uses mergeViaCas()
230 * @param mixed $casToken
231 * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
232 * @return mixed Returns false on failure and if the item does not exist
235 protected function getWithToken( $key, &$casToken, $flags = 0 ) {
236 throw new Exception( __METHOD__
. ' not implemented.' );
243 * @param mixed $value
244 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
245 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
246 * @return bool Success
248 abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
254 * @return bool True if the item was deleted or not found, false on failure
256 abstract public function delete( $key );
259 * Merge changes into the existing cache value (possibly creating a new one)
261 * The callback function returns the new value given the current value
262 * (which will be false if not present), and takes the arguments:
263 * (this BagOStuff, cache key, current value, TTL).
264 * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
267 * @param callable $callback Callback method to be executed
268 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
269 * @param int $attempts The amount of times to attempt a merge in case of failure
270 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
271 * @return bool Success
272 * @throws InvalidArgumentException
274 public function merge( $key, callable
$callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
275 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
279 * @see BagOStuff::merge()
282 * @param callable $callback Callback method to be executed
283 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
284 * @param int $attempts The amount of times to attempt a merge in case of failure
285 * @return bool Success
287 protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
289 $this->clearLastError();
290 $reportDupes = $this->reportDupes
;
291 $this->reportDupes
= false;
292 $casToken = null; // passed by reference
293 $currentValue = $this->getWithToken( $key, $casToken, self
::READ_LATEST
);
294 $this->reportDupes
= $reportDupes;
296 if ( $this->getLastError() ) {
297 return false; // don't spam retries (retry only on races)
300 // Derive the new value from the old value
301 $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
303 $this->clearLastError();
304 if ( $value === false ) {
305 $success = true; // do nothing
306 } elseif ( $currentValue === false ) {
307 // Try to create the key, failing if it gets created in the meantime
308 $success = $this->add( $key, $value, $exptime );
310 // Try to update the key, failing if it gets changed in the meantime
311 $success = $this->cas( $casToken, $key, $value, $exptime );
313 if ( $this->getLastError() ) {
314 return false; // IO error; don't spam retries
316 } while ( !$success && --$attempts );
322 * Check and set an item
324 * @param mixed $casToken
326 * @param mixed $value
327 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
328 * @return bool Success
331 protected function cas( $casToken, $key, $value, $exptime = 0 ) {
332 throw new Exception( "CAS is not implemented in " . __CLASS__
);
336 * @see BagOStuff::merge()
339 * @param callable $callback Callback method to be executed
340 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
341 * @param int $attempts The amount of times to attempt a merge in case of failure
342 * @param int $flags Bitfield of BagOStuff::WRITE_* constants
343 * @return bool Success
345 protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
346 if ( !$this->lock( $key, 6 ) ) {
350 $this->clearLastError();
351 $reportDupes = $this->reportDupes
;
352 $this->reportDupes
= false;
353 $currentValue = $this->get( $key, self
::READ_LATEST
);
354 $this->reportDupes
= $reportDupes;
356 if ( $this->getLastError() ) {
359 // Derive the new value from the old value
360 $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
361 if ( $value === false ) {
362 $success = true; // do nothing
364 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
368 if ( !$this->unlock( $key ) ) {
369 // this should never happen
370 trigger_error( "Could not release lock for key '$key'." );
377 * Reset the TTL on a key if it exists
381 * @return bool Success Returns false if there is no key
384 public function changeTTL( $key, $expiry = 0 ) {
385 $value = $this->get( $key );
387 return ( $value === false ) ?
false : $this->set( $key, $value, $expiry );
391 * Acquire an advisory lock on a key string
393 * Note that if reentry is enabled, duplicate calls ignore $expiry
396 * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
397 * @param int $expiry Lock expiry [optional]; 1 day maximum
398 * @param string $rclass Allow reentry if set and the current lock used this value
399 * @return bool Success
401 public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
402 // Avoid deadlocks and allow lock reentry if specified
403 if ( isset( $this->locks
[$key] ) ) {
404 if ( $rclass != '' && $this->locks
[$key]['class'] === $rclass ) {
405 ++
$this->locks
[$key]['depth'];
412 $expiry = min( $expiry ?
: INF
, self
::TTL_DAY
);
414 $this->clearLastError();
415 $timestamp = microtime( true ); // starting UNIX timestamp
416 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
418 } elseif ( $this->getLastError() ||
$timeout <= 0 ) {
419 $locked = false; // network partition or non-blocking
421 // Estimate the RTT (us); use 1ms minimum for sanity
422 $uRTT = max( 1e3
, ceil( 1e6
* ( microtime( true ) - $timestamp ) ) );
423 $sleep = 2 * $uRTT; // rough time to do get()+set()
425 $attempts = 0; // failed attempts
427 if ( ++
$attempts >= 3 && $sleep <= 5e5
) {
428 // Exponentially back off after failed attempts to avoid network spam.
429 // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
432 usleep( $sleep ); // back off
433 $this->clearLastError();
434 $locked = $this->add( "{$key}:lock", 1, $expiry );
435 if ( $this->getLastError() ) {
436 $locked = false; // network partition
439 } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
443 $this->locks
[$key] = [ 'class' => $rclass, 'depth' => 1 ];
450 * Release an advisory lock on a key string
453 * @return bool Success
455 public function unlock( $key ) {
456 if ( isset( $this->locks
[$key] ) && --$this->locks
[$key]['depth'] <= 0 ) {
457 unset( $this->locks
[$key] );
459 return $this->delete( "{$key}:lock" );
466 * Get a lightweight exclusive self-unlocking lock
468 * Note that the same lock cannot be acquired twice.
470 * This is useful for task de-duplication or to avoid obtrusive
471 * (though non-corrupting) DB errors like INSERT key conflicts
472 * or deadlocks when using LOCK IN SHARE MODE.
475 * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
476 * @param int $expiry Lock expiry [optional]; 1 day maximum
477 * @param string $rclass Allow reentry if set and the current lock used this value
478 * @return ScopedCallback|null Returns null on failure
481 final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
482 $expiry = min( $expiry ?
: INF
, self
::TTL_DAY
);
484 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
488 $lSince = microtime( true ); // lock timestamp
490 return new ScopedCallback( function() use ( $key, $lSince, $expiry ) {
491 $latency = .050; // latency skew (err towards keeping lock present)
492 $age = ( microtime( true ) - $lSince +
$latency );
493 if ( ( $age +
$latency ) >= $expiry ) {
494 $this->logger
->warning( "Lock for $key held too long ($age sec)." );
495 return; // expired; it's not "safe" to delete the key
497 $this->unlock( $key );
502 * Delete all objects expiring before a certain date.
503 * @param string $date The reference date in MW format
504 * @param callable|bool $progressCallback Optional, a function which will be called
505 * regularly during long-running operations with the percentage progress
506 * as the first parameter.
508 * @return bool Success, false if unimplemented
510 public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
516 * Get an associative array containing the item for each of the keys that have items.
517 * @param array $keys List of strings
518 * @param integer $flags Bitfield; supports READ_LATEST [optional]
521 public function getMulti( array $keys, $flags = 0 ) {
523 foreach ( $keys as $key ) {
524 $val = $this->get( $key );
525 if ( $val !== false ) {
534 * @param array $data $key => $value assoc array
535 * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
536 * @return bool Success
539 public function setMulti( array $data, $exptime = 0 ) {
541 foreach ( $data as $key => $value ) {
542 if ( !$this->set( $key, $value, $exptime ) ) {
551 * @param mixed $value
552 * @param int $exptime
553 * @return bool Success
555 public function add( $key, $value, $exptime = 0 ) {
556 if ( $this->get( $key ) === false ) {
557 return $this->set( $key, $value, $exptime );
559 return false; // key already set
563 * Increase stored value of $key by $value while preserving its TTL
564 * @param string $key Key to increase
565 * @param int $value Value to add to $key (Default 1)
566 * @return int|bool New value or false on failure
568 public function incr( $key, $value = 1 ) {
569 if ( !$this->lock( $key ) ) {
572 $n = $this->get( $key );
573 if ( $this->isInteger( $n ) ) { // key exists?
574 $n +
= intval( $value );
575 $this->set( $key, max( 0, $n ) ); // exptime?
579 $this->unlock( $key );
585 * Decrease stored value of $key by $value while preserving its TTL
588 * @return int|bool New value or false on failure
590 public function decr( $key, $value = 1 ) {
591 return $this->incr( $key, - $value );
595 * Increase stored value of $key by $value while preserving its TTL
597 * This will create the key with value $init and TTL $ttl instead if not present
603 * @return int|bool New value or false on failure
606 public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
607 $newValue = $this->incr( $key, $value );
608 if ( $newValue === false ) {
609 // No key set; initialize
610 $newValue = $this->add( $key, (int)$init, $ttl ) ?
$init : false;
612 if ( $newValue === false ) {
613 // Raced out initializing; increment
614 $newValue = $this->incr( $key, $value );
621 * Get the "last error" registered; clearLastError() should be called manually
622 * @return int ERR_* constant for the "last error" registry
625 public function getLastError() {
626 return $this->lastError
;
630 * Clear the "last error" registry
633 public function clearLastError() {
634 $this->lastError
= self
::ERR_NONE
;
638 * Set the "last error" registry
639 * @param int $err ERR_* constant
642 protected function setLastError( $err ) {
643 $this->lastError
= $err;
647 * Let a callback be run to avoid wasting time on special blocking calls
649 * The callbacks may or may not be called ever, in any particular order.
650 * They are likely to be invoked when something WRITE_SYNC is used used.
651 * They should follow a caching pattern as shown below, so that any code
652 * using the word will get it's result no matter what happens.
655 * $workCallback = function () use ( &$result ) {
663 * @param callable $workCallback
666 public function addBusyCallback( callable
$workCallback ) {
667 $this->busyCallbacks
[] = $workCallback;
671 * Modify a cache update operation array for EventRelayer::notify()
673 * This is used for relayed writes, e.g. for broadcasting a change
674 * to multiple data-centers. If the array contains a 'val' field
675 * then the command involves setting a key to that value. Note that
676 * for simplicity, 'val' is always a simple scalar value. This method
677 * is used to possibly serialize the value and add any cache-specific
678 * key/values needed for the relayer daemon (e.g. memcached flags).
680 * @param array $event
684 public function modifySimpleRelayEvent( array $event ) {
689 * @param string $text
691 protected function debug( $text ) {
692 if ( $this->debugMode
) {
693 $this->logger
->debug( "{class} debug: $text", [
694 'class' => get_class( $this ),
700 * Convert an optionally relative time to an absolute time
701 * @param int $exptime
704 protected function convertExpiry( $exptime ) {
705 if ( $exptime != 0 && $exptime < ( 10 * self
::TTL_YEAR
) ) {
706 return time() +
$exptime;
713 * Convert an optionally absolute expiry time to a relative time. If an
714 * absolute time is specified which is in the past, use a short expiry time.
716 * @param int $exptime
719 protected function convertToRelative( $exptime ) {
720 if ( $exptime >= ( 10 * self
::TTL_YEAR
) ) {
722 if ( $exptime <= 0 ) {
732 * Check if a value is an integer
734 * @param mixed $value
737 protected function isInteger( $value ) {
738 return ( is_int( $value ) ||
ctype_digit( $value ) );
742 * Construct a cache key.
745 * @param string $keyspace
749 public function makeKeyInternal( $keyspace, $args ) {
751 foreach ( $args as $arg ) {
752 $arg = str_replace( ':', '%3A', $arg );
753 $key = $key . ':' . $arg;
755 return strtr( $key, ' ', '_' );
759 * Make a global cache key.
762 * @param string ... Key component (variadic)
765 public function makeGlobalKey() {
766 return $this->makeKeyInternal( 'global', func_get_args() );
770 * Make a cache key, scoped to this instance's keyspace.
773 * @param string ... Key component (variadic)
776 public function makeKey() {
777 return $this->makeKeyInternal( $this->keyspace
, func_get_args() );
781 * @param integer $flag ATTR_* class constant
782 * @return integer QOS_* class constant
785 public function getQoS( $flag ) {
786 return isset( $this->attrMap
[$flag] ) ?
$this->attrMap
[$flag] : self
::QOS_UNKNOWN
;
790 * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
792 * @param BagOStuff[] $bags
793 * @return integer[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
795 protected function mergeFlagMaps( array $bags ) {
797 foreach ( $bags as $bag ) {
798 foreach ( $bag->attrMap
as $attr => $rank ) {
799 if ( isset( $map[$attr] ) ) {
800 $map[$attr] = min( $map[$attr], $rank );