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| 1 | <?php |
| 2 | /** |
| 3 | * This program is free software; you can redistribute it and/or modify |
| 4 | * it under the terms of the GNU General Public License as published by |
| 5 | * the Free Software Foundation; either version 2 of the License, or |
| 6 | * (at your option) any later version. |
| 7 | * |
| 8 | * This program is distributed in the hope that it will be useful, |
| 9 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 10 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 11 | * GNU General Public License for more details. |
| 12 | * |
| 13 | * You should have received a copy of the GNU General Public License along |
| 14 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 15 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
| 16 | * http://www.gnu.org/copyleft/gpl.html |
| 17 | * |
| 18 | * @file |
| 19 | */ |
| 20 | |
| 21 | namespace MediaWiki\PoolCounter; |
| 22 | |
| 23 | use MediaWiki\MediaWikiServices; |
| 24 | use MediaWiki\Status\Status; |
| 25 | |
| 26 | /** |
| 27 | * Class for dealing with PoolCounters using class members |
| 28 | */ |
| 29 | abstract class PoolCounterWork { |
| 30 | /** @var string */ |
| 31 | protected $type = 'generic'; |
| 32 | /** @var bool */ |
| 33 | protected $cacheable = false; // does this override getCachedWork() ? |
| 34 | /** @var PoolCounter */ |
| 35 | private $poolCounter; |
| 36 | |
| 37 | /** |
| 38 | * @param string $type The class of actions to limit concurrency for (task type) |
| 39 | * @param string $key Key that identifies the queue this work is placed on |
| 40 | * @param PoolCounter|null $poolCounter |
| 41 | */ |
| 42 | public function __construct( string $type, string $key, PoolCounter $poolCounter = null ) { |
| 43 | $this->type = $type; |
| 44 | // MW >= 1.35 |
| 45 | $this->poolCounter = $poolCounter ?? |
| 46 | MediaWikiServices::getInstance()->getPoolCounterFactory()->create( $type, $key ); |
| 47 | } |
| 48 | |
| 49 | /** |
| 50 | * Actually perform the work, caching it if needed |
| 51 | * |
| 52 | * @return mixed|false Work result or false |
| 53 | */ |
| 54 | abstract public function doWork(); |
| 55 | |
| 56 | /** |
| 57 | * Retrieve the work from cache |
| 58 | * |
| 59 | * @return mixed|false Work result or false |
| 60 | */ |
| 61 | public function getCachedWork() { |
| 62 | return false; |
| 63 | } |
| 64 | |
| 65 | /** |
| 66 | * A work not so good (eg. expired one) but better than an error |
| 67 | * message. |
| 68 | * |
| 69 | * @param bool $fast True if PoolCounter is requesting a fast stale response (pre-wait) |
| 70 | * @return mixed|false Work result or false |
| 71 | */ |
| 72 | public function fallback( $fast ) { |
| 73 | return false; |
| 74 | } |
| 75 | |
| 76 | /** |
| 77 | * Do something with the error, like showing it to the user. |
| 78 | * |
| 79 | * @param Status $status |
| 80 | * @return mixed|false |
| 81 | */ |
| 82 | public function error( $status ) { |
| 83 | return false; |
| 84 | } |
| 85 | |
| 86 | /** |
| 87 | * Should fast stale mode be used? |
| 88 | * |
| 89 | * @return bool |
| 90 | */ |
| 91 | protected function isFastStaleEnabled() { |
| 92 | return $this->poolCounter->isFastStaleEnabled(); |
| 93 | } |
| 94 | |
| 95 | /** |
| 96 | * Log an error |
| 97 | * |
| 98 | * @param Status $status |
| 99 | * @return void |
| 100 | */ |
| 101 | public function logError( $status ) { |
| 102 | $key = $this->poolCounter->getKey(); |
| 103 | |
| 104 | $this->poolCounter->getLogger()->info( |
| 105 | "Pool key '$key' ({$this->type}): " . |
| 106 | $status->getMessage()->inLanguage( 'en' )->useDatabase( false )->text() |
| 107 | ); |
| 108 | } |
| 109 | |
| 110 | /** |
| 111 | * Get the result of the work (whatever it is), or the result of the error() function. |
| 112 | * |
| 113 | * This returns the result of the one of the following methods: |
| 114 | * |
| 115 | * - doWork(): Applies if the work is exclusive or no other process |
| 116 | * is doing it, and on the condition that either this process |
| 117 | * successfully entered the pool or the pool counter is down. |
| 118 | * - doCachedWork(): Applies if the work is cacheable and this blocked on another |
| 119 | * process which finished the work. |
| 120 | * - fallback(): Applies for all remaining cases. |
| 121 | * |
| 122 | * If these all return false, then the result of error() is returned. |
| 123 | * |
| 124 | * In slow-stale mode, these three methods are called in the sequence given above, and |
| 125 | * the first non-false response is used. This means in case of concurrent cache-miss requests |
| 126 | * for the same revision, later ones will load on DBs and other backend services, and wait for |
| 127 | * earlier requests to succeed and then read out their saved result. |
| 128 | * |
| 129 | * In fast-stale mode, if other requests hold doWork lock already, we call fallback() first |
| 130 | * to let it try to find an acceptable return value. If fallback() returns false, then we |
| 131 | * will wait for the doWork lock, as for slow stale mode, including potentially calling |
| 132 | * fallback() a second time. |
| 133 | * |
| 134 | * @param bool $skipcache |
| 135 | * @return mixed |
| 136 | */ |
| 137 | public function execute( $skipcache = false ) { |
| 138 | if ( !$this->cacheable || $skipcache ) { |
| 139 | $status = $this->poolCounter->acquireForMe(); |
| 140 | } else { |
| 141 | if ( $this->isFastStaleEnabled() ) { |
| 142 | // In fast stale mode, check for existing locks by acquiring lock with 0 timeout |
| 143 | $status = $this->poolCounter->acquireForAnyone( 0 ); |
| 144 | if ( $status->isOK() && $status->value === PoolCounter::TIMEOUT ) { |
| 145 | // Lock acquisition would block: try fallback |
| 146 | $staleResult = $this->fallback( true ); |
| 147 | if ( $staleResult !== false ) { |
| 148 | return $staleResult; |
| 149 | } |
| 150 | // No fallback available, so wait for the lock |
| 151 | $status = $this->poolCounter->acquireForAnyone(); |
| 152 | } // else behave as if $status were returned in slow mode |
| 153 | } else { |
| 154 | $status = $this->poolCounter->acquireForAnyone(); |
| 155 | } |
| 156 | } |
| 157 | |
| 158 | if ( !$status->isOK() ) { |
| 159 | // Respond gracefully to complete server breakage: just log it and do the work |
| 160 | $this->logError( $status ); |
| 161 | return $this->doWork(); |
| 162 | } |
| 163 | |
| 164 | switch ( $status->value ) { |
| 165 | case PoolCounter::LOCK_HELD: |
| 166 | // Better to ignore nesting pool counter limits than to fail. |
| 167 | // Assume that the outer pool limiting is reasonable enough. |
| 168 | /* no break */ |
| 169 | case PoolCounter::LOCKED: |
| 170 | try { |
| 171 | return $this->doWork(); |
| 172 | } finally { |
| 173 | $this->poolCounter->release(); |
| 174 | } |
| 175 | // no fall-through, because try returns or throws |
| 176 | case PoolCounter::DONE: |
| 177 | $result = $this->getCachedWork(); |
| 178 | if ( $result === false ) { |
| 179 | /* That someone else work didn't serve us. |
| 180 | * Acquire the lock for me |
| 181 | */ |
| 182 | return $this->execute( true ); |
| 183 | } |
| 184 | return $result; |
| 185 | |
| 186 | case PoolCounter::QUEUE_FULL: |
| 187 | case PoolCounter::TIMEOUT: |
| 188 | $result = $this->fallback( false ); |
| 189 | |
| 190 | if ( $result !== false ) { |
| 191 | return $result; |
| 192 | } |
| 193 | /* no break */ |
| 194 | |
| 195 | /* These two cases should never be hit... */ |
| 196 | case PoolCounter::ERROR: |
| 197 | default: |
| 198 | $errors = [ |
| 199 | PoolCounter::QUEUE_FULL => 'pool-queuefull', |
| 200 | PoolCounter::TIMEOUT => 'pool-timeout', |
| 201 | ]; |
| 202 | |
| 203 | $status = Status::newFatal( $errors[$status->value] ?? 'pool-errorunknown' ); |
| 204 | $this->logError( $status ); |
| 205 | return $this->error( $status ); |
| 206 | } |
| 207 | } |
| 208 | } |
| 209 | |
| 210 | /** @deprecated class alias since 1.41 */ |
| 211 | class_alias( PoolCounterWork::class, 'PoolCounterWork' ); |