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<?php |
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declare( strict_types = 1 ); |
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namespace IdGenerator\PackagePrivate; |
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use IdGenerator\IdGenerator; |
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use RuntimeException; |
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use Wikimedia\Rdbms\IDatabase; |
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use Wikimedia\Rdbms\ILoadBalancer; |
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class PagePropsIdGenerator implements IdGenerator { |
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private const FAKE_PAGE_ID = -42; |
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private $loadBalancer; |
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public function __construct( ILoadBalancer $loadBalancer ) { |
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$this->loadBalancer = $loadBalancer; |
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} |
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public function getNewId( string $type = '' ): int { |
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$database = $this->loadBalancer->getConnection( DB_MASTER ); |
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$id = $this->generateNewId( $database, $type ); |
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$this->loadBalancer->reuseConnection( $database ); |
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return $id; |
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} |
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/** |
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* Generates and returns a new ID. |
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* |
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* @param IDatabase $database |
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* @param string $type |
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* @param bool $retry Retry once in case of e.g. race conditions. Defaults to true. |
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* |
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* @throws RuntimeException |
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* @return int |
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*/ |
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private function generateNewId( IDatabase $database, string $type, $retry = true ): int { |
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$database->startAtomic( __METHOD__ ); |
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$currentId = $database->selectRow( |
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'page_props', |
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'pp_value', |
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$this->getWhere( $type ), |
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__METHOD__, |
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[ 'FOR UPDATE' ] |
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); |
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if ( is_object( $currentId ) ) { |
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$id = $currentId->id_value + 1; |
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$success = $database->update( |
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'page_props', |
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[ 'pp_value' => $id ], |
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$this->getWhere( $type ) |
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); |
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} else { |
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$id = 1; |
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$success = $database->insert( |
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'page_props', |
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$this->getInsertValues( $type, $id ) |
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); |
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// Retry once, since a race condition on initial insert can cause one to fail. |
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// Race condition is possible due to occurrence of phantom reads is possible |
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// at non serializable transaction isolation level. |
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if ( !$success && $retry ) { |
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$id = $this->generateNewId( $database, $type, false ); |
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$success = true; |
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} |
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} |
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$database->endAtomic( __METHOD__ ); |
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if ( !$success ) { |
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throw new RuntimeException( 'Could not generate a reliably unique ID.' ); |
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} |
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return $id; |
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} |
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private function getInsertValues( string $idType, int $id ): array { |
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$values = $this->getWhere( $idType ); |
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$values['pp_value'] = $id; |
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return $values; |
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} |
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private function getWhere( string $idType ): array { |
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return [ |
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'pp_page' => self::FAKE_PAGE_ID, |
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'pp_propname' => $this->makePropertyName( $idType ) |
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]; |
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} |
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private function makePropertyName( string $idType ): string { |
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return 'id_' . $idType; |
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} |
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} |
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ProfessionalWiki /
IdGenerator
