MySqlLockManager.php

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<?php
 
use Wikimedia\Rdbms\IDatabase;
use Wikimedia\Rdbms\DBError;
 
class MySqlLockManager extends DBLockManager {
    protected $lockTypeMap = [
        self::LOCK_SH => self::LOCK_SH,
        self::LOCK_UW => self::LOCK_SH,
        self::LOCK_EX => self::LOCK_EX
    ];
 
    public function __construct( array $config ) {
        parent::__construct( $config );
 
        $this->session = substr( $this->session, 0, 31 ); // fit to field
    }
 
    protected function initConnection( $lockDb, IDatabase $db ) {
        # Let this transaction see lock rows from other transactions
        $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
        # Do everything in a transaction as it all gets rolled back eventually
        $db->startAtomic( __CLASS__ );
    }
 
    protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
        $status = StatusValue::newGood();
 
        $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
 
        $keys = []; // list of hash keys for the paths
        $data = []; // list of rows to insert
        $checkEXKeys = []; // list of hash keys that this has no EX lock on
        # Build up values for INSERT clause
        foreach ( $paths as $path ) {
            $key = $this->sha1Base36Absolute( $path );
            $keys[] = $key;
            $data[] = [ 'fls_key' => $key, 'fls_session' => $this->session ];
            if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
                $checkEXKeys[] = $key; // this has no EX lock on $key itself
            }
        }
 
        # Block new writers (both EX and SH locks leave entries here)...
        $db->insert( 'filelocks_shared', $data, __METHOD__, [ 'IGNORE' ] );
        # Actually do the locking queries...
        if ( $type == self::LOCK_SH ) { // reader locks
            # Bail if there are any existing writers...
            if ( count( $checkEXKeys ) ) {
                $blocked = $db->selectField(
                    'filelocks_exclusive',
                    '1',
                    [ 'fle_key' => $checkEXKeys ],
                    __METHOD__
                );
            } else {
                $blocked = false;
            }
            # Other prospective writers that haven't yet updated filelocks_exclusive
            # will recheck filelocks_shared after doing so and bail due to this entry.
        } else { // writer locks
            $encSession = $db->addQuotes( $this->session );
            # Bail if there are any existing writers...
            # This may detect readers, but the safe check for them is below.
            # Note: if two writers come at the same time, both bail :)
            $blocked = $db->selectField(
                'filelocks_shared',
                '1',
                [ 'fls_key' => $keys, "fls_session != $encSession" ],
                __METHOD__
            );
            if ( !$blocked ) {
                # Build up values for INSERT clause
                $data = [];
                foreach ( $keys as $key ) {
                    $data[] = [ 'fle_key' => $key ];
                }
                # Block new readers/writers...
                $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
                # Bail if there are any existing readers...
                $blocked = $db->selectField(
                    'filelocks_shared',
                    '1',
                    [ 'fls_key' => $keys, "fls_session != $encSession" ],
                    __METHOD__
                );
            }
        }
 
        if ( $blocked ) {
            foreach ( $paths as $path ) {
                $status->fatal( 'lockmanager-fail-acquirelock', $path );
            }
        }
 
        return $status;
    }
 
    protected function releaseAllLocks() {
        $status = StatusValue::newGood();
 
        foreach ( $this->conns as $lockDb => $db ) {
            if ( $db->trxLevel() ) { // in transaction
                try {
                    $db->rollback( __METHOD__ ); // finish transaction and kill any rows
                } catch ( DBError $e ) {
                    $status->fatal( 'lockmanager-fail-db-release', $lockDb );
                }
            }
        }
 
        return $status;
    }
}