ChronologyProtector.php

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<?php
class ChronologyProtector {
    protected $startupPositions = array();
    protected $shutdownPositions = array();

    protected $initialized = false; // bool; whether the session data was loaded

    public function initLB( LoadBalancer $lb ) {
        if ( $lb->getServerCount() <= 1 ) {
            return; // non-replicated setup
        }
        if ( !$this->initialized ) {
            $this->initialized = true;
            if ( isset( $_SESSION[__CLASS__] ) && is_array( $_SESSION[__CLASS__] ) ) {
                $this->startupPositions = $_SESSION[__CLASS__];
            }
        }
        $masterName = $lb->getServerName( 0 );
        if ( !empty( $this->startupPositions[$masterName] ) ) {
            $info = $lb->parentInfo();
            $pos = $this->startupPositions[$masterName];
            wfDebug( __METHOD__ . ": LB " . $info['id'] . " waiting for master pos $pos\n" );
            $lb->waitFor( $pos );
        }
    }

    public function shutdownLB( LoadBalancer $lb ) {
        if ( session_id() == '' || $lb->getServerCount() <= 1 ) {
            return; // don't start a session; don't bother with non-replicated setups
        }
        $masterName = $lb->getServerName( 0 );
        if ( isset( $this->shutdownPositions[$masterName] ) ) {
            return; // already done
        }
        // Only save the position if writes have been done on the connection
        $db = $lb->getAnyOpenConnection( 0 );
        $info = $lb->parentInfo();
        if ( !$db || !$db->doneWrites() ) {
            wfDebug( __METHOD__ . ": LB {$info['id']}, no writes done\n" );
            return;
        }
        $pos = $db->getMasterPos();
        wfDebug( __METHOD__ . ": LB {$info['id']} has master pos $pos\n" );
        $this->shutdownPositions[$masterName] = $pos;
    }

    public function shutdown() {
        if ( session_id() != '' && count( $this->shutdownPositions ) ) {
            wfDebug( __METHOD__ . ": saving master pos for " .
                count( $this->shutdownPositions ) . " master(s)\n" );
            $_SESSION[__CLASS__] = $this->shutdownPositions;
        }
    }
}