ChronologyProtector.php

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<?php
class ChronologyProtector {
    protected $store;

    protected $key;
    protected $client;
    protected $enabled = true;
    protected $wait = true;

    protected $initialized = false;
    protected $startupPositions = [];
    protected $shutdownPositions = [];

    public function __construct( BagOStuff $store, array $client ) {
        $this->store = $store;
        $this->client = $client;
        $this->key = $store->makeGlobalKey(
            'ChronologyProtector',
            md5( $client['ip'] . "\n" . $client['agent'] )
        );
    }

    public function setEnabled( $enabled ) {
        $this->enabled = $enabled;
    }

    public function setWaitEnabled( $enabled ) {
        $this->wait = $enabled;
    }

    public function initLB( LoadBalancer $lb ) {
        if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
            return; // non-replicated setup or disabled
        }

        $this->initPositions();

        $masterName = $lb->getServerName( $lb->getWriterIndex() );
        if ( !empty( $this->startupPositions[$masterName] ) ) {
            $info = $lb->parentInfo();
            $pos = $this->startupPositions[$masterName];
            wfDebugLog( 'replication', __METHOD__ .
                ": LB '" . $info['id'] . "' waiting for master pos $pos\n" );
            $lb->waitFor( $pos );
        }
    }

    public function shutdownLB( LoadBalancer $lb ) {
        if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
            return; // non-replicated setup or disabled
        }

        $info = $lb->parentInfo();
        $masterName = $lb->getServerName( $lb->getWriterIndex() );

        // Only save the position if writes have been done on the connection
        $db = $lb->getAnyOpenConnection( $lb->getWriterIndex() );
        if ( !$db || !$db->doneWrites() ) {
            wfDebugLog( 'replication', __METHOD__ . ": LB {$info['id']}, no writes done\n" );

            return; // nothing to do
        }

        $pos = $db->getMasterPos();
        wfDebugLog( 'replication', __METHOD__ . ": LB {$info['id']} has master pos $pos\n" );
        $this->shutdownPositions[$masterName] = $pos;
    }

    public function shutdown() {
        if ( !$this->enabled || !count( $this->shutdownPositions ) ) {
            return true; // nothing to save
        }

        wfDebugLog( 'replication',
            __METHOD__ . ": saving master pos for " .
            implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
        );

        $shutdownPositions = $this->shutdownPositions;
        $ok = $this->store->merge(
            $this->key,
            function ( $store, $key, $curValue ) use ( $shutdownPositions ) {
                if ( $curValue === false ) {
                    $curPositions = $shutdownPositions;
                } else {
                    $curPositions = $curValue['positions'];
                    // Use the newest positions for each DB master
                    foreach ( $shutdownPositions as $db => $pos ) {
                        if ( !isset( $curPositions[$db] )
                            || $pos->asOfTime() > $curPositions[$db]->asOfTime()
                        ) {
                            $curPositions[$db] = $pos;
                        }
                    }
                }

                return [ 'positions' => $curPositions ];
            },
            BagOStuff::TTL_MINUTE,
            10,
            BagOStuff::WRITE_SYNC // visible in all datacenters
        );

        if ( !$ok ) {
            // Raced out too many times or stash is down
            wfDebugLog( 'replication',
                __METHOD__ . ": failed to save master pos for " .
                implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
            );

            return $this->shutdownPositions;
        }

        return [];
    }

    protected function initPositions() {
        if ( $this->initialized ) {
            return;
        }

        $this->initialized = true;
        if ( $this->wait ) {
            $data = $this->store->get( $this->key );
            $this->startupPositions = $data ? $data['positions'] : [];

            wfDebugLog( 'replication', __METHOD__ . ": key is {$this->key} (read)\n" );
        } else {
            $this->startupPositions = [];

            wfDebugLog( 'replication', __METHOD__ . ": key is {$this->key} (unread)\n" );
        }
    }
}