order

This paper focuses on the masterelement of chronos

MasterElection

DDMQ/carrera-chronos/src/main/java/com/xiaojukeji/chronos/ha/MasterElection.java

public class MasterElection {
    private static final Logger SWITCH_LOGGER = LogUtils.SWITCH_LOGGER;

    private static volatile ServerState state = ServerState.BACKUPING;

    public static void election(final CountDownLatch cdl) {
        final CuratorFramework client = ZkUtils.getCuratorClient();
        final LeaderSelector selector = new LeaderSelector(client, Constants.MASTER_PATH, new LeaderSelectorListenerAdapter() {
            @Override
            public void takeLeadership(CuratorFramework curatorFramework) throws Exception {
                SWITCH_LOGGER.info("take master leadership");

                long seekTimestamp = MetaService.getSeekTimestamp();
                long zkSeekTimestamp = MetaService.getZkSeekTimestamp();
                final long sleepMs = 200;
                long sleepCount = 0;
                // If the data on the zk is lost, the zkSeekTimestamp is 0, and the chronos is block ed
                while (seekTimestamp < zkSeekTimestamp && zkSeekTimestamp > 0) {
                    SWITCH_LOGGER.info("sleep {}ms to wait seekTimestamp:{} to catch up with zkSeekTimestamp:{}",
                            sleepMs, seekTimestamp, zkSeekTimestamp);
                    TimeUnit.MILLISECONDS.sleep(sleepMs);
                    seekTimestamp = MetaService.getSeekTimestamp();
                    zkSeekTimestamp = MetaService.getZkSeekTimestamp();
                    sleepCount++;
                }

                state = ServerState.MASTERING;
                SWITCH_LOGGER.info("change server state to {}, totalSleepMs:{}ms", state, sleepCount * sleepMs);
                cdl.await();
                state = ServerState.BACKUPING;
                SWITCH_LOGGER.info("release master leadership");
            }
        });
        selector.autoRequeue();
        selector.start();
    }

    public static boolean isMaster() {
        return state == ServerState.MASTERING;
    }

    public static boolean isBackup() {
        return state == ServerState.BACKUPING;
    }

    public static void standAlone() {
        state = ServerState.MASTERING;
    }

    public static ServerState getState() {
        return state;
    }
}

• MasterElection provides the methods of election, isMaster, isBackup, standAlone and getState. The method of election uses the leader selector of cursor recipes, whose leader selectorlisteneradapter's takeLeadership method will first obtain seekTimestamp and zkSeekTimestamp, and use while loop until seekTimestamp is greater than or equal to zkSeekTimestamp, and then update the state to serversta Te.MASTERING, then call CountDownLatch's await method, then update state to ServerState.BACKUPING, release leadership; after creating LeaderSelector, call autoRequeue and start methods.

ChronosStartup

DDMQ/carrera-chronos/src/main/java/com/xiaojukeji/chronos/ChronosStartup.java

public class ChronosStartup {
    private static final Logger LOGGER = LoggerFactory.getLogger(ChronosStartup.class);

    private CountDownLatch waitForShutdown;
    private String configFilePath = "chronos.yaml";
    private PullWorker pullWorker;
    private PushWorker pushWorker;
    private DeleteBgWorker deleteBgWorker;
    private NettyHttpServer nettyHttpServer;

    ChronosStartup(final String configFilePath) {
        if (StringUtils.isNotBlank(configFilePath)) {
            this.configFilePath = configFilePath;
        }
    }

    public void start() throws Exception {
        LOGGER.info("start to launch chronos...");
        final long start = System.currentTimeMillis();

        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                try {
                    LOGGER.info("start to stop chronos...");
                    final long start = System.currentTimeMillis();
                    ChronosStartup.this.stop();
                    final long cost = System.currentTimeMillis() - start;
                    LOGGER.info("succ stop chronos, cost:{}ms", cost);
                } catch (Exception e) {
                    LOGGER.error("error while shutdown chronos, err:{}", e.getMessage(), e);
                } finally {
                    /* shutdown log4j2 */
                    LogManager.shutdown();
                }
            }
        });

        /* Note: the following initialization sequence is in order */

        /* init config */
        ConfigManager.initConfig(configFilePath);

        /* init metrics */
        if (!MetricService.init()) {
            System.exit(-1);
        }

        /* init rocksdb */
        RDB.init(ConfigManager.getConfig().getDbConfig().getDbPath());

        /* init zk */
        ZkUtils.init();

        /* init seektimestamp */
        MetaService.load();

        waitForShutdown = new CountDownLatch(1);

        if (ConfigManager.getConfig().isStandAlone()) {
            /* standalone */
            MasterElection.standAlone();
        } else {
            /* Cluster mode master election */
            MasterElection.election(waitForShutdown);
        }

        /* init pull worker */
        if (ConfigManager.getConfig().isPullOn()) {
            pullWorker = PullWorker.getInstance();
            pullWorker.start();
        }

        /* init push worker */
        if (ConfigManager.getConfig().isPushOn()) {
            pushWorker = PushWorker.getInstance();
            pushWorker.start();
        }

        /* init delete worker */
        if (ConfigManager.getConfig().isDeleteOn()) {
            deleteBgWorker = DeleteBgWorker.getInstance();
            deleteBgWorker.start();
        }

        final long cost = System.currentTimeMillis() - start;
        LOGGER.info("succ start chronos, cost:{}ms", cost);

        /* init http server */
        nettyHttpServer = NettyHttpServer.getInstance();
        nettyHttpServer.start();

        waitForShutdown.await();
    }

    void stop() {
        /* shutdown netty http server */
        if (nettyHttpServer != null) {
            nettyHttpServer.shutdown();
        }

        /* stop pull from MQ */
        if (pullWorker != null) {
            pullWorker.stop();
        }

        /* stop push to MQ */
        if (pushWorker != null) {
            pushWorker.stop();
        }

        /* stop delete */
        if (deleteBgWorker != null) {
            deleteBgWorker.stop();
        }

        MqConsumeStatService.getInstance().stop();

        /* close zk client */
        ZkUtils.close();

        /* close rocksdb */
        RDB.close();

        if (waitForShutdown != null) {
            waitForShutdown.countDown();
            waitForShutdown = null;
        }
    }
}

• ChronosStartup's start method will create waitForShutdown, and execute MasterElection.election(waitForShutdown) for non standlone mode

Summary

MasterElection provides the methods of election, isMaster, isBackup, standAlone and getState. The method of election uses the leader selector of cursor recipes, whose leader selectorlisteneradapter's takeLeadership method will first obtain seekTimestamp and zkSeekTimestamp, and use while loop until seekTimestamp is greater than or equal to zkSeekTimestamp, and then update the state to serversta Te.MASTERING, then call CountDownLatch's await method, then update state to ServerState.BACKUPING, release leadership; after creating LeaderSelector, call autoRequeue and start methods.

doc

• carrera-chronos
• Talk about the leader latch of Creator recipes