聊聊maxwell的PositionStoreThread

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序

本文主要研究一下maxwell的PositionStoreThread

PositionStoreThread

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/schema/PositionStoreThread.java

public class PositionStoreThread extends RunLoopProcess implements Runnable {
    static final Logger LOGGER = LoggerFactory.getLogger(PositionStoreThread.class);
    private Position position; // in memory position
    private Position storedPosition; // position as flushed to storage
    private final MysqlPositionStore store;
    private MaxwellContext context;
    private Exception exception;
    private Thread thread;
    private BinlogPosition lastHeartbeatSentFrom; // last position we sent a heartbeat from
    private long lastHeartbeatSent;

    public PositionStoreThread(MysqlPositionStore store, MaxwellContext context) {
        this.store = store;
        this.context = context;
        lastHeartbeatSentFrom = null;
        lastHeartbeatSent = 0L;
    }

    public void start() {
        this.thread = new Thread(this, "Position Flush Thread");
        this.thread.setDaemon(true);
        thread.start();
    }

    @Override
    public void run() {
        try {
            runLoop();
        } catch ( Exception e ) {
            this.exception = e;
            context.terminate(e);
        } finally {
            this.taskState.stopped();
        }
    }

    @Override
    protected void beforeStop() {
        if ( exception == null ) {
            try {
                storeFinalPosition();
            } catch ( Exception e ) {
                LOGGER.error("error storing final position: " + e);
            }
        }
    }

    void storeFinalPosition() throws SQLException, DuplicateProcessException {
        if ( position != null && !position.equals(storedPosition) ) {
            LOGGER.info("Storing final position: " + position);
            store.set(position);
        }
    }

    public void heartbeat() throws Exception {
        store.heartbeat();
    }

    boolean shouldHeartbeat(Position currentPosition) {
        if ( currentPosition == null )
            return true;
        if ( lastHeartbeatSentFrom == null )
            return true;

        BinlogPosition currentBinlog = currentPosition.getBinlogPosition();
        if ( !lastHeartbeatSentFrom.getFile().equals(currentBinlog.getFile()) )
            return true;
        if ( currentBinlog.getOffset() - lastHeartbeatSentFrom.getOffset() > 1000 ) {
            return true;
        }

        long secondsSinceHeartbeat = (System.currentTimeMillis() - lastHeartbeatSent) / 1000;
        if ( secondsSinceHeartbeat >= 10 ) {
            // during quiet times, heartbeat at least every 10s
            return true;
        }

        return false;
    }

    public void work() throws Exception {
        Position newPosition = position;

        if ( newPosition != null && newPosition.newerThan(storedPosition) ) {
            store.set(newPosition);
            storedPosition = newPosition;
        }

        try { Thread.sleep(1000); } catch (InterruptedException e) { }

        if ( shouldHeartbeat(newPosition) )  {
            lastHeartbeatSent = store.heartbeat();
            if (newPosition != null) {
                lastHeartbeatSentFrom = newPosition.getBinlogPosition();
            }
        }
    }

    public synchronized void setPosition(Position p) {
        if ( position == null || p.newerThan(position) ) {
            position = p;
            if (storedPosition == null) {
                storedPosition = p;
            }
        }
    }

    public synchronized Position getPosition() throws SQLException {
        if ( position != null )
            return position;

        position = store.get();

        return position;
    }
}

• PositionStoreThread继承了RunLoopProcess，实现了Runnable，其run方法执行runLoop；其beforeStop方法执行storeFinalPosition方法；该方法在判断position与storedPosition不等时更新position到store；其work方法会更新newPosition到store，然后判断是否需要hearbeat，需要的话执行store.heartbeat()；shouldHeartbeat方法在currentBinlog.getOffset()与lastHeartbeatSentFrom.getOffset()差值大于1000时返回true，在secondsSinceHeartbeat大于等于10的时候返回true

MaxwellContext

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/MaxwellContext.java

public class MaxwellContext {

    //......

    public PositionStoreThread getPositionStoreThread() {
        if ( this.positionStoreThread == null ) {
            this.positionStoreThread = new PositionStoreThread(this.positionStore, this);
            this.positionStoreThread.start();
            addTask(positionStoreThread);
        }
        return this.positionStoreThread;
    }

    public void addTask(StoppableTask task) {
        this.taskManager.add(task);
    }

    private void shutdown(AtomicBoolean complete) {
        try {
            taskManager.stop(this.error);
            this.replicationConnectionPool.release();
            this.maxwellConnectionPool.release();
            this.rawMaxwellConnectionPool.release();
            complete.set(true);
        } catch (Exception e) {
            LOGGER.error("Exception occurred during shutdown:", e);
        }
    }

    //......

}

• MaxwellContext提供了getPositionStoreThread方法，在positionStoreThread为null的时候会创建一个positionStoreThread并执行其start方法，同时执行addTask方法；addTask将StoppableTask添加到taskManager中；其shutdown方法会执行taskManager.stop

TaskManager

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/util/TaskManager.java

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

    private final ArrayList<stoppabletask> tasks;
    private volatile RunState state;

    public TaskManager() {
        this.tasks = new ArrayList();
        this.state = RunState.RUNNING;
    }

    // Can be invoked multiple times, will only return `true`
    // for the first invocation.
    public synchronized boolean requestStop() {
        if (state == RunState.RUNNING) {
            state = RunState.REQUEST_STOP;
            return true;
        } else {
            return false;
        }
    }

    public synchronized void stop(Exception error) throws Exception {
        if (this.state == RunState.STOPPED) {
            LOGGER.debug("Stop() called multiple times");
            return;
        }
        this.state = RunState.REQUEST_STOP;

        LOGGER.info("Stopping " + tasks.size() + " tasks");

        if (error != null) {
            LOGGER.error("cause: ", error);
        }

        // tell everything to stop
        for (StoppableTask task: this.tasks) {
            LOGGER.info("Stopping: " + task);
            task.requestStop();
        }

        // then wait for everything to stop
        Long timeout = 1000L;
        for (StoppableTask task: this.tasks) {
            LOGGER.debug("Awaiting stop of: " + task);
            task.awaitStop(timeout);
        }

        this.state = RunState.STOPPED;
        LOGGER.info("Stopped all tasks");
    }

    public synchronized void add(StoppableTask task) {
        synchronized (tasks) {
            tasks.add(task);
        }
    }
}</stoppabletask>

• TaskManager的add方法会将task添加到tasks中；其requestStop方法会设置state为RunState.REQUEST_STOP；其stop方法先设置state为RunState.REQUEST_STOP，然后遍历tasks挨个执行task.requestStop()，之后在执行task.awaitStop(timeout)，最后更新state为RunState.STOPPED

小结

PositionStoreThread继承了RunLoopProcess，实现了Runnable，其run方法执行runLoop；其beforeStop方法执行storeFinalPosition方法；该方法在判断position与storedPosition不等时更新position到store；其work方法会更新newPosition到store，然后判断是否需要hearbeat，需要的话执行store.heartbeat()；shouldHeartbeat方法在currentBinlog.getOffset()与lastHeartbeatSentFrom.getOffset()差值大于1000时返回true，在secondsSinceHeartbeat大于等于10的时候返回true

doc

• PositionStoreThread

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