dubbo使用的zk客户端
在使用dubbo的过程中,当注册中心的数据修改后,新的配置是怎样刷到consumer和provider的?本文以consumer为例,进行分析。
dubbo使用的是zkclient的jar,而zkclient依赖zookeeper的jar。
示例代码:
- public class MyI0zk {
- public static void main(String[] args) {
- ZkClient zkclient = new ZkClient("127.0.0.1:2181");
- int countChildren = zkclient.countChildren("/");
- System.out.println(countChildren);
- }
- }
调用栈如下图:
在connect方法中创建了ZooKeeper对象:
- // void org.I0Itec.zkclient.ZkConnection.connect(Watcher watcher)
- public void connect(Watcher watcher) {
- _zookeeperLock.lock();
- try {
- if (_zk != null) {
- throw new IllegalStateException("zk client has already been started");
- }
- try {
- LOG.debug("Creating new ZookKeeper instance to connect to " + _servers + ".");
- _zk = new ZooKeeper(_servers, _sessionTimeOut, watcher);
- } catch (IOException e) {
- throw new ZkException("Unable to connect to " + _servers, e);
- }
- } finally {
- _zookeeperLock.unlock();
- }
- }
ZkClient自身就是一个Watcher:
- //省略其他代码
- public class ZkClient implements Watcher {
- public void process(WatchedEvent event) {
- LOG.debug("Received event: " + event);
- _zookeeperEventThread = Thread.currentThread();
- boolean stateChanged = event.getPath() == null;
- boolean znodeChanged = event.getPath() != null;
- boolean dataChanged = event.getType() == EventType.NodeDataChanged || event.getType() == EventType.NodeDeleted || event.getType() == EventType.NodeCreated
- || event.getType() == EventType.NodeChildrenChanged;
- getEventLock().lock();
- try {
- // We might have to install child change event listener if a new node was created
- if (getShutdownTrigger()) {
- LOG.debug("ignoring event '{" + event.getType() + " | " + event.getPath() + "}' since shutdown triggered");
- return;
- }
- if (stateChanged) {
- processStateChanged(event);
- }
- if (dataChanged) {
- processDataOrChildChange(event);
- }
- } finally {
- if (stateChanged) {
- getEventLock().getStateChangedCondition().signalAll();
- // If the session expired we have to signal all conditions, because watches might have been removed and
- // there is no guarantee that those
- // conditions will be signaled at all after an Expired event
- // TODO PVo write a test for this
- if (event.getState() == KeeperState.Expired) {
- getEventLock().getZNodeEventCondition().signalAll();
- getEventLock().getDataChangedCondition().signalAll();
- // We also have to notify all listeners that something might have changed
- fireAllEvents();
- }
- }
- if (znodeChanged) {
- getEventLock().getZNodeEventCondition().signalAll();
- }
- if (dataChanged) {
- getEventLock().getDataChangedCondition().signalAll();
- }
- getEventLock().unlock();
- LOG.debug("Leaving process event");
- }
- }
- }
1. 再看看dubbo的consumer创建ZkClient的调用栈:
2. consumer的ZkClient注册childListener,等待节点内容改变的通知,对[/dubbo/com.zhang.HelloService/providers, /dubbo/com.zhang.HelloService/configurators, /dubbo/com.zhang.HelloService/routers]分别进行注册:
实际调用exists和getChildren方法,对应zk的stat path watch和ls path watch命令,即当/dubbo/com.zhang.HelloService/providers的值或者子节点改变时,客户端会收到通知:
- // ZkClient
- public List<String> watchForChilds(final String path) {
- if (_zookeeperEventThread != null && Thread.currentThread() == _zookeeperEventThread) {
- throw new IllegalArgumentException("Must not be done in the zookeeper event thread.");
- }
- return retryUntilConnected(new Callable<List<String>>() {
- @Override
- public List<String> call() throws Exception {
- exists(path, true);
- try {
- return getChildren(path, true);
- } catch (ZkNoNodeException e) {
- // ignore, the "exists" watch will listen for the parent node to appear
- }
- return null;
- }
- });
- }
- public <T> T retryUntilConnected(Callable<T> callable) throws ZkInterruptedException, IllegalArgumentException, ZkException, RuntimeException {
- if (_zookeeperEventThread != null && Thread.currentThread() == _zookeeperEventThread) {
- throw new IllegalArgumentException("Must not be done in the zookeeper event thread.");
- }
- while (true) {
- try {
- return callable.call();
- } catch (ConnectionLossException e) {
- // we give the event thread some time to update the status to 'Disconnected'
- Thread.yield();
- waitUntilConnected();
- } catch (SessionExpiredException e) {
- // we give the event thread some time to update the status to 'Expired'
- Thread.yield();
- waitUntilConnected();
- } catch (KeeperException e) {
- throw ZkException.create(e);
- } catch (InterruptedException e) {
- throw new ZkInterruptedException(e);
- } catch (Exception e) {
- throw ExceptionUtil.convertToRuntimeException(e);
- }
- }
- }
3. consumer收到通知,重新加watch
consumer的ZkClient收到通知后,会将通知包装成ZkEvent事件,发送给ZkEventThread,ZkEvent的run方法里重新地加上watch:
- private void fireChildChangedEvents(final String path, Set<IZkChildListener> childListeners) {
- try {
- // reinstall the watch
- for (final IZkChildListener listener : childListeners) {
- _eventThread.send(new ZkEvent("Children of " + path + " changed sent to " + listener) {
- @Override
- public void run() throws Exception {
- try {
- // if the node doesn't exist we should listen for the root node to reappear
- // 在函数内部,根据是否有listeners,判断加watch
- exists(path);
- List<String> children = getChildren(path);
- listener.handleChildChange(path, children);
- } catch (ZkNoNodeException e) {
- listener.handleChildChange(path, null);
- }
- }
- });
- }
- } catch (Exception e) {
- LOG.error("Failed to fire child changed event. Unable to getChildren. ", e);
- }
- }
4. 从ZkEvent的run方法进入,刷新配置:
ZkEventThread线程:
- class ZkEventThread extends Thread {
- private static final Logger LOG = Logger.getLogger(ZkEventThread.class);
- private BlockingQueue<ZkEvent> _events = new LinkedBlockingQueue<ZkEvent>();
- private static AtomicInteger _eventId = new AtomicInteger(0);
- static abstract class ZkEvent {
- private String _description;
- public ZkEvent(String description) {
- _description = description;
- }
- public abstract void run() throws Exception;
- @Override
- public String toString() {
- return "ZkEvent[" + _description + "]";
- }
- }
- ZkEventThread(String name) {
- setDaemon(true);
- setName("ZkClient-EventThread-" + getId() + "-" + name);
- }
- @Override
- public void run() {
- LOG.info("Starting ZkClient event thread.");
- try {
- while (!isInterrupted()) {
- ZkEvent zkEvent = _events.take();
- int eventId = _eventId.incrementAndGet();
- LOG.debug("Delivering event #" + eventId + " " + zkEvent);
- try {
- zkEvent.run();
- } catch (InterruptedException e) {
- interrupt();
- } catch (ZkInterruptedException e) {
- interrupt();
- } catch (Throwable e) {
- LOG.error("Error handling event " + zkEvent, e);
- }
- LOG.debug("Delivering event #" + eventId + " done");
- }
- } catch (InterruptedException e) {
- LOG.info("Terminate ZkClient event thread.");
- }
- }
- public void send(ZkEvent event) {
- if (!isInterrupted()) {
- LOG.debug("New event: " + event);
- _events.add(event);
- }
- }
- }
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