我正在使用Apache Curator图书馆在Zookeeper上进行领导选举.我的应用程序代码部署在各种机器中,我需要从一台机器执行我的代码,这就是为什么我在zookeeper上进行领导选举,以便我可以检查我是否是领导者,然后执行此代码.
以下是我的LeaderElectionExecutor类,它确保每个应用程序都有一个策展人实例
public class LeaderElectionExecutor {
private ZookeeperClient zookClient;
private static final String LEADER_NODE = "/testleader";
private static class Holder {
static final LeaderElectionExecutor INSTANCE = new LeaderElectionExecutor();
}
public static LeaderElectionExecutor getInstance() {
return Holder.INSTANCE;
}
private LeaderElectionExecutor() {
try {
String hostname = Utils.getHostName();
String nodes = "host1:2181,host2:2181;
zookClient = new ZookeeperClient(nodes,LEADER_NODE,hostname);
zookClient.start();
// added sleep specifically for the leader to get selected
// since I cannot call isLeader method immediately after starting the latch
TimeUnit.MINUTES.sleep(1);
} catch (Exception ex) {
// logging error
System.exit(1);
}
}
public ZookeeperClient getZookClient() {
return zookClient;
}
}
以下是我的ZookeeperClient代码 –
// can this class be improved in any ways?
public class ZookeeperClient {
private CuratorFramework client;
private String latchPath;
private String id;
private LeaderLatch leaderLatch;
public ZookeeperClient(String connString,String latchPath,String id) {
client = CuratorFrameworkFactory.newClient(connString,new ExponentialBackoffRetry(1000,Integer.MAX_VALUE));
this.id = id;
this.latchPath = latchPath;
}
public void start() throws Exception {
client.start();
leaderLatch = new LeaderLatch(client,latchPath,id);
leaderLatch.start();
}
public boolean isLeader() {
return leaderLatch.hasLeadership();
}
public Participant currentLeader() throws Exception {
return leaderLatch.getLeader();
}
public void close() throws IOException {
leaderLatch.close();
client.close();
}
public CuratorFramework getClient() {
return client;
}
public String getLatchPath() {
return latchPath;
}
public String getId() {
return id;
}
public LeaderLatch getLeaderLatch() {
return leaderLatch;
}
}
现在在我的应用程序中,我正在使用这样的代码 –
public void method01() {
ZookeeperClient zookClient = LeaderElectionExecutor.getInstance().getZookClient();
if (zookClient.isLeader()) {
// do something
}
}
public void method02() {
ZookeeperClient zookClient = LeaderElectionExecutor.getInstance().getZookClient();
if (zookClient.isLeader()) {
// do something
}
}
问题陈述：-
在策展人库中 – 调用isLeader()在启动锁定后立即不起作用.领导选择需要时间.而且由于这个原因,我已经在我的LeaderElectionExecutor代码中添加了1分钟的睡眠,但是我觉得这不是正确的方法.
有没有更好的办法呢？记住这一点,我需要一种方法来检查我是否是领导者,然后执行这段代码.我不能在一个方法中做所有事情,所以我需要调用来自不同类和方法的isLeader方法来检查我是否是领导者,然后执行这段代码.
我正在使用Zookeeper 3.4.5和Curator 1.7.1版本.
解决方法
一旦我解决了一个非常类似于你的问题.这是我怎么做到的.
首先,我有我的对象由Spring管理.所以我有一个LeaderLatch可以通过容器注入.使用LeaderLatch的组件之一是LeadershipWatcher,一个Runnable接口的实现,将领导事件发送到其他组件.这些最后一个组件是我命名为LeadershipObserver的接口的实现. LeadershipWatcher的实现主要是如下代码：
@Component
public class LeadershipWatcher implements Runnable {
private final LeaderLatch leaderLatch;
private final Collection<LeadershipObserver> leadershipObservers;
/* constructor with @Inject */
@Override
public void run() {
try {
leaderLatch.await();
for (LeadershipObserver observer : leadershipObservers) {
observer.granted();
}
} catch (InterruptedException e) {
for (LeadershipObserver observer : leadershipObservers) {
observer.interrupted();
}
}
}
}
由于这只是一个草图,我建议您加强此代码,也许应用命令模式调用观察者,甚至将观察者提交到线程池,如果他们的作业阻塞或长时间运行cpu密集型任务.
