leader 选举

haha174 · Mar 21, 2020 · 1174717 · 1174717
1 parent 7e891aa
commit 1174717
Showing 1 changed file with 43 additions and 3 deletions.
diff --git a/...pes-election/src/main/java/org/apache/zookeeper/recipes/leader/LeaderElectionSupport.java b/...pes-election/src/main/java/org/apache/zookeeper/recipes/leader/LeaderElectionSupport.java
@@ -89,16 +89,31 @@
 public class LeaderElectionSupport implements Watcher {
 
     private static final Logger LOG = LoggerFactory.getLogger(LeaderElectionSupport.class);
-
+    /**
+     * zookeeper client
+     */
     private ZooKeeper zooKeeper;
-
+    /**
+     * 状态
+     */
     private State state;
     private Set<LeaderElectionAware> listeners;
-
+    /**
+     * 选举的根节点地址
+     */
     private String rootNodeName;
+    /**
+     * leader 对象类
+     */
     private LeaderOffer leaderOffer;
+    /**
+     * 当前的主机名
+     */
     private String hostName;
 
+    /**
+     * 构造函数 构造一个对象线程安全的set 集合 存放监听事件
+     */
     public LeaderElectionSupport() {
         state = State.STOP;
         listeners = Collections.synchronizedSet(new HashSet<>());
@@ -116,8 +131,12 @@ public LeaderElectionSupport() {
      * listeners.
      * </p>
      */
+    /**
+     *选举的开始方法
+     */
     public synchronized void start() {
         state = State.START;
+        // 广播选举开始
         dispatchEvent(EventType.START);
 
         LOG.info("Starting leader election support");
@@ -144,6 +163,9 @@ public synchronized void start() {
      * Stops all election services, revokes any outstanding leader offers, and
      * disconnects from ZooKeeper.
      */
+    /**
+     * 停止选举并删除 对应节点
+     */
     public synchronized void stop() {
         state = State.STOP;
         dispatchEvent(EventType.STOP_START);
@@ -162,6 +184,11 @@ public synchronized void stop() {
         dispatchEvent(EventType.STOP_COMPLETE);
     }
 
+    /**
+     *  在root 目录下创建节点
+     * @throws KeeperException
+     * @throws InterruptedException
+     */
     private void makeOffer() throws KeeperException, InterruptedException {
         state = State.OFFER;
         dispatchEvent(EventType.OFFER_START);
@@ -173,6 +200,7 @@ private void makeOffer() throws KeeperException, InterruptedException {
             hostnameBytes = hostName.getBytes();
             newLeaderOffer.setNodePath(zooKeeper.create(rootNodeName + "/" + "n_",
                                                         hostnameBytes, ZooDefs.Ids.OPEN_ACL_UNSAFE,
+                                                        // 零时节点
                                                         CreateMode.EPHEMERAL_SEQUENTIAL));
             leaderOffer = newLeaderOffer;
         }
@@ -185,6 +213,12 @@ private synchronized LeaderOffer getLeaderOffer() {
         return leaderOffer;
     }
 
+    /**
+     *
+     * 选出最小序号的文件 对应的机器就是leader
+     * @throws KeeperException
+     * @throws InterruptedException
+     */
     private void determineElectionStatus() throws KeeperException, InterruptedException {
 
         state = State.DETERMINE;
@@ -213,8 +247,10 @@ private void determineElectionStatus() throws KeeperException, InterruptedExcept
                 dispatchEvent(EventType.DETERMINE_COMPLETE);
 
                 if (i == 0) {
+                    // 最小的那个变成leader
                     becomeLeader();
                 } else {
+                    // 其他的是非leader
                     becomeReady(leaderOffers.get(i - 1));
                 }
 
@@ -236,6 +272,10 @@ private void becomeReady(LeaderOffer neighborLeaderOffer)
          * Make sure to pass an explicit Watcher because we could be sharing this
          * zooKeeper instance with someone else.
          */
+        /**
+         *
+         * 进行watch，监视上一个节点 如果上一个节点删除了 就重新掉用determineElectionStatus
+         */
         Stat stat = zooKeeper.exists(neighborLeaderOffer.getNodePath(), this);
 
         if (stat != null) {