HBASE-5918 Master will block forever at startup if root server dies between assigning root and assigning meta (Chunhui)

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1352161 13f79535-47bb-0310-9956-ffa450edef68

hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java

@@ -635,8 +635,7 @@ Server {
 
     // Make sure root and meta assigned before proceeding.
     if (!assignRootAndMeta(status)) return;
-    serverShutdownHandlerEnabled = true;
-    this.serverManager.expireDeadNotExpiredServers();
+    enableServerShutdownHandler();
 
     // Update meta with new HRI if required. i.e migrate all HRI with HTD to
     // HRI with out HTD in meta and update the status in ROOT. This must happen
@@ -719,6 +718,18 @@ Server {
     return new ServerManager(master, services);
   }
 
+  /**
+   * If ServerShutdownHandler is disabled, we enable it and expire those dead
+   * but not expired servers.
+   * @throws IOException
+   */
+  private void enableServerShutdownHandler() throws IOException {
+    if (!serverShutdownHandlerEnabled) {
+      serverShutdownHandlerEnabled = true;
+      this.serverManager.expireDeadNotExpiredServers();
+    }
+  }
+
   /**
    * Check <code>-ROOT-</code> and <code>.META.</code> are assigned.  If not,
    * assign them.
@@ -771,6 +782,7 @@ Server {
         splitLogAndExpireIfOnline(currentMetaServer);
       }
       assignmentManager.assignMeta();
+      enableServerShutdownHandler();
       this.catalogTracker.waitForMeta();
       // Above check waits for general meta availability but this does not
       // guarantee that the transition has completed