HADOOP-3963. Back port of HDFS-5257 - HDFS servers may start and stop external components through a plugin interface. Contributed by Brandon Li.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1388312 13f79535-47bb-0310-9956-ffa450edef68

src/hdfs/hdfs-default.xml

@@ -636,4 +636,18 @@ creations/deletions), or "all".</description>
   </description>
 </property>
 
+<property>
+  <name>dfs.datanode.plugins</name>
+  <value></value>
+  <description>Comma-separated list of datanode plug-ins to be activated.
+  </description>
+</property>
+
+<property>
+  <name>dfs.namenode.plugins</name>
+  <value></value>
+  <description>Comma-separated list of namenode plug-ins to be activated.
+  </description>
+</property>
+
 </configuration>

src/hdfs/org/apache/hadoop/hdfs/server/datanode/DataNode.java

@@ -128,6 +128,7 @@ import org.apache.hadoop.util.DiskChecker;
 import org.apache.hadoop.util.DiskChecker.DiskErrorException;
 import org.apache.hadoop.util.DiskChecker.DiskOutOfSpaceException;
 import org.apache.hadoop.util.ReflectionUtils;
+import org.apache.hadoop.util.ServicePlugin;
 import org.apache.hadoop.util.StringUtils;
 import org.apache.hadoop.util.VersionInfo;
 import org.mortbay.util.ajax.JSON;
@@ -251,6 +252,9 @@ public class DataNode extends Configured
   public DataBlockScanner blockScanner = null;
   public Daemon blockScannerThread = null;
   
+  /** Activated plug-ins. */
+  private List<ServicePlugin> plugins;
+  
   private static final Random R = new Random();
   
   public static final String DATA_DIR_KEY = "dfs.data.dir";
@@ -538,6 +542,16 @@ public class DataNode extends Configured
     dnRegistration.setIpcPort(ipcServer.getListenerAddress().getPort());
 
     LOG.info("dnRegistration = " + dnRegistration);
+    
+    plugins = conf.getInstances("dfs.datanode.plugins", ServicePlugin.class);
+    for (ServicePlugin p: plugins) {
+      try {
+        p.start(this);
+        LOG.info("Started plug-in " + p);
+      } catch (Throwable t) {
+        LOG.warn("ServicePlugin " + p + " could not be started", t);
+      }
+    }
   }
   
   private ObjectName mxBean = null;
@@ -800,6 +814,17 @@ public class DataNode extends Configured
    * Otherwise, deadlock might occur.
    */
   public void shutdown() {
+    if (plugins != null) {
+      for (ServicePlugin p : plugins) {
+        try {
+          p.stop();
+          LOG.info("Stopped plug-in " + p);
+        } catch (Throwable t) {
+          LOG.warn("ServicePlugin " + p + " could not be stopped", t);
+        }
+      }
+    }
+    
     this.unRegisterMXBean();
     if (infoServer != null) {
       try {

src/hdfs/org/apache/hadoop/hdfs/server/namenode/NameNode.java

@@ -89,6 +89,7 @@ import org.apache.hadoop.security.authorize.RefreshAuthorizationPolicyProtocol;
 import org.apache.hadoop.security.authorize.ServiceAuthorizationManager;
 import org.apache.hadoop.security.token.SecretManager.InvalidToken;
 import org.apache.hadoop.security.token.Token;
+import org.apache.hadoop.util.ServicePlugin;
 import org.apache.hadoop.util.StringUtils;
 
 /**********************************************************
@@ -178,6 +179,8 @@ public class NameNode implements ClientProtocol, DatanodeProtocol,
   private boolean stopRequested = false;
   /** Is service level authorization enabled? */
   private boolean serviceAuthEnabled = false;
+  /** Activated plug-ins. */
+  private List<ServicePlugin> plugins;
   
   /** Format a new filesystem.  Destroys any filesystem that may already
    * exist at this location.  **/
@@ -309,6 +312,15 @@ public class NameNode implements ClientProtocol, DatanodeProtocol,
       serviceRpcServer.start();      
     }
     startTrashEmptier(conf);
+    
+    plugins = conf.getInstances("dfs.namenode.plugins", ServicePlugin.class);
+    for (ServicePlugin p: plugins) {
+      try {
+        p.start(this);
+      } catch (Throwable t) {
+        LOG.warn("ServicePlugin " + p + " could not be started", t);
+      }
+    }
   }
 
   private void startTrashEmptier(Configuration conf) throws IOException {
@@ -551,6 +563,15 @@ public class NameNode implements ClientProtocol, DatanodeProtocol,
     if (stopRequested)
       return;
     stopRequested = true;
+    if (plugins != null) {
+      for (ServicePlugin p : plugins) {
+        try {
+          p.stop();
+        } catch (Throwable t) {
+          LOG.warn("ServicePlugin " + p + " could not be stopped", t);
+        }
+      }
+    }
     try {
       if (httpServer != null) httpServer.stop();
     } catch (Exception e) {