MAPREDUCE-3909

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1294219 13f79535-47bb-0310-9956-ffa450edef68

hadoop-mapreduce-project/CHANGES.txt

@@ -56,6 +56,8 @@ Trunk (unreleased changes)
 
     MAPREDUCE-2944. Improve checking of input for JobClient.displayTasks() (XieXianshan via harsh)
 
+    MAPREDUCE-3909 Javadoc the Service interfaces (stevel)
+
   BUG FIXES
 
     MAPREDUCE-3757. [Rumen] Fixed Rumen Folder to adjust shuffleFinished and

hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/service/AbstractService.java

@@ -28,14 +28,37 @@ import org.apache.hadoop.conf.Configuration;
 public abstract class AbstractService implements Service {
 
   private static final Log LOG = LogFactory.getLog(AbstractService.class);
-  
+
+  /**
+   * Service state: initially {@link STATE#NOTINITED}.
+   */
   private STATE state = STATE.NOTINITED;
+
+  /**
+   * Service name.
+   */
   private final String name;
+  /**
+   * Service start time. Will be zero until the service is started.
+   */
   private long startTime;
+
+  /**
+   * The configuration. Will be null until the service is initialized.
+   */
   private Configuration config;
+
+  /**
+   * List of state change listeners; it is final to ensure
+   * that it will never be null.
+   */
   private List<ServiceStateChangeListener> listeners =
     new ArrayList<ServiceStateChangeListener>();
 
+  /**
+   * Construct the service.
+   * @param name service name
+   */
   public AbstractService(String name) {
     this.name = name;
   }
@@ -45,6 +68,11 @@ public abstract class AbstractService implements Service {
     return state;
   }
 
+  /**
+   * {@inheritDoc}
+   * @throws IllegalStateException if the current service state does not permit
+   * this action
+   */
   @Override
   public synchronized void init(Configuration conf) {
     ensureCurrentState(STATE.NOTINITED);
@@ -53,6 +81,11 @@ public abstract class AbstractService implements Service {
     LOG.info("Service:" + getName() + " is inited.");
   }
 
+  /**
+   * {@inheritDoc}
+   * @throws IllegalStateException if the current service state does not permit
+   * this action
+   */
   @Override
   public synchronized void start() {
     startTime = System.currentTimeMillis();
@@ -61,6 +94,11 @@ public abstract class AbstractService implements Service {
     LOG.info("Service:" + getName() + " is started.");
   }
 
+  /**
+   * {@inheritDoc}
+   * @throws IllegalStateException if the current service state does not permit
+   * this action
+   */
   @Override
   public synchronized void stop() {
     if (state == STATE.STOPPED ||
@@ -100,6 +138,12 @@ public abstract class AbstractService implements Service {
     return startTime;
   }
 
+  /**
+   * Verify that that a service is in a given state.
+   * @param currentState the desired state
+   * @throws IllegalStateException if the service state is different from
+   * the desired state
+   */
   private void ensureCurrentState(STATE currentState) {
     if (state != currentState) {
       throw new IllegalStateException("For this operation, current State must " +
@@ -107,6 +151,14 @@ public abstract class AbstractService implements Service {
     }
   }
 
+  /**
+   * Change to a new state and notify all listeners.
+   * This is a private method that is only invoked from synchronized methods,
+   * which avoid having to clone the listener list. It does imply that
+   * the state change listener methods should be short lived, as they
+   * will delay the state transition.
+   * @param newState new service state
+   */
   private void changeState(STATE newState) {
     state = newState;
     //notify listeners

hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/service/Service.java

@@ -25,21 +25,87 @@ import org.apache.hadoop.conf.Configuration;
  */
 public interface Service {
 
+  /**
+   * Service states
+   */
   public enum STATE {
+    /** Constructed but not initialized */
     NOTINITED,
+
+    /** Initialized but not started or stopped */
     INITED,
+
+    /** started and not stopped */
     STARTED,
-    STOPPED;
+
+    /** stopped. No further state transitions are permitted */
+    STOPPED
   }
 
+  /**
+   * Initialize the service.
+   *
+   * The transition must be from {@link STATE#NOTINITED} to {@link STATE#INITED}
+   * unless the operation failed and an exception was raised.
+   * @param config the configuration of the service
+   */
   void init(Configuration config);
+
+
+  /**
+   * Start the service.
+   *
+   * The transition should be from {@link STATE#INITED} to {@link STATE#STARTED}
+   * unless the operation failed and an exception was raised.
+   */
+
   void start();
+
+  /**
+   * Stop the service.
+   *
+   * This operation must be designed to complete regardless of the initial state
+   * of the service, including the state of all its internal fields.
+   */
   void stop();
+
+  /**
+   * Register an instance of the service state change events.
+   * @param listener a new listener
+   */
   void register(ServiceStateChangeListener listener);
+
+  /**
+   * Unregister a previously instance of the service state change events.
+   * @param listener the listener to unregister.
+   */
   void unregister(ServiceStateChangeListener listener);
 
+  /**
+   * Get the name of this service.
+   * @return the service name
+   */
   String getName();
+
+  /**
+   * Get the configuration of this service.
+   * This is normally not a clone and may be manipulated, though there are no
+   * guarantees as to what the consequences of such actions may be
+   * @return the current configuration, unless a specific implentation chooses
+   * otherwise.
+   */
   Configuration getConfig();
+
+  /**
+   * Get the current service state
+   * @return the state of the service
+   */
   STATE getServiceState();
+
+  /**
+   * Get the service start time
+   * @return the start time of the service. This will be zero if the service
+   * has not yet been started.
+   */
   long getStartTime();
 }

hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/service/ServiceStateChangeListener.java

@@ -23,6 +23,23 @@ package org.apache.hadoop.yarn.service;
  */
 public interface ServiceStateChangeListener {
 
+  /**
+   * Callback to notify of a state change. The service will already
+   * have changed state before this callback is invoked.
+   *
+   * This operation is invoked on the thread that initiated the state change,
+   * while the service itself in in a sychronized section.
+   * <ol>
+   *   <li>Any long-lived operation here will prevent the service state
+   *   change from completing in a timely manner.</li>
+   *   <li>If another thread is somehow invoked from the listener, and
+   *   that thread invokes the methods of the service (including
+   *   subclass-specific methods), there is a risk of a deadlock.</li>
+   * </ol>
+   *
+   *
+   * @param service the service that has changed.
+   */
   void stateChanged(Service service);
 
 }