Fix sonar issues in drools-pdp

Fix sonar issues about nested control loops in drools-pdp.
Rework1 build failed due to incorrect condition. fixing it
Fix checkstyle. Add modified copyright notice

Issue-ID: POLICY-1017
Change-Id: I21a4ad9399b1d234b8d5416ab0d595302a441f10
Signed-off-by: Krishnajinka <kris.jinka@samsung.com>

2 files changed, 536 insertions, 589 deletions

diff --git a/policy-core/src/main/java/org/onap/policy/drools/core/PolicyContainer.java b/policy-core/src/main/java/org/onap/policy/drools/core/PolicyContainer.java
index 1e8a2882..8a86a5c5 100644
--- a/policy-core/src/main/java/org/onap/policy/drools/core/PolicyContainer.java
+++ b/policy-core/src/main/java/org/onap/policy/drools/core/PolicyContainer.java
@@ -3,6 +3,7 @@
  * policy-core
  * ================================================================================
  * Copyright (C) 2017-2018 AT&T Intellectual Property. All rights reserved.
+ * Modifications Copyright (C) 2018 Samsung Electronics Co., Ltd.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -237,42 +238,44 @@ public class PolicyContainer implements Startable {
         synchronized (sessions) {
             logger.info("activatePolicySession:name :" + name);
             PolicySession session = sessions.get(name);
-            if (session == null) {
-                KieSession kieSession = null;
+            if (session != null) {
+                logger.info("activatePolicySession:session - " + session.getFullName() + " is returned.");
+                return session;
+            }
+            KieSession kieSession = null;
 
-                // loop through all of the features, and give each one
-                // a chance to create the 'KieSession'
-                for (PolicySessionFeatureAPI feature : PolicySessionFeatureAPI.impl.getList()) {
-                    try {
-                        if ((kieSession = feature.activatePolicySession(this, name, kieBaseName)) != null) {
-                            break;
-                        }
-                    } catch (Exception e) {
-                        logger.error(ERROR_STRING + feature.getClass().getName(), e);
+            // loop through all of the features, and give each one
+            // a chance to create the 'KieSession'
+            for (PolicySessionFeatureAPI feature : PolicySessionFeatureAPI.impl.getList()) {
+                try {
+                    if ((kieSession = feature.activatePolicySession(this, name, kieBaseName)) != null) {
+                        break;
                     }
+                } catch (Exception e) {
+                    logger.error(ERROR_STRING + feature.getClass().getName(), e);
                 }
+            }
 
-                // if none of the features created the session, create one now
-                if (kieSession == null) {
-                    kieSession = kieContainer.newKieSession(name);
-                }
+            // if none of the features created the session, create one now
+            if (kieSession == null) {
+                kieSession = kieContainer.newKieSession(name);
+            }
+
+            if (kieSession != null) {
+                // creation of 'KieSession' was successful - build
+                // a PolicySession
+                session = new PolicySession(name, this, kieSession);
+                sessions.put(name, session);
 
-                if (kieSession != null) {
-                    // creation of 'KieSession' was successful - build
-                    // a PolicySession
-                    session = new PolicySession(name, this, kieSession);
-                    sessions.put(name, session);
-
-                    // notify features
-                    for (PolicySessionFeatureAPI feature : PolicySessionFeatureAPI.impl.getList()) {
-                        try {
-                            feature.newPolicySession(session);
-                        } catch (Exception e) {
-                            logger.error(ERROR_STRING + feature.getClass().getName(), e);
-                        }
+                // notify features
+                for (PolicySessionFeatureAPI feature : PolicySessionFeatureAPI.impl.getList()) {
+                    try {
+                        feature.newPolicySession(session);
+                    } catch (Exception e) {
+                        logger.error(ERROR_STRING + feature.getClass().getName(), e);
                     }
-                    logger.info("activatePolicySession:new session was added in sessions with name " + name);
                 }
+                logger.info("activatePolicySession:new session was added in sessions with name " + name);
             }
             logger.info("activatePolicySession:session - " + (session == null ? "null" : session.getFullName())
                     + " is returned.");
@@ -497,21 +500,23 @@ public class PolicyContainer implements Startable {
      */
     @Override
     public synchronized boolean start() {
-        if (!isStarted) {
-            // This will create all 'PolicySession' instances specified in the
-            // 'kmodule.xml' file that don't exist yet
-            for (String kieBaseName : kieContainer.getKieBaseNames()) {
-                for (String kieSessionName : kieContainer.getKieSessionNamesInKieBase(kieBaseName)) {
-                    // if the 'PolicySession' does not currently exist, this method
-                    // call will attempt to create it
-                    PolicySession session = activatePolicySession(kieSessionName, kieBaseName);
-                    if (session != null) {
-                        session.startThread();
-                    }
+        if (isStarted) {
+            return true;
+        }
+
+        // This will create all 'PolicySession' instances specified in the
+        // 'kmodule.xml' file that don't exist yet
+        for (String kieBaseName : kieContainer.getKieBaseNames()) {
+            for (String kieSessionName : kieContainer.getKieSessionNamesInKieBase(kieBaseName)) {
+                // if the 'PolicySession' does not currently exist, this method
+                // call will attempt to create it
+                PolicySession session = activatePolicySession(kieSessionName, kieBaseName);
+                if (session != null) {
+                    session.startThread();
                 }
             }
-            isStarted = true;
         }
+        isStarted = true;
         return true;
     }
 
@@ -520,34 +525,37 @@ public class PolicyContainer implements Startable {
      */
     @Override
     public synchronized boolean stop() {
-        if (isStarted) {
-            Collection<PolicySession> localSessions;
+        if (!isStarted) {
+            return true;
+        }
 
-            synchronized (sessions) {
-                // local set containing all of the sessions
-                localSessions = new HashSet<>(sessions.values());
+        Collection<PolicySession> localSessions;
 
-                // clear the 'name->session' map in 'PolicyContainer'
-                sessions.clear();
-            }
-            for (PolicySession session : localSessions) {
-                // stop session thread
-                session.stopThread();
+        synchronized (sessions) {
+            // local set containing all of the sessions
+            localSessions = new HashSet<>(sessions.values());
 
-                // free KieSession resources
-                session.getKieSession().dispose();
+            // clear the 'name->session' map in 'PolicyContainer'
+            sessions.clear();
+        }
+        for (PolicySession session : localSessions) {
+            // stop session thread
+            session.stopThread();
 
-                // notify features
-                for (PolicySessionFeatureAPI feature : PolicySessionFeatureAPI.impl.getList()) {
-                    try {
-                        feature.disposeKieSession(session);
-                    } catch (Exception e) {
-                        logger.error(ERROR_STRING + feature.getClass().getName(), e);
-                    }
+            // free KieSession resources
+            session.getKieSession().dispose();
+
+            // notify features
+            for (PolicySessionFeatureAPI feature : PolicySessionFeatureAPI.impl.getList()) {
+                try {
+                    feature.disposeKieSession(session);
+                } catch (Exception e) {
+                    logger.error(ERROR_STRING + feature.getClass().getName(), e);
                 }
             }
-            isStarted = false;
         }
+        isStarted = false;
+
         return true;
     }
 
diff --git a/policy-core/src/main/java/org/onap/policy/drools/core/PolicySession.java b/policy-core/src/main/java/org/onap/policy/drools/core/PolicySession.java
index 431050f5..7646225e 100644
--- a/policy-core/src/main/java/org/onap/policy/drools/core/PolicySession.java
+++ b/policy-core/src/main/java/org/onap/policy/drools/core/PolicySession.java
@@ -3,13 +3,14 @@
  * policy-core
  * ================================================================================
  * Copyright (C) 2017-2018 AT&T Intellectual Property. All rights reserved.
+ * Modifications Copyright (C) 2018 Samsung Electronics Co., Ltd.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *      http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -43,534 +44,472 @@ import org.slf4j.LoggerFactory;
 
 /**
  * This class is a wrapper around 'KieSession', which adds the following:
- *
+ * <p>
  * 1) A thread running 'KieSession.fireUntilHalt()'
  * 2) Access to UEB
  * 3) Logging of events
  */
 public class PolicySession
-  implements AgendaEventListener, RuleRuntimeEventListener
-{
-	// get an instance of logger 
-  private static Logger  logger = LoggerFactory.getLogger(PolicySession.class);		
-  // name of the 'PolicySession' and associated 'KieSession'
-  private String name;
-
-  // the associated 'PolicyContainer', which may have additional
-  // 'PolicySession' instances in addition to this one
-  private PolicyContainer container;
-
-  // maps feature objects to per-PolicyContainer data
-  private ConcurrentHashMap<Object, Object> adjuncts =
-	new ConcurrentHashMap<>();
-
-  // associated 'KieSession' instance
-  private KieSession kieSession;
-
-  // if not 'null', this is the thread model processing the 'KieSession'
-  private ThreadModel threadModel = null;
-
-  // supports 'getCurrentSession()' method
-  private static ThreadLocal<PolicySession> policySess =
-	new ThreadLocal<>();
-
-  /**
-   * Internal constructor - create a 'PolicySession' instance
-   *
-   * @param name the name of this 'PolicySession' (and 'kieSession')
-   * @param container the 'PolicyContainer' instance containing this session
-   * @param kieSession the associated 'KieSession' instance
-   */
-  protected PolicySession(String name,
-						  PolicyContainer container, KieSession kieSession)
-  {
-	this.name = name;
-	this.container = container;
-	this.kieSession = kieSession;
-	kieSession.addEventListener((AgendaEventListener)this);
-	kieSession.addEventListener((RuleRuntimeEventListener)this);
-  }
-
-  /**
-   * @return the 'PolicyContainer' object containing this session
-   */
-  public PolicyContainer getPolicyContainer()
-  {
-	return container;
-  }
-
-  /**
-   * @return the associated 'KieSession' instance
-   */
-  public KieSession getKieSession()
-  {
-	return kieSession;
-  }
-
-  /**
-   * @return the local name of this session, which should either match the
-   * name specified in 'kmodule.xml' file associated with this session, or the
-   * name passed on the 'PolicyContainer.adoptKieSession' method.
-   */
-  public String getName()
-  {
-	return name;
-  }
-
-  /**
-   * @return the 'PolicyContainer' name, followed by ':', followed by the
-   * local name of the session. It should be useful in log messages.
-   */
-  public String getFullName()
-  {
-	return container.getName() + ":" + name;
-  }
-
-  /**
-   * If no 'ThreadModel' is currently running, this method will create one,
-   * and invoke it's 'start()' method. Features implementing
-   * 'PolicySessionFeatureAPI.selectThreadModel(...)' get a chance to create
-   * the ThreadModel instance.
-   */
-  public synchronized void startThread()
-  {
-	if (threadModel == null)
-	  {
-		// loop through all of the features, and give each one
-		// a chance to create the 'ThreadModel'
-		for (PolicySessionFeatureAPI feature :
-			   PolicySessionFeatureAPI.impl.getList())
-		  {
-			try
-			  {
-				if ((threadModel = feature.selectThreadModel(this)) != null)
-				  break;
-			  }
-			catch (Exception e)
-			  {
-				logger.error("ERROR: Feature API: "
-							 + feature.getClass().getName(), e);
-			  }
-		  }		
-		if (threadModel == null)
-		  {
-			// no feature created a ThreadModel -- select the default
-			threadModel = new DefaultThreadModel(this);
-		  }
-		logger.info("starting ThreadModel for session " + getFullName());
-		threadModel.start();
-	  }
-  }
-
-  /**
-   * If a 'ThreadModel' is currently running, this calls the 'stop()' method,
-   * and sets the 'threadModel' reference to 'null'.
-   */
-  public synchronized void stopThread()
-  {
-	if (threadModel != null)
-	  {
-		threadModel.stop();
-		threadModel = null;
-	  }
-  }
-
-  /**
-   * Notification that 'updateToVersion' was called on the container
-   */
-  void updated()
-  {
-	if (threadModel != null)
-	  {
-		// notify the 'ThreadModel', which may change one or more Thread names
-		threadModel.updated();
-	  }
-  }
-
-  /**
-   * Set this 'PolicySession' instance as the one associated with the
-   * currently-running thread.
-   */
-  public void setPolicySession()
-  {
-	// this sets a 'ThreadLocal' variable
-	policySess.set(this);
-  }
-
-  /**
-   * @return the 'PolicySession' instance associated with the current thread
-   *	(Note that this only works if the current thread is the one running
-   *	'kieSession.fireUntilHalt()'.)
-   */
-  public static PolicySession getCurrentSession()
-  {
-	return policySess.get();
-  }
-	
-  /**
-   * Fetch the adjunct object associated with a given feature
-   *
-   * @param object this is typically the singleton feature object that is
-   *	used as a key, but it might also be useful to use nested objects
-   *	within the feature as keys.
-   * @return a feature-specific object associated with the key, or 'null'
-   *	if it is not found.
-   */
-  public Object getAdjunct(Object object)
-  {
-	return adjuncts.get(object);
-  }
-
-  /**
-   * Store the adjunct object associated with a given feature
-   *
-   * @param object this is typically the singleton feature object that is
-   *	used as a key, but it might also be useful to use nested objects
-   *	within the feature as keys.
-   * @param value a feature-specific object associated with the key, or 'null'
-   *	if the feature-specific object should be removed
-   */
-  public void setAdjunct(Object object, Object value)
-  {
-	if (value == null)
-	  {
-		adjuncts.remove(object);
-	  }
-	else
-	  {
-		adjuncts.put(object, value);
-	  }
-  }
-
-  /***********************************/
-  /* 'AgendaEventListener' interface */
-  /***********************************/
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void afterMatchFired(AfterMatchFiredEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("afterMatchFired: " + getFullName()
-					 + ": AgendaEventListener.afterMatchFired(" + event + ")");
-	  }
-	PdpJmx.getInstance().ruleFired();
- }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void afterRuleFlowGroupActivated(RuleFlowGroupActivatedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-	logger.debug("afterRuleFlowGroupActivated: " + getFullName()
-				 + ": AgendaEventListener.afterRuleFlowGroupActivated("
-				 + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void afterRuleFlowGroupDeactivated
-	(RuleFlowGroupDeactivatedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("afterRuleFlowGroupDeactivated: " + getFullName()
-					 + ": AgendaEventListener.afterRuleFlowGroupDeactivated("
-					 + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void agendaGroupPopped(AgendaGroupPoppedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("agendaGroupPopped: " + getFullName()
-					 + ": AgendaEventListener.agendaGroupPopped("
-					 + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void agendaGroupPushed(AgendaGroupPushedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("agendaGroupPushed: " + getFullName()
-					 + ": AgendaEventListener.agendaGroupPushed("
-					 + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void beforeMatchFired(BeforeMatchFiredEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("beforeMatchFired: " + getFullName()
-					 + ": AgendaEventListener.beforeMatchFired("
-					 + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void beforeRuleFlowGroupActivated
-	(RuleFlowGroupActivatedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("beforeRuleFlowGroupActivated: " + getFullName()
-					 + ": AgendaEventListener.beforeRuleFlowGroupActivated("
-					 + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void beforeRuleFlowGroupDeactivated
-	(RuleFlowGroupDeactivatedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("beforeRuleFlowGroupDeactivated: " + getFullName()
-					 + ": AgendaEventListener.beforeRuleFlowGroupDeactivated("
-					 + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void matchCancelled(MatchCancelledEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("matchCancelled: " + getFullName()
-					 + ": AgendaEventListener.matchCancelled(" + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void matchCreated(MatchCreatedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("matchCreated: " + getFullName()
-					 + ": AgendaEventListener.matchCreated(" + event + ")");
-	  }
-  }
-
-  /****************************************/
-  /* 'RuleRuntimeEventListener' interface */
-  /****************************************/
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void objectDeleted(ObjectDeletedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("objectDeleted: " + getFullName()
-					 + ": AgendaEventListener.objectDeleted(" + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void objectInserted(ObjectInsertedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("objectInserted: " + getFullName()
-					 + ": AgendaEventListener.objectInserted(" + event + ")");
-	  }
-  }
-
-  /**
-   * {@inheritDoc}
-   */
-  @Override
-	public void objectUpdated(ObjectUpdatedEvent event)
-  {
-	if (logger.isDebugEnabled())
-	  {
-		logger.debug("objectUpdated: " + getFullName()
-					 + ": AgendaEventListener.objectUpdated(" + event + ")");
-	  }
-  }
-
-  /* ============================================================ */
-
-  /**
-   * This interface helps support the ability for features to choose the
-   * thread or threads that processes the 'KieSession'.
-   */
-  public interface ThreadModel
-  {
-	/**
-	 * Start the thread or threads that do the 'KieSession' processing
-	 */
-	public void start();
-
-	/**
-	 * Stop the thread or threads that do the 'KieSession' processing
-	 */
-	public void stop();
-
-	/**
-	 * This method is called to notify the running session that
-	 * 'KieContainer.updateToVersion(...)' has been called (meaning the
-	 * full name of this session has changed).
-	 */
-	public default void updated() {}
-  }
-
-  /* ============================================================ */
-
-  /**
-   * This 'ThreadModel' variant uses 'KieSession.fireUntilHalt()'.
-   */
-  public static class DefaultThreadModel implements Runnable,ThreadModel
-  {
-	// session associated with this persistent thread
-	PolicySession session;
-
-	// the session thread
-	Thread thread;
-
-	// controls whether the thread loops or terminates
-	volatile boolean repeat = true;
-
-	/**
-	 * Constructor - initialize 'session' and create thread
-	 *
-	 * @param session the 'PolicySession' instance
-	 */
-	public DefaultThreadModel(PolicySession session)
-	{
-	  this.session = session;
-	  thread = new Thread(this,getThreadName());
-	}
-
-	/**
-	 * @return the String to use as the thread name
-	 */
-	private String getThreadName()
-	{
-	  return "Session " + session.getFullName();
-	}
-
-	/***************************/
-	/* 'ThreadModel' interface */
-	/***************************/
-
-	/**
-	 * {@inheritDoc}
-	 */
-	@Override
-	  public void start()
-	{
-	  repeat = true;
-	  thread.start();
-	}
-
-	/**
-	 * {@inheritDoc}
-	 */
-	@Override
-	  public void stop()
-	{
-	  repeat = false;
-
-	  // this should cause the thread to exit		
-	  session.getKieSession().halt();
-	  try
-		{
-		  // wait up to 10 seconds for the thread to stop
-		  thread.join(10000);
-
-		  // one more interrupt, just in case the 'kieSession.halt()'
-		  // didn't work for some reason
-		  thread.interrupt();
-		}
-	  catch (Exception e)
-		{
-		  logger.error("stopThread in thread.join error", e);
-		}
-	}
-
-	/**
-	 * {@inheritDoc}
-	 */
-	@Override
-	  public void updated()
-	{
-	  // the container artifact has been updated -- adjust the thread name
-	  thread.setName(getThreadName());
-	}
-
-	/************************/
-	/* 'Runnable' interface */
-	/************************/
-
-	/**
-	 * {@inheritDoc}
-	 */
-	@Override
-	  public void run()
-	{
-	  // set thread local variable
-	  session.setPolicySession();
-
-	  // We want to continue looping, despite any exceptions that occur
-	  // while rules are fired.
-	  KieSession kieSession1 = session.getKieSession();
-	  while (repeat)
-		{
-		  try
-			{
-			  kieSession1.fireUntilHalt();
-
-			  // if we fall through, it means 'kieSession1.halt()' was called,
-			  // but this may be a result of 'KieScanner' doing an update
-			}
-		  catch (Exception | LinkageError e)
-			{
-			  logger.error("startThread error in kieSession1.fireUntilHalt", e);						
-			}
-		}
-	  logger.info("fireUntilHalt() returned");
-	}
-  }
+        implements AgendaEventListener, RuleRuntimeEventListener {
+    // get an instance of logger
+    private static Logger logger = LoggerFactory.getLogger(PolicySession.class);
+    // name of the 'PolicySession' and associated 'KieSession'
+    private String name;
+
+    // the associated 'PolicyContainer', which may have additional
+    // 'PolicySession' instances in addition to this one
+    private PolicyContainer container;
+
+    // maps feature objects to per-PolicyContainer data
+    private ConcurrentHashMap<Object, Object> adjuncts =
+            new ConcurrentHashMap<>();
+
+    // associated 'KieSession' instance
+    private KieSession kieSession;
+
+    // if not 'null', this is the thread model processing the 'KieSession'
+    private ThreadModel threadModel = null;
+
+    // supports 'getCurrentSession()' method
+    private static ThreadLocal<PolicySession> policySess =
+            new ThreadLocal<>();
+
+    /**
+     * Internal constructor - create a 'PolicySession' instance
+     *
+     * @param name       the name of this 'PolicySession' (and 'kieSession')
+     * @param container  the 'PolicyContainer' instance containing this session
+     * @param kieSession the associated 'KieSession' instance
+     */
+    protected PolicySession(String name,
+                            PolicyContainer container, KieSession kieSession) {
+        this.name = name;
+        this.container = container;
+        this.kieSession = kieSession;
+        kieSession.addEventListener((AgendaEventListener) this);
+        kieSession.addEventListener((RuleRuntimeEventListener) this);
+    }
+
+    /**
+     * @return the 'PolicyContainer' object containing this session
+     */
+    public PolicyContainer getPolicyContainer() {
+        return container;
+    }
+
+    /**
+     * @return the associated 'KieSession' instance
+     */
+    public KieSession getKieSession() {
+        return kieSession;
+    }
+
+    /**
+     * @return the local name of this session, which should either match the
+     * name specified in 'kmodule.xml' file associated with this session, or the
+     * name passed on the 'PolicyContainer.adoptKieSession' method.
+     */
+    public String getName() {
+        return name;
+    }
+
+    /**
+     * @return the 'PolicyContainer' name, followed by ':', followed by the
+     * local name of the session. It should be useful in log messages.
+     */
+    public String getFullName() {
+        return container.getName() + ":" + name;
+    }
+
+    /**
+     * If no 'ThreadModel' is currently running, this method will create one,
+     * and invoke it's 'start()' method. Features implementing
+     * 'PolicySessionFeatureAPI.selectThreadModel(...)' get a chance to create
+     * the ThreadModel instance.
+     */
+    public synchronized void startThread() {
+        if (threadModel != null) {
+            return;
+        }
+
+        // loop through all of the features, and give each one
+        // a chance to create the 'ThreadModel'
+        for (PolicySessionFeatureAPI feature :
+                PolicySessionFeatureAPI.impl.getList()) {
+            try {
+                if ((threadModel = feature.selectThreadModel(this)) != null)
+                    break;
+            } catch (Exception e) {
+                logger.error("ERROR: Feature API: "
+                        + feature.getClass().getName(), e);
+            }
+        }
+        if (threadModel == null) {
+            // no feature created a ThreadModel -- select the default
+            threadModel = new DefaultThreadModel(this);
+        }
+        logger.info("starting ThreadModel for session " + getFullName());
+        threadModel.start();
+    }
+
+    /**
+     * If a 'ThreadModel' is currently running, this calls the 'stop()' method,
+     * and sets the 'threadModel' reference to 'null'.
+     */
+    public synchronized void stopThread() {
+        if (threadModel != null) {
+            threadModel.stop();
+            threadModel = null;
+        }
+    }
+
+    /**
+     * Notification that 'updateToVersion' was called on the container
+     */
+    void updated() {
+        if (threadModel != null) {
+            // notify the 'ThreadModel', which may change one or more Thread names
+            threadModel.updated();
+        }
+    }
+
+    /**
+     * Set this 'PolicySession' instance as the one associated with the
+     * currently-running thread.
+     */
+    public void setPolicySession() {
+        // this sets a 'ThreadLocal' variable
+        policySess.set(this);
+    }
+
+    /**
+     * @return the 'PolicySession' instance associated with the current thread
+     * (Note that this only works if the current thread is the one running
+     * 'kieSession.fireUntilHalt()'.)
+     */
+    public static PolicySession getCurrentSession() {
+        return policySess.get();
+    }
+
+    /**
+     * Fetch the adjunct object associated with a given feature
+     *
+     * @param object this is typically the singleton feature object that is
+     *               used as a key, but it might also be useful to use nested objects
+     *               within the feature as keys.
+     * @return a feature-specific object associated with the key, or 'null'
+     * if it is not found.
+     */
+    public Object getAdjunct(Object object) {
+        return adjuncts.get(object);
+    }
+
+    /**
+     * Store the adjunct object associated with a given feature
+     *
+     * @param object this is typically the singleton feature object that is
+     *               used as a key, but it might also be useful to use nested objects
+     *               within the feature as keys.
+     * @param value  a feature-specific object associated with the key, or 'null'
+     *               if the feature-specific object should be removed
+     */
+    public void setAdjunct(Object object, Object value) {
+        if (value == null) {
+            adjuncts.remove(object);
+        } else {
+            adjuncts.put(object, value);
+        }
+    }
+
+    /***********************************/
+    /* 'AgendaEventListener' interface */
+    /***********************************/
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void afterMatchFired(AfterMatchFiredEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("afterMatchFired: " + getFullName()
+                    + ": AgendaEventListener.afterMatchFired(" + event + ")");
+        }
+        PdpJmx.getInstance().ruleFired();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void afterRuleFlowGroupActivated(RuleFlowGroupActivatedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("afterRuleFlowGroupActivated: " + getFullName()
+                    + ": AgendaEventListener.afterRuleFlowGroupActivated("
+                    + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void afterRuleFlowGroupDeactivated
+    (RuleFlowGroupDeactivatedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("afterRuleFlowGroupDeactivated: " + getFullName()
+                    + ": AgendaEventListener.afterRuleFlowGroupDeactivated("
+                    + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void agendaGroupPopped(AgendaGroupPoppedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("agendaGroupPopped: " + getFullName()
+                    + ": AgendaEventListener.agendaGroupPopped("
+                    + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void agendaGroupPushed(AgendaGroupPushedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("agendaGroupPushed: " + getFullName()
+                    + ": AgendaEventListener.agendaGroupPushed("
+                    + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void beforeMatchFired(BeforeMatchFiredEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("beforeMatchFired: " + getFullName()
+                    + ": AgendaEventListener.beforeMatchFired("
+                    + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void beforeRuleFlowGroupActivated
+    (RuleFlowGroupActivatedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("beforeRuleFlowGroupActivated: " + getFullName()
+                    + ": AgendaEventListener.beforeRuleFlowGroupActivated("
+                    + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void beforeRuleFlowGroupDeactivated
+    (RuleFlowGroupDeactivatedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("beforeRuleFlowGroupDeactivated: " + getFullName()
+                    + ": AgendaEventListener.beforeRuleFlowGroupDeactivated("
+                    + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void matchCancelled(MatchCancelledEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("matchCancelled: " + getFullName()
+                    + ": AgendaEventListener.matchCancelled(" + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void matchCreated(MatchCreatedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("matchCreated: " + getFullName()
+                    + ": AgendaEventListener.matchCreated(" + event + ")");
+        }
+    }
+
+    /****************************************/
+    /* 'RuleRuntimeEventListener' interface */
+    /****************************************/
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void objectDeleted(ObjectDeletedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("objectDeleted: " + getFullName()
+                    + ": AgendaEventListener.objectDeleted(" + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void objectInserted(ObjectInsertedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("objectInserted: " + getFullName()
+                    + ": AgendaEventListener.objectInserted(" + event + ")");
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void objectUpdated(ObjectUpdatedEvent event) {
+        if (logger.isDebugEnabled()) {
+            logger.debug("objectUpdated: " + getFullName()
+                    + ": AgendaEventListener.objectUpdated(" + event + ")");
+        }
+    }
+
+    /* ============================================================ */
+
+    /**
+     * This interface helps support the ability for features to choose the
+     * thread or threads that processes the 'KieSession'.
+     */
+    public interface ThreadModel {
+        /**
+         * Start the thread or threads that do the 'KieSession' processing
+         */
+        public void start();
+
+        /**
+         * Stop the thread or threads that do the 'KieSession' processing
+         */
+        public void stop();
+
+        /**
+         * This method is called to notify the running session that
+         * 'KieContainer.updateToVersion(...)' has been called (meaning the
+         * full name of this session has changed).
+         */
+        public default void updated() {
+        }
+    }
+
+    /* ============================================================ */
+
+    /**
+     * This 'ThreadModel' variant uses 'KieSession.fireUntilHalt()'.
+     */
+    public static class DefaultThreadModel implements Runnable, ThreadModel {
+        // session associated with this persistent thread
+        PolicySession session;
+
+        // the session thread
+        Thread thread;
+
+        // controls whether the thread loops or terminates
+        volatile boolean repeat = true;
+
+        /**
+         * Constructor - initialize 'session' and create thread
+         *
+         * @param session the 'PolicySession' instance
+         */
+        public DefaultThreadModel(PolicySession session) {
+            this.session = session;
+            thread = new Thread(this, getThreadName());
+        }
+
+        /**
+         * @return the String to use as the thread name
+         */
+        private String getThreadName() {
+            return "Session " + session.getFullName();
+        }
+
+        /***************************/
+        /* 'ThreadModel' interface */
+        /***************************/
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public void start() {
+            repeat = true;
+            thread.start();
+        }
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public void stop() {
+            repeat = false;
+
+            // this should cause the thread to exit
+            session.getKieSession().halt();
+            try {
+                // wait up to 10 seconds for the thread to stop
+                thread.join(10000);
+
+                // one more interrupt, just in case the 'kieSession.halt()'
+                // didn't work for some reason
+                thread.interrupt();
+            } catch (Exception e) {
+                logger.error("stopThread in thread.join error", e);
+            }
+        }
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public void updated() {
+            // the container artifact has been updated -- adjust the thread name
+            thread.setName(getThreadName());
+        }
+
+        /************************/
+        /* 'Runnable' interface */
+        /************************/
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public void run() {
+            // set thread local variable
+            session.setPolicySession();
+
+            // We want to continue looping, despite any exceptions that occur
+            // while rules are fired.
+            KieSession kieSession1 = session.getKieSession();
+            while (repeat) {
+                try {
+                    kieSession1.fireUntilHalt();
+
+                    // if we fall through, it means 'kieSession1.halt()' was called,
+                    // but this may be a result of 'KieScanner' doing an update
+                } catch (Exception | LinkageError e) {
+                    logger.error("startThread error in kieSession1.fireUntilHalt", e);
+                }
+            }
+            logger.info("fireUntilHalt() returned");
+        }
+    }
 }