package org.apache.commons.jcs.auxiliary;
   
   /*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.locks.Condition;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReentrantLock;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  /**
   * Used to monitor and repair any failed connection for the lateral cache service. By default the
   * monitor operates in a failure driven mode. That is, it goes into a wait state until there is an
   * error. Upon the notification of a connection error, the monitor changes to operate in a time
   * driven mode. That is, it attempts to recover the connections on a periodic basis. When all failed
   * connections are restored, it changes back to the failure driven mode.
   */
  public abstract class AbstractAuxiliaryCacheMonitor extends Thread
  {
      /** The logger */
      protected final Log log = LogFactory.getLog( this.getClass() );
  
      /** How long to wait between runs */
      protected static long idlePeriod = 20 * 1000;
  
      /**
       * Must make sure AbstractAuxiliaryCacheMonitor is started before any error can be detected!
       */
      protected AtomicBoolean allright = new AtomicBoolean(true);
  
      /**
       * shutdown flag
       */
      private AtomicBoolean shutdown = new AtomicBoolean(false);
  
      /** Synchronization helper lock */
      private Lock lock = new ReentrantLock();
  
      /** Synchronization helper condition */
      private Condition trigger = lock.newCondition();
  
      /**
       * Constructor
       *
       * @param name the thread name
       */
      public AbstractAuxiliaryCacheMonitor(String name)
      {
          super(name);
      }
  
      /**
       * Configures the idle period between repairs.
       * <p>
       * @param idlePeriod The new idlePeriod value
       */
      public static void setIdlePeriod( long idlePeriod )
      {
          if ( idlePeriod > AbstractAuxiliaryCacheMonitor.idlePeriod )
          {
              AbstractAuxiliaryCacheMonitor.idlePeriod = idlePeriod;
          }
      }
  
      /**
       * Notifies the cache monitor that an error occurred, and kicks off the error recovery process.
       */
      public void notifyError()
      {
          if (allright.compareAndSet(true, false))
          {
              signalTrigger();
          }
      }
  
      /**
       * Notifies the cache monitor that the service shall shut down
       */
      public void notifyShutdown()
      {
         if (shutdown.compareAndSet(false, true))
         {
             signalTrigger();
         }
     }
 
     // Trigger continuation of loop
     private void signalTrigger()
     {
         try
         {
             lock.lock();
             trigger.signal();
         }
         finally
         {
             lock.unlock();
         }
     }
 
     /**
      * Clean up all resources before shutdown
      */
     protected abstract void dispose();
 
     /**
      * do actual work
      */
     protected abstract void doWork();
 
     /**
      * Main processing method for the AbstractAuxiliaryCacheMonitor object
      */
     @Override
     public void run()
     {
         do
         {
             if ( log.isDebugEnabled() )
             {
                 if ( allright.get() )
                 {
                     log.debug( "ERROR DRIVEN MODE: allright = true, cache monitor will wait for an error." );
                 }
                 else
                 {
                     log.debug( "ERROR DRIVEN MODE: allright = false cache monitor running." );
                 }
             }
 
             if ( allright.get() )
             {
                 // Failure driven mode.
                 try
                 {
                     lock.lock();
                     trigger.await();
                     // wake up only if there is an error.
                 }
                 catch ( InterruptedException ignore )
                 {
                     //no op, this is expected
                 }
                 finally
                 {
                     lock.unlock();
                 }
             }
 
             // check for requested shutdown
             if ( shutdown.get() )
             {
                 log.info( "Shutting down cache monitor" );
                 dispose();
                 return;
             }
 
             // The "allright" flag must be false here.
             // Simply presume we can fix all the errors until proven otherwise.
             allright.set(true);
 
             if ( log.isDebugEnabled() )
             {
                 log.debug( "Cache monitor running." );
             }
 
             doWork();
 
             try
             {
                 // don't want to sleep after waking from an error
                 // run immediately and sleep here.
                 if ( log.isDebugEnabled() )
                 {
                     log.debug( "Cache monitor sleeping for " + idlePeriod + " between runs." );
                 }
 
                 Thread.sleep( idlePeriod );
             }
             catch ( InterruptedException ex )
             {
                 // ignore;
             }
         }
         while ( true );
     }
 }