plugins/org.eclipse.epp.wizard/src/org/eclipse/epp/wizard/internal/ModelCache.java

/*******************************************************************************
 * Copyright (c) 2008 Innoopract Informationssysteme GmbH.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     Innoopract Informationssysteme GmbH - initial API and implementation
 ******************************************************************************/
package org.eclipse.epp.wizard.internal;

import java.io.File;
import java.net.URL;

import org.apache.log4j.Logger;
import org.eclipse.epp.wizard.model.EPPModel;

/**
 * Cache for model data, so it does not have to be parsed for each session, but
 * still is up to date.
 * 
 * @author mwoelker
 */
public class ModelCache {

  private static final String EPPMODEL_XML_FILENAME = "eppmodel.xml";
  static Logger logger = Logger.getLogger( ModelCache.class );
  private Object LOCK = new Object();
  private Configuration configuration;
  private EPPModel model;
  private long UPDATE_CHECK_IN_SEC = 10;
  private long UPDATE_INTERVAL_IN_SEC = 60 * 60; // hourly
  private long ERROR_UPDATE_INTERVAL_IN_SEC = 1;
  private long lastUpdate = 0;
  /**
   * This updater Thread runs in the background to keep model information
   * up-to-date during the lifetime of the application Three intervals are used:
   * UPDATE_CHECK_IN_SEC - used for checking the modification date on the
   * eppmodel.xml file, model is reload if changed UPDATE_INTERVAL_IN_SEC -
   * model is reloaded in this interval, regardless of modification timestamps,
   * picks up changes in the upstream P2 Metadata repositories
   * ERROR_UPDATE_INTERVAL_IN_SEC - This interval kicks in if the update fails,
   * e.g. when the network is down
   * 
   * @author mwoelker
   */
  protected class ModelUpdater implements Runnable {

    public void run() {
      File modelDirectory = configuration.getModelDirectory();
      File modelXML = new File( modelDirectory, EPPMODEL_XML_FILENAME );
      long lastModified = 0;
      while( true ) {
        try {
          long newLastModified = modelXML.lastModified();
          if( lastModified != newLastModified ) {
            reload();
            lastModified = newLastModified;
          }
          if( lastUpdate + ( UPDATE_INTERVAL_IN_SEC * 1000 ) < System.currentTimeMillis() )
          {
            reload();
          }
          sleep( UPDATE_CHECK_IN_SEC );
        } catch( Throwable t ) {
          logger.error( "Error updating model", t );
          sleep( ERROR_UPDATE_INTERVAL_IN_SEC );
        }
      }
    }

    /**
     * reloads the model and updates the internal member variable
     * 
     * @throws Exception
     */
    private void reload() throws Exception {
      EPPModel tempModel = loadModel();
      synchronized( LOCK ) {
        model = tempModel;
        lastUpdate = System.currentTimeMillis();
      }
      logger.info( "Updated model" );
    }

    private void sleep( long timeInSec ) {
      try {
        Thread.sleep( timeInSec * 1000 );
      } catch( InterruptedException e ) {
        Thread.currentThread().interrupt();
      }
    }
  }

  public ModelCache( Configuration configuration ) {
    super();
    this.configuration = configuration;
    Thread updateThread = new Thread( new ModelUpdater() );
    updateThread.setName( "EPP Model updater" );
    updateThread.setDaemon( true );
    updateThread.start();
  }

  public EPPModel getModel() throws Exception {
    synchronized( LOCK ) {
      if( model == null ) {
        model = loadModel();
      }
      return model;
    }
  }

  protected EPPModel loadModel() throws Exception {
    File modelDirectory = configuration.getModelDirectory();
    File modelXML = new File( modelDirectory, EPPMODEL_XML_FILENAME );
    EPPModel model = null;
    model = EPPModel.read( modelXML.toURI().toURL(),
                           new URL( configuration.getEppMetadataRepository() ) );
    return model;
  }
}