InsiderAgent.java

/*
 * Copyright (C) 2011 Laurent Caillette
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation, either
 * version 3 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.novelang.outfit.shell.insider;


import java.lang.management.ManagementFactory;
import javax.management.MBeanServer;

/**
 * A Java agent that works in 2 ways:
 * <ul>
 *   <li>As pre-main at JVM startup for installing {@link Insider JMX bean}.
 *   <li>After JVM startup for executing a {@link Runtime#halt(int)} immediately.
 * </ul>
 * <p>
 * The JMX-based approach respects the Java Language Specification as it doesn't rely on
 * proprietary API. It is also faster.
 * <p>
 * The hot load of a Java agent relies on one of Sun's proprietary API. It makes sense
 * after a (lengthy) scan for JVMs on the local machine which have the
 * "tattoo" (see {@code org.novelang.outfit.shell.ShutdownTools.SHUTDOWN_TATTOO_PROPERTYNAME}).
 * But it's a full Java, multiplatform mean to shutdown a JVM.
 *
 *
 * @author Laurent Caillette
 */
@SuppressWarnings( { "UnusedDeclaration", "UseOfSystemOutOrSystemErr" } )
public class InsiderAgent {

    private InsiderAgent() { }

  /**
   * Called when launching a JVM with {@code -javaagent} option.
   * See <a href="http://java.sun.com/javase/6/docs/api/java/lang/instrument/package-summary.html">Java Instrumentation specification</a>.
   */
  public static void premain( final String arguments ) {
    final MBeanServer beanServer = ManagementFactory.getPlatformMBeanServer() ;
    final LocalInsider managedBean ;

    try {
      if( arguments != null
          && arguments.startsWith( Insider.MAXIMUM_HEARTBEATDELAY_PARAMETERNAME )
      ) out : {
        final String delayAsString = arguments.substring(
            Insider.MAXIMUM_HEARTBEATDELAY_PARAMETERNAME.length() ) ;
        final long delay;
        try {
          delay = Long.parseLong( delayAsString );
        } catch( NumberFormatException e ) {
          System.err.println( "Couldn't parse arguments '" + arguments + "', using defaults." ) ;
          managedBean = new LocalInsider() ;
          break out ;
        }
        managedBean = new LocalInsider( delay ) ;
      } else {
        managedBean = new LocalInsider() ;
      }
      beanServer.registerMBean( managedBean, Insider.NAME ) ;
    } catch( Exception e ) {
      // Checked exceptions in method signature prevent the JVM from loading the agent.
      throw new RuntimeException( e ) ;
    }
    System.out.println( "Loaded " + InsiderAgent.class.getName()
        + " inside " + managedBean.getVirtualMachineName() + "." ) ;
  }


  /**
   * Called when hot-loaded through
   * <a href="http://java.sun.com/javase/6/docs/jdk/api/attach/spec/com/sun/tools/attach/VirtualMachine.html#loadAgent%28java.lang.String,%20java.lang.String%29">Attach API</a>.
   */
  public static void agentmain( final String args ) {
    new Thread( new Runnable() {
      @Override
        public void run()
        {
            System.out.println( getClass().getName() + " halting JVM " + "..." ) ;
            Runtime.getRuntime().halt( 1 ) ;
        }
      } ).start() ;
  }
}