Shutdown.java :  » 6.0-JDK-Core » lang » java » lang » Java Open Source

Java Open Source » 6.0 JDK Core » lang 
lang » java » lang » Shutdown.java
/*
 * Copyright 1999-2005 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package java.lang;

import java.util.ArrayList;


/**
 * Package-private utility class containing data structures and logic
 * governing the virtual-machine shutdown sequence.
 *
 * @author   Mark Reinhold
 * @version  1.19, 07/05/05
 * @since    1.3
 */

class Shutdown {

    /* Shutdown state */
    private static final int RUNNING = 0;
    private static final int HOOKS = 1;
    private static final int FINALIZERS = 2;
    private static int state = RUNNING;

    /* Should we run all finalizers upon exit? */
    private static boolean runFinalizersOnExit = false;

    /* The set of registered, wrapped hooks, or null if there aren't any */
    private static ArrayList<Runnable> hooks = new ArrayList<Runnable>();

    /* The preceding static fields are protected by this lock */
    private static class Lock { };
    private static Object lock = new Lock();

    /* Lock object for the native halt method */
    private static Object haltLock = new Lock();

    /* Invoked by Runtime.runFinalizersOnExit */
    static void setRunFinalizersOnExit(boolean run) {
  synchronized (lock) {
      runFinalizersOnExit = run;
  }
    }


    /* Add a new shutdown hook.  Checks the shutdown state and the hook itself,
     * but does not do any security checks.
     */
    static void add(Runnable hook) {
  synchronized (lock) {
      if (state > RUNNING)
    throw new IllegalStateException("Shutdown in progress");

      hooks.add(hook);
  }
    }


    /* Remove a previously-registered hook.  Like the add method, this method
     * does not do any security checks.
     */
    static boolean remove(Runnable hook) {
  synchronized (lock) {
      if (state > RUNNING)
    throw new IllegalStateException("Shutdown in progress");
      if (hook == null) throw new NullPointerException();
      if (hooks == null) {
    return false;
      } else {
    return hooks.remove(hook);
      }
  }
    }


    /* Run all registered shutdown hooks
     */
    private static void runHooks() {
  /* We needn't bother acquiring the lock just to read the hooks field,
   * since the hooks can't be modified once shutdown is in progress
   */
  for (Runnable hook : hooks) {
      try {
    hook.run();
      } catch(Throwable t) { 
    if (t instanceof ThreadDeath) {
           ThreadDeath td = (ThreadDeath)t;
        throw td;
    } 
      }
  }
    }

    /* The halt method is synchronized on the halt lock
     * to avoid corruption of the delete-on-shutdown file list.
     * It invokes the true native halt method.
     */
    static void halt(int status) {
        synchronized (haltLock) {
            halt0(status);
        }
    }

    static native void halt0(int status);

    /* Wormhole for invoking java.lang.ref.Finalizer.runAllFinalizers */
    private static native void runAllFinalizers();


    /* The actual shutdown sequence is defined here.
     *
     * If it weren't for runFinalizersOnExit, this would be simple -- we'd just
     * run the hooks and then halt.  Instead we need to keep track of whether
     * we're running hooks or finalizers.  In the latter case a finalizer could
     * invoke exit(1) to cause immediate termination, while in the former case
     * any further invocations of exit(n), for any n, simply stall.  Note that
     * if on-exit finalizers are enabled they're run iff the shutdown is
     * initiated by an exit(0); they're never run on exit(n) for n != 0 or in
     * response to SIGINT, SIGTERM, etc.
     */
    private static void sequence() {
  synchronized (lock) {
      /* Guard against the possibility of a daemon thread invoking exit
       * after DestroyJavaVM initiates the shutdown sequence
       */
      if (state != HOOKS) return;
  }
  runHooks();
  boolean rfoe;
  synchronized (lock) {
      state = FINALIZERS;
      rfoe = runFinalizersOnExit;
  }
  if (rfoe) runAllFinalizers();
    }


    /* Invoked by Runtime.exit, which does all the security checks.
     * Also invoked by handlers for system-provided termination events,
     * which should pass a nonzero status code.
     */
    static void exit(int status) {
  boolean runMoreFinalizers = false;
  synchronized (lock) {
      if (status != 0) runFinalizersOnExit = false;
      switch (state) {
      case RUNNING:  /* Initiate shutdown */
    state = HOOKS;
    break;
      case HOOKS:    /* Stall and halt */
    break;
      case FINALIZERS:
    if (status != 0) {
        /* Halt immediately on nonzero status */
        halt(status);
    } else {
        /* Compatibility with old behavior:
         * Run more finalizers and then halt
         */
        runMoreFinalizers = runFinalizersOnExit;
    }
    break;
      }
  }
  if (runMoreFinalizers) {
      runAllFinalizers();
      halt(status);
  }
  synchronized (Shutdown.class) {
      /* Synchronize on the class object, causing any other thread
             * that attempts to initiate shutdown to stall indefinitely
       */
      sequence();
      halt(status);
  }
    }


    /* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon
     * thread has finished.  Unlike the exit method, this method does not
     * actually halt the VM.
     */
    static void shutdown() {
  synchronized (lock) {
      switch (state) {
      case RUNNING:  /* Initiate shutdown */
    state = HOOKS;
    break;
      case HOOKS:    /* Stall and then return */
      case FINALIZERS:
    break;
      }
  }
  synchronized (Shutdown.class) {
      sequence();
  }
    }

}
java2s.com  | Contact Us | Privacy Policy
Copyright 2009 - 12 Demo Source and Support. All rights reserved.
All other trademarks are property of their respective owners.