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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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/*
 * Copyright (C) 2008 The Guava Authors
 *
 * 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. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base.internal;

import java.lang.ref.PhantomReference;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.CheckForNull;

/**
 * Thread that finalizes referents. All references should implement {@code
 * com.google.common.base.FinalizableReference}.
 *
 * 
While this class is public, we consider it to be *internal* and not part of our published API.
 * It is public so we can access it reflectively across class loaders in secure environments.
 *
 * 
This class can't depend on other Guava code. If we were to load this class in the same class
 * loader as the rest of Guava, this thread would keep an indirect strong reference to the class
 * loader and prevent it from being garbage collected. This poses a problem for environments where
 * you want to throw away the class loader. For example, dynamically reloading a web application or
 * unloading an OSGi bundle.
 *
 * 
{@code com.google.common.base.FinalizableReferenceQueue} loads this class in its own class
 * loader. That way, this class doesn't prevent the main class loader from getting garbage
 * collected, and this class can detect when the main class loader has been garbage collected and
 * stop itself.
 */
// no @ElementTypesAreNonNullByDefault for the reasons discussed above
public class Finalizer implements Runnable {

  private static final Logger logger = Logger.getLogger(Finalizer.class.getName());

  /** Name of FinalizableReference.class. */
  private static final String FINALIZABLE_REFERENCE = "com.google.common.base.FinalizableReference";

  /**
   * Starts the Finalizer thread. FinalizableReferenceQueue calls this method reflectively.
   *
   * @param finalizableReferenceClass FinalizableReference.class.
   * @param queue a reference queue that the thread will poll.
   * @param frqReference a phantom reference to the FinalizableReferenceQueue, which will be queued
   *     either when the FinalizableReferenceQueue is no longer referenced anywhere, or when its
   *     close() method is called.
   */
  public static void startFinalizer(
      Class finalizableReferenceClass,
      ReferenceQueue queue,
      PhantomReference frqReference) {
    /*
     * We use FinalizableReference.class for two things:
     *
     * 1) To invoke FinalizableReference.finalizeReferent()
     *
     * 2) To detect when FinalizableReference's class loader has to be garbage collected, at which
     * point, Finalizer can stop running
     */
    if (!finalizableReferenceClass.getName().equals(FINALIZABLE_REFERENCE)) {
      throw new IllegalArgumentException("Expected " + FINALIZABLE_REFERENCE + ".");
    }

    Finalizer finalizer = new Finalizer(finalizableReferenceClass, queue, frqReference);
    String threadName = Finalizer.class.getName();
    Thread thread = null;
    if (bigThreadConstructor != null) {
      try {
        boolean inheritThreadLocals = false;
        long defaultStackSize = 0;
        thread =
            bigThreadConstructor.newInstance(
                (ThreadGroup) null, finalizer, threadName, defaultStackSize, inheritThreadLocals);
      } catch (Throwable t) {
        logger.log(
            Level.INFO, "Failed to create a thread without inherited thread-local values", t);
      }
    }
    if (thread == null) {
      thread = new Thread((ThreadGroup) null, finalizer, threadName);
    }
    thread.setDaemon(true);

    try {
      if (inheritableThreadLocals != null) {
        inheritableThreadLocals.set(thread, null);
      }
    } catch (Throwable t) {
      logger.log(
          Level.INFO,
          "Failed to clear thread local values inherited by reference finalizer thread.",
          t);
    }

    thread.start();
  }

  private final WeakReference> finalizableReferenceClassReference;
  private final PhantomReference frqReference;
  private final ReferenceQueue queue;

  // By preference, we will use the Thread constructor that has an `inheritThreadLocals` parameter.
  // But before Java 9, our only way not to inherit ThreadLocals is to zap them after the thread
  // is created, by accessing a private field.
  @CheckForNull
  private static final Constructor bigThreadConstructor = getBigThreadConstructor();

  @CheckForNull
  private static final Field inheritableThreadLocals =
      (bigThreadConstructor == null) ? getInheritableThreadLocalsField() : null;

  /** Constructs a new finalizer thread. */
  private Finalizer(
      Class finalizableReferenceClass,
      ReferenceQueue queue,
      PhantomReference frqReference) {
    this.queue = queue;

    this.finalizableReferenceClassReference = new WeakReference<>(finalizableReferenceClass);

    // Keep track of the FRQ that started us so we know when to stop.
    this.frqReference = frqReference;
  }

  /** Loops continuously, pulling references off the queue and cleaning them up. */
  @SuppressWarnings("InfiniteLoopStatement")
  @Override
  public void run() {
    while (true) {
      try {
        if (!cleanUp(queue.remove())) {
          break;
        }
      } catch (InterruptedException e) {
        // ignore
      }
    }
  }

  /**
   * Cleans up the given reference and any other references already in the queue. Catches and logs
   * all throwables.
   *
   * @return true if the caller should continue to wait for more references to be added to the
   *     queue, false if the associated FinalizableReferenceQueue is no longer referenced.
   */
  private boolean cleanUp(Reference firstReference) {
    Method finalizeReferentMethod = getFinalizeReferentMethod();
    if (finalizeReferentMethod == null) {
      return false;
    }

    if (!finalizeReference(firstReference, finalizeReferentMethod)) {
      return false;
    }

    /*
     * Loop as long as we have references available so as not to waste CPU looking up the Method
     * over and over again.
     */
    while (true) {
      Reference furtherReference = queue.poll();
      if (furtherReference == null) {
        return true;
      }
      if (!finalizeReference(furtherReference, finalizeReferentMethod)) {
        return false;
      }
    }
  }

  /**
   * Cleans up the given reference. Catches and logs all throwables.
   *
   * @return true if the caller should continue to clean up references from the queue, false if the
   *     associated FinalizableReferenceQueue is no longer referenced.
   */
  private boolean finalizeReference(Reference reference, Method finalizeReferentMethod) {
    /*
     * This is for the benefit of phantom references. Weak and soft references will have already
     * been cleared by this point.
     */
    reference.clear();

    if (reference == frqReference) {
      /*
       * The client no longer has a reference to the FinalizableReferenceQueue. We can stop.
       */
      return false;
    }

    try {
      finalizeReferentMethod.invoke(reference);
    } catch (Throwable t) {
      logger.log(Level.SEVERE, "Error cleaning up after reference.", t);
    }
    return true;
  }

  /** Looks up FinalizableReference.finalizeReferent() method. */
  @CheckForNull
  private Method getFinalizeReferentMethod() {
    Class finalizableReferenceClass = finalizableReferenceClassReference.get();
    if (finalizableReferenceClass == null) {
      /*
       * FinalizableReference's class loader was reclaimed. While there's a chance that other
       * finalizable references could be enqueued subsequently (at which point the class loader
       * would be resurrected by virtue of us having a strong reference to it), we should pretty
       * much just shut down and make sure we don't keep it alive any longer than necessary.
       */
      return null;
    }
    try {
      return finalizableReferenceClass.getMethod("finalizeReferent");
    } catch (NoSuchMethodException e) {
      throw new AssertionError(e);
    }
  }

  @CheckForNull
  private static Field getInheritableThreadLocalsField() {
    try {
      Field inheritableThreadLocals = Thread.class.getDeclaredField("inheritableThreadLocals");
      inheritableThreadLocals.setAccessible(true);
      return inheritableThreadLocals;
    } catch (Throwable t) {
      logger.log(
          Level.INFO,
          "Couldn't access Thread.inheritableThreadLocals. Reference finalizer threads will "
              + "inherit thread local values.");
      return null;
    }
  }

  @CheckForNull
  private static Constructor getBigThreadConstructor() {
    try {
      return Thread.class.getConstructor(
          ThreadGroup.class, Runnable.class, String.class, long.class, boolean.class);
    } catch (Throwable t) {
      // Probably pre Java 9. We'll fall back to Thread.inheritableThreadLocals.
      return null;
    }
  }
}
    

    

    

            

    

            



    
    






    
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