content: /*
   * Copyright (c) 1998, 2012, Oracle and/or its affiliates. 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.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package java.lang;
  import java.lang.ref.*;
  
  /**
   * This class extends <tt>ThreadLocal</tt> to provide inheritance of values
   * from parent thread to child thread: when a child thread is created, the
   * child receives initial values for all inheritable thread-local variables
   * for which the parent has values.  Normally the child's values will be
   * identical to the parent's; however, the child's value can be made an
   * arbitrary function of the parent's by overriding the <tt>childValue</tt>
   * method in this class.
   *
   * <p>Inheritable thread-local variables are used in preference to
   * ordinary thread-local variables when the per-thread-attribute being
   * maintained in the variable (e.g., User ID, Transaction ID) must be
   * automatically transmitted to any child threads that are created.
   *
   * @author  Josh Bloch and Doug Lea
   * @see     ThreadLocal
   * @since   1.2
   */
  
  public class InheritableThreadLocal<T> extends ThreadLocal<T> {
      /**
       * Computes the child's initial value for this inheritable thread-local
       * variable as a function of the parent's value at the time the child
       * thread is created.  This method is called from within the parent
       * thread before the child is started.
       * <p>
       * This method merely returns its input argument, and should be overridden
       * if a different behavior is desired.
       *
       * @param parentValue the parent thread's value
       * @return the child thread's initial value
       */
      protected T childValue(T parentValue) {
          return parentValue;
      }
  
      /**
       * Get the map associated with a ThreadLocal.
       *
       * @param t the current thread
       */
      ThreadLocalMap getMap(Thread t) {
         return t.inheritableThreadLocals;
      }
  
      /**
       * Create the map associated with a ThreadLocal.
       *
       * @param t the current thread
       * @param firstValue value for the initial entry of the table.
       */
      void createMap(Thread t, T firstValue) {
          t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
      }
  }
  