J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1998-2004 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.lang; |
| 27 | import java.lang.ref.*; |
| 28 | |
| 29 | /** |
| 30 | * This class extends <tt>ThreadLocal</tt> to provide inheritance of values |
| 31 | * from parent thread to child thread: when a child thread is created, the |
| 32 | * child receives initial values for all inheritable thread-local variables |
| 33 | * for which the parent has values. Normally the child's values will be |
| 34 | * identical to the parent's; however, the child's value can be made an |
| 35 | * arbitrary function of the parent's by overriding the <tt>childValue</tt> |
| 36 | * method in this class. |
| 37 | * |
| 38 | * <p>Inheritable thread-local variables are used in preference to |
| 39 | * ordinary thread-local variables when the per-thread-attribute being |
| 40 | * maintained in the variable (e.g., User ID, Transaction ID) must be |
| 41 | * automatically transmitted to any child threads that are created. |
| 42 | * |
| 43 | * @author Josh Bloch and Doug Lea |
| 44 | * @see ThreadLocal |
| 45 | * @since 1.2 |
| 46 | */ |
| 47 | |
| 48 | public class InheritableThreadLocal<T> extends ThreadLocal<T> { |
| 49 | /** |
| 50 | * Computes the child's initial value for this inheritable thread-local |
| 51 | * variable as a function of the parent's value at the time the child |
| 52 | * thread is created. This method is called from within the parent |
| 53 | * thread before the child is started. |
| 54 | * <p> |
| 55 | * This method merely returns its input argument, and should be overridden |
| 56 | * if a different behavior is desired. |
| 57 | * |
| 58 | * @param parentValue the parent thread's value |
| 59 | * @return the child thread's initial value |
| 60 | */ |
| 61 | protected T childValue(T parentValue) { |
| 62 | return parentValue; |
| 63 | } |
| 64 | |
| 65 | /** |
| 66 | * Get the map associated with a ThreadLocal. |
| 67 | * |
| 68 | * @param t the current thread |
| 69 | */ |
| 70 | ThreadLocalMap getMap(Thread t) { |
| 71 | return t.inheritableThreadLocals; |
| 72 | } |
| 73 | |
| 74 | /** |
| 75 | * Create the map associated with a ThreadLocal. |
| 76 | * |
| 77 | * @param t the current thread |
| 78 | * @param firstValue value for the initial entry of the table. |
| 79 | * @param map the map to store. |
| 80 | */ |
| 81 | void createMap(Thread t, T firstValue) { |
| 82 | t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue); |
| 83 | } |
| 84 | } |