01 /*
02 * Copyright 1998-2004 Sun Microsystems, Inc. All Rights Reserved.
03 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
04 *
05 * This code is free software; you can redistribute it and/or modify it
06 * under the terms of the GNU General Public License version 2 only, as
07 * published by the Free Software Foundation. Sun designates this
08 * particular file as subject to the "Classpath" exception as provided
09 * 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
28 import java.lang.ref.*;
29
30 /**
31 * This class extends <tt>ThreadLocal</tt> to provide inheritance of values
32 * from parent thread to child thread: when a child thread is created, the
33 * child receives initial values for all inheritable thread-local variables
34 * for which the parent has values. Normally the child's values will be
35 * identical to the parent's; however, the child's value can be made an
36 * arbitrary function of the parent's by overriding the <tt>childValue</tt>
37 * method in this class.
38 *
39 * <p>Inheritable thread-local variables are used in preference to
40 * ordinary thread-local variables when the per-thread-attribute being
41 * maintained in the variable (e.g., User ID, Transaction ID) must be
42 * automatically transmitted to any child threads that are created.
43 *
44 * @author Josh Bloch and Doug Lea
45 * @version 1.28, 05/05/07
46 * @see ThreadLocal
47 * @since 1.2
48 */
49
50 public class InheritableThreadLocal<T> extends ThreadLocal<T> {
51 /**
52 * Computes the child's initial value for this inheritable thread-local
53 * variable as a function of the parent's value at the time the child
54 * thread is created. This method is called from within the parent
55 * thread before the child is started.
56 * <p>
57 * This method merely returns its input argument, and should be overridden
58 * if a different behavior is desired.
59 *
60 * @param parentValue the parent thread's value
61 * @return the child thread's initial value
62 */
63 protected T childValue(T parentValue) {
64 return parentValue;
65 }
66
67 /**
68 * Get the map associated with a ThreadLocal.
69 *
70 * @param t the current thread
71 */
72 ThreadLocalMap getMap(Thread t) {
73 return t.inheritableThreadLocals;
74 }
75
76 /**
77 * Create the map associated with a ThreadLocal.
78 *
79 * @param t the current thread
80 * @param firstValue value for the initial entry of the table.
81 * @param map the map to store.
82 */
83 void createMap(Thread t, T firstValue) {
84 t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
85 }
86 }
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