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 }
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