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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