1/*
2 *  Licensed to the Apache Software Foundation (ASF) under one or more
3 *  contributor license agreements.  See the NOTICE file distributed with
4 *  this work for additional information regarding copyright ownership.
5 *  The ASF licenses this file to You under the Apache License, Version 2.0
6 *  (the "License"); you may not use this file except in compliance with
7 *  the License.  You may obtain a copy of the License at
8 *
9 *     http://www.apache.org/licenses/LICENSE-2.0
10 *
11 *  Unless required by applicable law or agreed to in writing, software
12 *  distributed under the License is distributed on an "AS IS" BASIS,
13 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 *  See the License for the specific language governing permissions and
15 *  limitations under the License.
16 */
17
18package java.lang;
19
20
21/**
22 * A thread-local variable whose value is passed from parent to child thread. By
23 * default, the value of an inheritable thread-local variable of a child thread
24 * is initialized with the value of the parent thread's variable at thread
25 * creation time. However, subclasses may override {code #childValue(Object)}
26 * to provide an arbitrary function for passing the value of a parent's
27 * thread-local variable to the child's thread-local variable.
28 *
29 * @see java.lang.Thread
30 * @see java.lang.ThreadLocal
31 */
32public class InheritableThreadLocal<T> extends ThreadLocal<T> {
33
34    /**
35     * Creates a new inheritable thread-local variable.
36     */
37    public InheritableThreadLocal() {
38    }
39
40    /**
41     * Computes the initial value of this thread-local variable for the child
42     * thread given the parent thread's value. Called from the parent thread when
43     * creating a child thread. The default implementation returns the parent
44     * thread's value.
45     *
46     * @param parentValue the value of the variable in the parent thread.
47     * @return the initial value of the variable for the child thread.
48     */
49    protected T childValue(T parentValue) {
50        return parentValue;
51    }
52
53    @Override
54    Values values(Thread current) {
55        return current.inheritableValues;
56    }
57
58    @Override
59    Values initializeValues(Thread current) {
60        return current.inheritableValues = new Values();
61    }
62}
63