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 org.apache.harmony.luni.util;
19
20import java.lang.ref.SoftReference;
21import java.nio.CharBuffer;
22import java.nio.charset.Charset;
23import java.nio.charset.CharsetDecoder;
24import java.nio.charset.CharsetEncoder;
25
26/**
27 * The class extends the functionality of {@link java.lang.ThreadLocal} with
28 * possibility of discarding the thread local storage content when a heap is
29 * exhausted.
30 */
31public class ThreadLocalCache<T> {
32
33    private SoftReference<ThreadLocal<T>> storage = new SoftReference<ThreadLocal<T>>(
34            null);
35
36    private ThreadLocal<T> getThreadLocal() {
37        ThreadLocal<T> tls = storage.get();
38        if (tls == null) {
39            tls = new ThreadLocal<T>() {
40                public T initialValue() {
41                    return ThreadLocalCache.this.initialValue();
42                }
43            };
44            storage = new SoftReference<ThreadLocal<T>>(tls);
45        }
46        return tls;
47    }
48
49    /**
50     * Returns the initial value for the cache for the current thread.
51     */
52    protected T initialValue() {
53        return null;
54    }
55
56    /**
57     * Returns the thread local value of this object.
58     */
59    public T get() {
60        return getThreadLocal().get();
61    }
62
63    /**
64     * Sets the value of this variable for the current thread. Might be useful
65     * for expanding the thread local cache.
66     */
67    public void set(T value) {
68        getThreadLocal().set(value);
69    }
70
71    /**
72     * Discards the cache for all threads.
73     */
74    public void remove() {
75        storage.clear();
76    }
77
78    public static ThreadLocalCache<CharsetDecoder> utf8Decoder = new ThreadLocalCache<CharsetDecoder>() {
79        protected CharsetDecoder initialValue() {
80            return Charset.forName("UTF-8").newDecoder();
81        }
82    };
83
84    public static ThreadLocalCache<CharsetEncoder> utf8Encoder = new ThreadLocalCache<CharsetEncoder>() {
85        protected CharsetEncoder initialValue() {
86            return Charset.forName("UTF-8").newEncoder();
87        }
88    };
89
90    public static ThreadLocalCache<java.nio.ByteBuffer> byteBuffer = new ThreadLocalCache<java.nio.ByteBuffer>() {
91        protected java.nio.ByteBuffer initialValue() {
92            return java.nio.ByteBuffer.allocate(72); // >=
93            // Manifest.LINE_LENGTH_LIMIT
94        }
95    };
96
97    public static ThreadLocalCache<CharBuffer> charBuffer = new ThreadLocalCache<CharBuffer>() {
98        protected CharBuffer initialValue() {
99            return CharBuffer.allocate(72); // no specific requirement
100        }
101    };
102
103}
104