|
| 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 | + |
| 18 | +package com.alibaba.dubbo.common.threadlocal; |
| 19 | + |
| 20 | +import java.util.Collections; |
| 21 | +import java.util.IdentityHashMap; |
| 22 | +import java.util.Set; |
| 23 | + |
| 24 | +/** |
| 25 | + * InternalThreadLocal |
| 26 | + * A special variant of {@link ThreadLocal} that yields higher access performance when accessed from a |
| 27 | + * {@link InternalThread}. |
| 28 | + * <p></p> |
| 29 | + * Internally, a {@link InternalThread} uses a constant index in an array, instead of using hash code and hash table, |
| 30 | + * to look for a variable. Although seemingly very subtle, it yields slight performance advantage over using a hash |
| 31 | + * table, and it is useful when accessed frequently. |
| 32 | + * <p></p> |
| 33 | + * This design is learning from {@see io.netty.util.concurrent.FastThreadLocal} which is in Netty. |
| 34 | + */ |
| 35 | +public class InternalThreadLocal<V> { |
| 36 | + |
| 37 | + private static final int variablesToRemoveIndex = InternalThreadLocalMap.nextVariableIndex(); |
| 38 | + |
| 39 | + private final int index; |
| 40 | + |
| 41 | + public InternalThreadLocal() { |
| 42 | + index = InternalThreadLocalMap.nextVariableIndex(); |
| 43 | + } |
| 44 | + |
| 45 | + /** |
| 46 | + * Removes all {@link InternalThreadLocal} variables bound to the current thread. This operation is useful when you |
| 47 | + * are in a container environment, and you don't want to leave the thread local variables in the threads you do not |
| 48 | + * manage. |
| 49 | + */ |
| 50 | + @SuppressWarnings("unchecked") |
| 51 | + public static void removeAll() { |
| 52 | + InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.getIfSet(); |
| 53 | + if (threadLocalMap == null) { |
| 54 | + return; |
| 55 | + } |
| 56 | + |
| 57 | + try { |
| 58 | + Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex); |
| 59 | + if (v != null && v != InternalThreadLocalMap.UNSET) { |
| 60 | + Set<InternalThreadLocal<?>> variablesToRemove = (Set<InternalThreadLocal<?>>) v; |
| 61 | + for (InternalThreadLocal<?> tlv : variablesToRemove) { |
| 62 | + tlv.remove(threadLocalMap); |
| 63 | + } |
| 64 | + } |
| 65 | + } finally { |
| 66 | + InternalThreadLocalMap.remove(); |
| 67 | + } |
| 68 | + } |
| 69 | + |
| 70 | + /** |
| 71 | + * Returns the number of thread local variables bound to the current thread. |
| 72 | + */ |
| 73 | + public static int size() { |
| 74 | + InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.getIfSet(); |
| 75 | + if (threadLocalMap == null) { |
| 76 | + return 0; |
| 77 | + } else { |
| 78 | + return threadLocalMap.size(); |
| 79 | + } |
| 80 | + } |
| 81 | + |
| 82 | + public static void destroy() { |
| 83 | + InternalThreadLocalMap.destroy(); |
| 84 | + } |
| 85 | + |
| 86 | + @SuppressWarnings("unchecked") |
| 87 | + private static void addToVariablesToRemove(InternalThreadLocalMap threadLocalMap, InternalThreadLocal<?> variable) { |
| 88 | + Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex); |
| 89 | + Set<InternalThreadLocal<?>> variablesToRemove; |
| 90 | + if (v == InternalThreadLocalMap.UNSET || v == null) { |
| 91 | + variablesToRemove = Collections.newSetFromMap(new IdentityHashMap<InternalThreadLocal<?>, Boolean>()); |
| 92 | + threadLocalMap.setIndexedVariable(variablesToRemoveIndex, variablesToRemove); |
| 93 | + } else { |
| 94 | + variablesToRemove = (Set<InternalThreadLocal<?>>) v; |
| 95 | + } |
| 96 | + |
| 97 | + variablesToRemove.add(variable); |
| 98 | + } |
| 99 | + |
| 100 | + @SuppressWarnings("unchecked") |
| 101 | + private static void removeFromVariablesToRemove(InternalThreadLocalMap threadLocalMap, InternalThreadLocal<?> variable) { |
| 102 | + |
| 103 | + Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex); |
| 104 | + |
| 105 | + if (v == InternalThreadLocalMap.UNSET || v == null) { |
| 106 | + return; |
| 107 | + } |
| 108 | + |
| 109 | + Set<InternalThreadLocal<?>> variablesToRemove = (Set<InternalThreadLocal<?>>) v; |
| 110 | + variablesToRemove.remove(variable); |
| 111 | + } |
| 112 | + |
| 113 | + /** |
| 114 | + * Returns the current value for the current thread |
| 115 | + */ |
| 116 | + @SuppressWarnings("unchecked") |
| 117 | + public final V get() { |
| 118 | + InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.get(); |
| 119 | + Object v = threadLocalMap.indexedVariable(index); |
| 120 | + if (v != InternalThreadLocalMap.UNSET) { |
| 121 | + return (V) v; |
| 122 | + } |
| 123 | + |
| 124 | + return initialize(threadLocalMap); |
| 125 | + } |
| 126 | + |
| 127 | + private V initialize(InternalThreadLocalMap threadLocalMap) { |
| 128 | + V v = null; |
| 129 | + try { |
| 130 | + v = initialValue(); |
| 131 | + } catch (Exception e) { |
| 132 | + throw new RuntimeException(e); |
| 133 | + } |
| 134 | + |
| 135 | + threadLocalMap.setIndexedVariable(index, v); |
| 136 | + addToVariablesToRemove(threadLocalMap, this); |
| 137 | + return v; |
| 138 | + } |
| 139 | + |
| 140 | + /** |
| 141 | + * Sets the value for the current thread. |
| 142 | + */ |
| 143 | + public final void set(V value) { |
| 144 | + if (value == null || value == InternalThreadLocalMap.UNSET) { |
| 145 | + remove(); |
| 146 | + } else { |
| 147 | + InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.get(); |
| 148 | + if (threadLocalMap.setIndexedVariable(index, value)) { |
| 149 | + addToVariablesToRemove(threadLocalMap, this); |
| 150 | + } |
| 151 | + } |
| 152 | + } |
| 153 | + |
| 154 | + /** |
| 155 | + * Sets the value to uninitialized; a proceeding call to get() will trigger a call to initialValue(). |
| 156 | + */ |
| 157 | + @SuppressWarnings("unchecked") |
| 158 | + public final void remove() { |
| 159 | + remove(InternalThreadLocalMap.getIfSet()); |
| 160 | + } |
| 161 | + |
| 162 | + /** |
| 163 | + * Sets the value to uninitialized for the specified thread local map; |
| 164 | + * a proceeding call to get() will trigger a call to initialValue(). |
| 165 | + * The specified thread local map must be for the current thread. |
| 166 | + */ |
| 167 | + @SuppressWarnings("unchecked") |
| 168 | + public final void remove(InternalThreadLocalMap threadLocalMap) { |
| 169 | + if (threadLocalMap == null) { |
| 170 | + return; |
| 171 | + } |
| 172 | + |
| 173 | + Object v = threadLocalMap.removeIndexedVariable(index); |
| 174 | + removeFromVariablesToRemove(threadLocalMap, this); |
| 175 | + |
| 176 | + if (v != InternalThreadLocalMap.UNSET) { |
| 177 | + try { |
| 178 | + onRemoval((V) v); |
| 179 | + } catch (Exception e) { |
| 180 | + throw new RuntimeException(e); |
| 181 | + } |
| 182 | + } |
| 183 | + } |
| 184 | + |
| 185 | + /** |
| 186 | + * Returns the initial value for this thread-local variable. |
| 187 | + */ |
| 188 | + protected V initialValue() throws Exception { |
| 189 | + return null; |
| 190 | + } |
| 191 | + |
| 192 | + /** |
| 193 | + * Invoked when this thread local variable is removed by {@link #remove()}. |
| 194 | + */ |
| 195 | + protected void onRemoval(@SuppressWarnings("unused") V value) throws Exception { |
| 196 | + } |
| 197 | +} |
0 commit comments