1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/rt/emul/compact/src/main/java/java/lang/ThreadLocal.java Thu Sep 12 12:26:23 2013 +0200
1.3 @@ -0,0 +1,157 @@
1.4 +/*
1.5 + * Copyright (c) 1997, 2007, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation. Oracle designates this
1.11 + * particular file as subject to the "Classpath" exception as provided
1.12 + * by Oracle in the LICENSE file that accompanied this code.
1.13 + *
1.14 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.15 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.16 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.17 + * version 2 for more details (a copy is included in the LICENSE file that
1.18 + * accompanied this code).
1.19 + *
1.20 + * You should have received a copy of the GNU General Public License version
1.21 + * 2 along with this work; if not, write to the Free Software Foundation,
1.22 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.23 + *
1.24 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.25 + * or visit www.oracle.com if you need additional information or have any
1.26 + * questions.
1.27 + */
1.28 +
1.29 +package java.lang;
1.30 +
1.31 +/**
1.32 + * This class provides thread-local variables. These variables differ from
1.33 + * their normal counterparts in that each thread that accesses one (via its
1.34 + * <tt>get</tt> or <tt>set</tt> method) has its own, independently initialized
1.35 + * copy of the variable. <tt>ThreadLocal</tt> instances are typically private
1.36 + * static fields in classes that wish to associate state with a thread (e.g.,
1.37 + * a user ID or Transaction ID).
1.38 + *
1.39 + * <p>For example, the class below generates unique identifiers local to each
1.40 + * thread.
1.41 + * A thread's id is assigned the first time it invokes <tt>ThreadId.get()</tt>
1.42 + * and remains unchanged on subsequent calls.
1.43 + * <pre>
1.44 + * import java.util.concurrent.atomic.AtomicInteger;
1.45 + *
1.46 + * public class ThreadId {
1.47 + * // Atomic integer containing the next thread ID to be assigned
1.48 + * private static final AtomicInteger nextId = new AtomicInteger(0);
1.49 + *
1.50 + * // Thread local variable containing each thread's ID
1.51 + * private static final ThreadLocal<Integer> threadId =
1.52 + * new ThreadLocal<Integer>() {
1.53 + * @Override protected Integer initialValue() {
1.54 + * return nextId.getAndIncrement();
1.55 + * }
1.56 + * };
1.57 + *
1.58 + * // Returns the current thread's unique ID, assigning it if necessary
1.59 + * public static int get() {
1.60 + * return threadId.get();
1.61 + * }
1.62 + * }
1.63 + * </pre>
1.64 + * <p>Each thread holds an implicit reference to its copy of a thread-local
1.65 + * variable as long as the thread is alive and the <tt>ThreadLocal</tt>
1.66 + * instance is accessible; after a thread goes away, all of its copies of
1.67 + * thread-local instances are subject to garbage collection (unless other
1.68 + * references to these copies exist).
1.69 + *
1.70 + * @author Josh Bloch and Doug Lea
1.71 + * @since 1.2
1.72 + */
1.73 +public class ThreadLocal<T> {
1.74 + private static final Object NONE = new Object();
1.75 + private Object value = NONE;
1.76 +
1.77 + /**
1.78 + * Returns the current thread's "initial value" for this
1.79 + * thread-local variable. This method will be invoked the first
1.80 + * time a thread accesses the variable with the {@link #get}
1.81 + * method, unless the thread previously invoked the {@link #set}
1.82 + * method, in which case the <tt>initialValue</tt> method will not
1.83 + * be invoked for the thread. Normally, this method is invoked at
1.84 + * most once per thread, but it may be invoked again in case of
1.85 + * subsequent invocations of {@link #remove} followed by {@link #get}.
1.86 + *
1.87 + * <p>This implementation simply returns <tt>null</tt>; if the
1.88 + * programmer desires thread-local variables to have an initial
1.89 + * value other than <tt>null</tt>, <tt>ThreadLocal</tt> must be
1.90 + * subclassed, and this method overridden. Typically, an
1.91 + * anonymous inner class will be used.
1.92 + *
1.93 + * @return the initial value for this thread-local
1.94 + */
1.95 + protected T initialValue() {
1.96 + return null;
1.97 + }
1.98 +
1.99 + /**
1.100 + * Creates a thread local variable.
1.101 + */
1.102 + public ThreadLocal() {
1.103 + }
1.104 +
1.105 + /**
1.106 + * Returns the value in the current thread's copy of this
1.107 + * thread-local variable. If the variable has no value for the
1.108 + * current thread, it is first initialized to the value returned
1.109 + * by an invocation of the {@link #initialValue} method.
1.110 + *
1.111 + * @return the current thread's value of this thread-local
1.112 + */
1.113 + public T get() {
1.114 + if (value == NONE) {
1.115 + return setInitialValue();
1.116 + } else {
1.117 + return (T)value;
1.118 + }
1.119 + }
1.120 +
1.121 + /**
1.122 + * Variant of set() to establish initialValue. Used instead
1.123 + * of set() in case user has overridden the set() method.
1.124 + *
1.125 + * @return the initial value
1.126 + */
1.127 + private T setInitialValue() {
1.128 + T v = initialValue();
1.129 + this.value = v;
1.130 + return v;
1.131 + }
1.132 +
1.133 + /**
1.134 + * Sets the current thread's copy of this thread-local variable
1.135 + * to the specified value. Most subclasses will have no need to
1.136 + * override this method, relying solely on the {@link #initialValue}
1.137 + * method to set the values of thread-locals.
1.138 + *
1.139 + * @param value the value to be stored in the current thread's copy of
1.140 + * this thread-local.
1.141 + */
1.142 + public void set(T value) {
1.143 + this.value = value;
1.144 + }
1.145 +
1.146 + /**
1.147 + * Removes the current thread's value for this thread-local
1.148 + * variable. If this thread-local variable is subsequently
1.149 + * {@linkplain #get read} by the current thread, its value will be
1.150 + * reinitialized by invoking its {@link #initialValue} method,
1.151 + * unless its value is {@linkplain #set set} by the current thread
1.152 + * in the interim. This may result in multiple invocations of the
1.153 + * <tt>initialValue</tt> method in the current thread.
1.154 + *
1.155 + * @since 1.5
1.156 + */
1.157 + public void remove() {
1.158 + this.value = NONE;
1.159 + }
1.160 +}