89 lines
3.4 KiB
Java
89 lines
3.4 KiB
Java
/*
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* Copyright (c) 1998, 2012, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.lang;
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import java.lang.ref.*;
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/**
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* This class extends {@code ThreadLocal} to provide inheritance of values
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* from parent thread to child thread: when a child thread is created, the
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* child receives initial values for all inheritable thread-local variables
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* for which the parent has values. Normally the child's values will be
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* identical to the parent's; however, the child's value can be made an
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* arbitrary function of the parent's by overriding the {@code childValue}
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* method in this class.
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*
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* <p>Inheritable thread-local variables are used in preference to
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* ordinary thread-local variables when the per-thread-attribute being
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* maintained in the variable (e.g., User ID, Transaction ID) must be
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* automatically transmitted to any child threads that are created.
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*
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* <p>Note: During the creation of a new {@link
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* Thread#Thread(ThreadGroup,Runnable,String,long,boolean) thread}, it is
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* possible to <i>opt out</i> of receiving initial values for inheritable
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* thread-local variables.
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*
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* @author Josh Bloch and Doug Lea
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* @see ThreadLocal
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* @since 1.2
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*/
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public class InheritableThreadLocal<T> extends ThreadLocal<T> {
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/**
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* Computes the child's initial value for this inheritable thread-local
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* variable as a function of the parent's value at the time the child
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* thread is created. This method is called from within the parent
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* thread before the child is started.
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* <p>
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* This method merely returns its input argument, and should be overridden
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* if a different behavior is desired.
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*
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* @param parentValue the parent thread's value
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* @return the child thread's initial value
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*/
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protected T childValue(T parentValue) {
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return parentValue;
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}
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/**
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* Get the map associated with a ThreadLocal.
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*
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* @param t the current thread
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*/
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ThreadLocalMap getMap(Thread t) {
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return t.inheritableThreadLocals;
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}
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/**
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* Create the map associated with a ThreadLocal.
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*
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* @param t the current thread
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* @param firstValue value for the initial entry of the table.
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*/
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void createMap(Thread t, T firstValue) {
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t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
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}
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}
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