92aaa24628
From-SVN: r49104
179 lines
6.0 KiB
Java
179 lines
6.0 KiB
Java
/* java.lang.InheritableThreadLocal
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Copyright (C) 2000, 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.lang;
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import java.util.Iterator;
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import java.util.HashSet;
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import java.util.Map;
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import java.util.Set;
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import java.util.WeakHashMap;
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/**
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* ThreadLocal whose value is inherited by child Threads.
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* The value of the InheritableThreadLocal associated with the (parent) Thread
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* on the moment that it creates a new (child) Thread is set as the value that
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* is associated with the new (child) Thread.
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* <p>
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* It is possible to make the value associated with the child Thread a function
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* of the value that is associated with the parent Thread by overriding the
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* <code>childValue()</code> method.
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*
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* @since 1.2
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* @author Mark Wielaard (mark@klomp.org)
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*/
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public class InheritableThreadLocal extends ThreadLocal {
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/**
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* Maps Threads to a Set of InheritableThreadLocals
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* (the heritage of that Thread).
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* Uses a WeakHashMap so if the Thread is garbage collected the reference
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* to that Set disappears.
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* Both <code>AddToHeritage</code> access and modify it so they have to
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* synchronize on the threadMap when they do.
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*/
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private static Map threadMap = new WeakHashMap();
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/**
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* Creates a new InheritableThreadLocal that has no values associated
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* with it yet.
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*/
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public InheritableThreadLocal() {
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super();
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}
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/**
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* Determines the value associated with a newly created child Thread
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* as a function of the value associated with the currently executing
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* (parent) Thread.
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* <p>
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* The default implementation just returns the parentValue.
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*/
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protected Object childValue(Object parentValue) {
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return parentValue;
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}
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/**
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* Adds this <code>InheritableThreadLocal</code> to the heritage of the
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* current Thread and returns the value of the <code>ThreadLocal</code>
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* for the Thread. The value will be either the last value that the
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* current Thread has set, or the childValue of the last value that the
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* parent Thread set before the current Thread was created, or the
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* initialValue of the <code>ThreadLocal</code>.
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*
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* @see ThreadLocal#get()
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*/
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public Object get() {
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addToHeritage();
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return super.get();
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}
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/**
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* Adds this <code>InheritableThreadLocal</code> to the heritage of the
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* current Thread and sets the value of the <code>ThreadLocal</code>
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* for the Thread.
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*
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* @see ThreadLocal#set(Object)
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*/
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public void set(Object value) {
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addToHeritage();
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super.set(value);
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}
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/**
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* Adds this <code>InheritableThreadLocal</code> to the heritage
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* of the current Thread.
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*/
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private void addToHeritage() {
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Thread currentThread = Thread.currentThread();
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Set heritage;
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synchronized(threadMap) {
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heritage = (Set)threadMap.get(currentThread);
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}
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// Note that we don't have to synchronize on the heritage Set
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// since only this Thread (or the parent Thread when creating
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// the heritage) ever modifies it.
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if (heritage == null) {
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heritage = new HashSet();
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synchronized(threadMap) {
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threadMap.put(currentThread, heritage);
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}
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}
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if (!heritage.contains(this)) {
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heritage.add(this);
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}
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}
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/**
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* Generates the childValues of all <code>InheritableThreadLocal</code>s
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* that are in the heritage of the current Thread for the newly created
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* childThread.
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* Should be called from the contructor of java.lang.Thread.
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*/
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static void newChildThread(Thread childThread) {
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// The currentThread is the parent of the new thread
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Thread parentThread = Thread.currentThread();
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// Inherit all the InheritableThreadLocals of the parent thread
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Set heritage;
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synchronized(threadMap) {
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heritage = (Set)threadMap.get(parentThread);
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}
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// Note that we don't have to synchronize on the heritage Set
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// since only this Thread (or the parent Thread when creating
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// the heritage) ever modifies it.
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if (heritage != null) {
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synchronized(threadMap) {
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threadMap.put(childThread, new HashSet(heritage));
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}
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// And constructs all the new child values
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// (has to be done now that we are executing in the parentThread)
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Iterator it = heritage.iterator();
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while (it.hasNext()) {
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InheritableThreadLocal local =
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(InheritableThreadLocal) it.next();
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// Note that the parentValue cannot be null
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// If it was it would not be in the heritage
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Object parentValue = local.get(parentThread).getValue();
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Object childValue = local.childValue(parentValue);
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ThreadLocal.Value v = new ThreadLocal.Value(childValue);
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local.set(childThread, v);
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}
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}
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}
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}
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