| /* InheritableThreadLocal -- a ThreadLocal which inherits values across threads |
| Copyright (C) 2000, 2001, 2002, 2003, 2005 Free Software Foundation, Inc. |
| |
| This file is part of GNU Classpath. |
| |
| GNU Classpath is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2, or (at your option) |
| any later version. |
| |
| GNU Classpath is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GNU Classpath; see the file COPYING. If not, write to the |
| Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 02111-1307 USA. |
| |
| Linking this library statically or dynamically with other modules is |
| making a combined work based on this library. Thus, the terms and |
| conditions of the GNU General Public License cover the whole |
| combination. |
| |
| As a special exception, the copyright holders of this library give you |
| permission to link this library with independent modules to produce an |
| executable, regardless of the license terms of these independent |
| modules, and to copy and distribute the resulting executable under |
| terms of your choice, provided that you also meet, for each linked |
| independent module, the terms and conditions of the license of that |
| module. An independent module is a module which is not derived from |
| or based on this library. If you modify this library, you may extend |
| this exception to your version of the library, but you are not |
| obligated to do so. If you do not wish to do so, delete this |
| exception statement from your version. */ |
| |
| package java.lang; |
| |
| import java.util.ArrayList; |
| import java.util.Collections; |
| import java.util.Iterator; |
| import java.util.List; |
| import java.util.Map; |
| import java.util.WeakHashMap; |
| |
| /** |
| * A ThreadLocal whose value is inherited by child Threads. The value of the |
| * InheritableThreadLocal associated with the (parent) Thread is copied to |
| * the new (child) Thread at the moment of creation. |
| * |
| * <p>It is possible to make the value associated with the child Thread a |
| * function of the value that is associated with the parent Thread by |
| * overriding the <code>childValue()</code> method. The utility of this class |
| * is in transferring items like User ID or Transaction ID across threads |
| * automatically. |
| * |
| * @author Mark Wielaard (mark@klomp.org) |
| * @author Eric Blake (ebb9@email.byu.edu) |
| * @see ThreadLocal |
| * @since 1.2 |
| * @status updated to 1.4 |
| */ |
| public class InheritableThreadLocal extends ThreadLocal |
| { |
| /** |
| * Maps Threads to a List of InheritableThreadLocals (the heritage of that |
| * Thread). Uses a WeakHashMap so if the Thread is garbage collected the |
| * List can be collected, too. Maps to a list in case the user overrides |
| * equals. |
| */ |
| private static final Map threadMap |
| = Collections.synchronizedMap(new WeakHashMap()); |
| |
| /** |
| * Creates a new InheritableThreadLocal that has no values associated |
| * with it yet. |
| */ |
| public InheritableThreadLocal() |
| { |
| Thread currentThread = Thread.currentThread(); |
| // Note that we don't have to synchronize, as only this thread will |
| // ever modify the returned heritage and threadMap is a synchronizedMap. |
| List heritage = (List) threadMap.get(currentThread); |
| if (heritage == null) |
| { |
| heritage = new ArrayList(); |
| threadMap.put(currentThread, heritage); |
| } |
| heritage.add(this); |
| } |
| |
| /** |
| * Determines the value associated with a newly created child Thread as a |
| * function of the value associated with the currently executing (parent) |
| * Thread. The default implementation just returns the parentValue. |
| * |
| * @param parentValue the value of this object in the parent thread at |
| * the moment of creation of the child |
| * @return the initial value for the child thread |
| */ |
| protected Object childValue(Object parentValue) |
| { |
| return parentValue; |
| } |
| |
| /** |
| * Generates the childValues of all <code>InheritableThreadLocal</code>s |
| * that are in the heritage of the current Thread for the newly created |
| * childThread. Should be called from the contructor Thread. |
| * |
| * @param childThread the newly created thread, to inherit from this thread |
| * @see Thread#Thread(ThreadGroup, Runnable, String) |
| */ |
| static void newChildThread(Thread childThread) |
| { |
| // The currentThread is the parent of the new thread. |
| Thread parentThread = Thread.currentThread(); |
| // Note that we don't have to synchronize, as only this thread will |
| // ever modify the returned heritage and threadMap is a synchronizedMap. |
| ArrayList heritage = (ArrayList) threadMap.get(parentThread); |
| if (heritage != null) |
| { |
| threadMap.put(childThread, heritage.clone()); |
| // Perform the inheritance. |
| Iterator it = heritage.iterator(); |
| int i = heritage.size(); |
| while (--i >= 0) |
| { |
| InheritableThreadLocal local = (InheritableThreadLocal) it.next(); |
| Object parentValue = local.valueMap.get(parentThread); |
| if (parentValue != null) |
| { |
| Object childValue = local.childValue(parentValue == NULL |
| ? null : parentValue); |
| local.valueMap.put(childThread, (childValue == null |
| ? NULL : parentValue)); |
| } |
| } |
| } |
| } |
| } |