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1: /* InheritableThreadLocal -- a ThreadLocal which inherits values across threads 2: Copyright (C) 2000, 2001, 2002, 2003, 2005 Free Software Foundation, Inc. 3: 4: This file is part of GNU Classpath. 5: 6: GNU Classpath is free software; you can redistribute it and/or modify 7: it under the terms of the GNU General Public License as published by 8: the Free Software Foundation; either version 2, or (at your option) 9: any later version. 10: 11: GNU Classpath is distributed in the hope that it will be useful, but 12: WITHOUT ANY WARRANTY; without even the implied warranty of 13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14: General Public License for more details. 15: 16: You should have received a copy of the GNU General Public License 17: along with GNU Classpath; see the file COPYING. If not, write to the 18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19: 02110-1301 USA. 20: 21: Linking this library statically or dynamically with other modules is 22: making a combined work based on this library. Thus, the terms and 23: conditions of the GNU General Public License cover the whole 24: combination. 25: 26: As a special exception, the copyright holders of this library give you 27: permission to link this library with independent modules to produce an 28: executable, regardless of the license terms of these independent 29: modules, and to copy and distribute the resulting executable under 30: terms of your choice, provided that you also meet, for each linked 31: independent module, the terms and conditions of the license of that 32: module. An independent module is a module which is not derived from 33: or based on this library. If you modify this library, you may extend 34: this exception to your version of the library, but you are not 35: obligated to do so. If you do not wish to do so, delete this 36: exception statement from your version. */ 37: 38: package java.lang; 39: 40: import java.util.Iterator; 41: import java.util.WeakHashMap; 42: 43: /** 44: * A ThreadLocal whose value is inherited by child Threads. The value of the 45: * InheritableThreadLocal associated with the (parent) Thread is copied to 46: * the new (child) Thread at the moment of creation. 47: * 48: * <p>It is possible to make the value associated with the child Thread a 49: * function of the value that is associated with the parent Thread by 50: * overriding the <code>childValue()</code> method. The utility of this class 51: * is in transferring items like User ID or Transaction ID across threads 52: * automatically. 53: * 54: * @author Mark Wielaard (mark@klomp.org) 55: * @author Eric Blake (ebb9@email.byu.edu) 56: * @see ThreadLocal 57: * @since 1.2 58: * @status updated to 1.4 59: */ 60: public class InheritableThreadLocal extends ThreadLocal 61: { 62: /** 63: * Creates a new InheritableThreadLocal that has no values associated 64: * with it yet. 65: */ 66: public InheritableThreadLocal() 67: { 68: } 69: 70: /** 71: * Determines the value associated with a newly created child Thread as a 72: * function of the value associated with the currently executing (parent) 73: * Thread. The default implementation just returns the parentValue. 74: * 75: * @param parentValue the value of this object in the parent thread at 76: * the moment of creation of the child 77: * @return the initial value for the child thread 78: */ 79: protected Object childValue(Object parentValue) 80: { 81: return parentValue; 82: } 83: 84: /** 85: * Generates the childValues of all <code>InheritableThreadLocal</code>s 86: * that are in the heritage of the current Thread for the newly created 87: * childThread. Should be called from the contructor Thread. 88: * 89: * @param childThread the newly created thread, to inherit from this thread 90: * @see Thread#Thread(ThreadGroup, Runnable, String) 91: */ 92: static void newChildThread(Thread childThread) 93: { 94: // The currentThread is the parent of the new thread. 95: Thread parentThread = Thread.currentThread(); 96: if (parentThread.locals != null) 97: { 98: Iterator keys = parentThread.locals.keySet().iterator(); 99: while (keys.hasNext()) 100: { 101: Key key = (Key)keys.next(); 102: if (key.get() instanceof InheritableThreadLocal) 103: { 104: InheritableThreadLocal local = (InheritableThreadLocal)key.get(); 105: Object parentValue = parentThread.locals.get(key); 106: Object childValue = local.childValue(parentValue == NULL 107: ? null : parentValue); 108: if (childThread.locals == null) 109: childThread.locals = new WeakHashMap(); 110: childThread.locals.put(key, (childValue == null 111: ? NULL : childValue)); 112: } 113: } 114: } 115: } 116: }
GNU Classpath (0.18) |