--- /dev/null
+/* java.lang.InheritableThreadLocal
+ Copyright (C) 2000, 2001 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.
+
+As a special exception, if you link this library with other files to
+produce an executable, this library does not by itself cause the
+resulting executable to be covered by the GNU General Public License.
+This exception does not however invalidate any other reasons why the
+executable file might be covered by the GNU General Public License. */
+
+package java.lang;
+
+import java.util.Iterator;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.WeakHashMap;
+
+/**
+ * ThreadLocal whose value is inherited by child Threads.
+ * The value of the InheritableThreadLocal associated with the (parent) Thread
+ * on the moment that it creates a new (child) Thread is set as the value that
+ * is associated with the new (child) Thread.
+ * <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.
+ *
+ * @since 1.2
+ * @author Mark Wielaard (mark@klomp.org)
+ */
+public class InheritableThreadLocal extends ThreadLocal {
+
+ /**
+ * Maps Threads to a Set of InheritableThreadLocals
+ * (the heritage of that Thread).
+ * Uses a WeakHashMap so if the Thread is garbage collected the reference
+ * to that Set disappears.
+ * Both <code>AddToHeritage</code> access and modify it so they have to
+ * synchronize on the threadMap when they do.
+ */
+ private static Map threadMap = new WeakHashMap();
+
+ /**
+ * Creates a new InheritableThreadLocal that has no values associated
+ * with it yet.
+ */
+ public InheritableThreadLocal() {
+ super();
+ }
+
+ /**
+ * Determines the value associated with a newly created child Thread
+ * as a function of the value associated with the currently executing
+ * (parent) Thread.
+ * <p>
+ * The default implementation just returns the parentValue.
+ */
+ protected Object childValue(Object parentValue) {
+ return parentValue;
+ }
+
+ /**
+ * Adds this <code>InheritableThreadLocal</code> to the heritage of the
+ * current Thread and returns the value of the <code>ThreadLocal</code>
+ * for the Thread. The value will be either the last value that the
+ * current Thread has set, or the childValue of the last value that the
+ * parent Thread set before the current Thread was created, or the
+ * initialValue of the <code>ThreadLocal</code>.
+ *
+ * @see ThreadLocal#get()
+ */
+ public Object get() {
+ addToHeritage();
+ return super.get();
+ }
+
+ /**
+ * Adds this <code>InheritableThreadLocal</code> to the heritage of the
+ * current Thread and sets the value of the <code>ThreadLocal</code>
+ * for the Thread.
+ *
+ * @see ThreadLocal#set(Object)
+ */
+ public void set(Object value) {
+ addToHeritage();
+ super.set(value);
+ }
+
+ /**
+ * Adds this <code>InheritableThreadLocal</code> to the heritage
+ * of the current Thread.
+ */
+ private void addToHeritage() {
+ Thread currentThread = Thread.currentThread();
+ Set heritage;
+ synchronized(threadMap) {
+ heritage = (Set)threadMap.get(currentThread);
+ }
+ // Note that we don't have to synchronize on the heritage Set
+ // since only this Thread (or the parent Thread when creating
+ // the heritage) ever modifies it.
+ if (heritage == null) {
+ heritage = new HashSet();
+ synchronized(threadMap) {
+ threadMap.put(currentThread, heritage);
+ }
+ }
+ if (!heritage.contains(this)) {
+ heritage.add(this);
+ }
+ }
+
+ /**
+ * 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 of java.lang.Thread.
+ */
+ static void newChildThread(Thread childThread) {
+ // The currentThread is the parent of the new thread
+ Thread parentThread = Thread.currentThread();
+
+ // Inherit all the InheritableThreadLocals of the parent thread
+ Set heritage;
+ synchronized(threadMap) {
+ heritage = (Set)threadMap.get(parentThread);
+ }
+ // Note that we don't have to synchronize on the heritage Set
+ // since only this Thread (or the parent Thread when creating
+ // the heritage) ever modifies it.
+ if (heritage != null) {
+ synchronized(threadMap) {
+ threadMap.put(childThread, new HashSet(heritage));
+ }
+ // And constructs all the new child values
+ // (has to be done now that we are executing in the parentThread)
+ Iterator it = heritage.iterator();
+ while (it.hasNext()) {
+ InheritableThreadLocal local =
+ (InheritableThreadLocal) it.next();
+ // Note that the parentValue cannot be null
+ // If it was it would not be in the heritage
+ Object parentValue = local.get(parentThread).getValue();
+ Object childValue = local.childValue(parentValue);
+ ThreadLocal.Value v = new ThreadLocal.Value(childValue);
+ local.set(childThread, v);
+ }
+ }
+ }
+}
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