Initial revision

From-SVN: r102074

libjava/classpath/java/lang/InheritableThreadLocal.java

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+/* 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., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 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.Iterator;
+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
+{
+  /**
+   * Creates a new InheritableThreadLocal that has no values associated
+   * with it yet.
+   */
+  public InheritableThreadLocal()
+  {
+  }
+
+  /**
+   * 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();
+    if (parentThread.locals != null)
+      {
+        Iterator keys = parentThread.locals.keySet().iterator();
+        while (keys.hasNext())
+          {
+            Key key = (Key)keys.next();
+            if (key.get() instanceof InheritableThreadLocal)
+              {
+                InheritableThreadLocal local = (InheritableThreadLocal)key.get();
+                Object parentValue = parentThread.locals.get(key);
+                Object childValue = local.childValue(parentValue == NULL
+                                                     ? null : parentValue);
+                if (childThread.locals == null)
+                    childThread.locals = new WeakHashMap();
+                childThread.locals.put(key, (childValue == null
+                                             ? NULL : childValue));
+              }
+          }
+      }
+  }
+}