| /* ThreadLocal -- a variable with a unique value per thread |
| Copyright (C) 2000, 2002, 2003, 2006 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.Map; |
| |
| |
| /** |
| * ThreadLocal objects have a different state associated with every |
| * Thread that accesses them. Every access to the ThreadLocal object |
| * (through the <code>get()</code> and <code>set()</code> methods) |
| * only affects the state of the object as seen by the currently |
| * executing Thread. |
| * |
| * <p>The first time a ThreadLocal object is accessed on a particular |
| * Thread, the state for that Thread's copy of the local variable is set by |
| * executing the method <code>initialValue()</code>. |
| * </p> |
| * |
| * <p>An example how you can use this: |
| * </p> |
| * |
| * <pre> |
| * class Connection |
| * { |
| * private static ThreadLocal owner = new ThreadLocal() |
| * { |
| * public Object initialValue() |
| * { |
| * return("nobody"); |
| * } |
| * }; |
| * ... |
| * } |
| * </pre> |
| * |
| * <p>Now all instances of connection can see who the owner of the currently |
| * executing Thread is by calling <code>owner.get()</code>. By default any |
| * Thread would be associated with 'nobody'. But the Connection object could |
| * offer a method that changes the owner associated with the Thread on |
| * which the method was called by calling <code>owner.put("somebody")</code>. |
| * (Such an owner changing method should then be guarded by security checks.) |
| * </p> |
| * |
| * <p>When a Thread is garbage collected all references to values of |
| * the ThreadLocal objects associated with that Thread are removed. |
| * </p> |
| * |
| * @author Mark Wielaard (mark@klomp.org) |
| * @author Eric Blake (ebb9@email.byu.edu) |
| * @since 1.2 |
| * @status updated to 1.4 |
| */ |
| public class ThreadLocal |
| { |
| /** |
| * Placeholder to distinguish between uninitialized and null set by the |
| * user. Do not expose this to the public. Package visible for use by |
| * InheritableThreadLocal |
| */ |
| static final Object NULL = new Object(); |
| |
| /** |
| * Creates a ThreadLocal object without associating any value to it yet. |
| */ |
| public ThreadLocal() |
| { |
| } |
| |
| /** |
| * Called once per thread on the first invocation of get(), if set() was |
| * not already called. The default implementation returns <code>null</code>. |
| * Often, this method is overridden to create the appropriate initial object |
| * for the current thread's view of the ThreadLocal. |
| * |
| * @return the initial value of the variable in this thread |
| */ |
| protected Object initialValue() |
| { |
| return null; |
| } |
| |
| /** |
| * Gets the value associated with the ThreadLocal object for the currently |
| * executing Thread. If this is the first time the current thread has called |
| * get(), and it has not already called set(), the value is obtained by |
| * <code>initialValue()</code>. |
| * |
| * @return the value of the variable in this thread |
| */ |
| public Object get() |
| { |
| Map map = Thread.getThreadLocals(); |
| // Note that we don't have to synchronize, as only this thread will |
| // ever modify the map. |
| Object value = map.get(this); |
| if (value == null) |
| { |
| value = initialValue(); |
| map.put(this, value == null ? NULL : value); |
| } |
| return value == NULL ? null : value; |
| } |
| |
| /** |
| * Sets the value associated with the ThreadLocal object for the currently |
| * executing Thread. This overrides any existing value associated with the |
| * current Thread and prevents <code>initialValue()</code> from being |
| * called if this is the first access to this ThreadLocal in this Thread. |
| * |
| * @param value the value to set this thread's view of the variable to |
| */ |
| public void set(Object value) |
| { |
| Map map = Thread.getThreadLocals(); |
| // Note that we don't have to synchronize, as only this thread will |
| // ever modify the map. |
| map.put(this, value == null ? NULL : value); |
| } |
| |
| /** |
| * Removes the value associated with the ThreadLocal object for the |
| * currently executing Thread. |
| * @since 1.5 |
| */ |
| public void remove() |
| { |
| Map map = Thread.getThreadLocals(); |
| map.remove(this); |
| } |
| } |