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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
committerupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
commit554fd8c5195424bdbcabf5de30fdc183aba391bd (patch)
tree976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/java/lang/ThreadLocal.java
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+/* 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 1.5
+ */
+public class ThreadLocal<T>
+{
+ /**
+ * 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 sentinel = new Object();
+
+ /**
+ * The base for the computation of the next hash for a thread local.
+ */
+ private static int nextHashBase = 1;
+
+ /**
+ * Allocate a new hash.
+ */
+ private synchronized int computeNextHash()
+ {
+ return nextHashBase++ * 6709;
+ }
+
+ /**
+ * Hash code computed for ThreadLocalMap
+ */
+ final int fastHash;
+
+ /**
+ * Creates a ThreadLocal object without associating any value to it yet.
+ */
+ public ThreadLocal()
+ {
+ constructNative();
+ fastHash = computeNextHash();
+ }
+
+ /**
+ * 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 T 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 native T get();
+
+ private final Object internalGet()
+ {
+ ThreadLocalMap map = Thread.getThreadLocals();
+ // Note that we don't have to synchronize, as only this thread will
+ // ever modify the map.
+ T value = (T) map.get(this);
+ if (value == sentinel)
+ {
+ value = initialValue();
+ map.set(this, value);
+ }
+ return 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 native void set(T value);
+
+ private final void internalSet(Object value)
+ {
+ ThreadLocalMap map = Thread.getThreadLocals();
+ // Note that we don't have to synchronize, as only this thread will
+ // ever modify the map.
+ map.set(this, value);
+ }
+
+ /**
+ * Removes the value associated with the ThreadLocal object for the
+ * currently executing Thread.
+ * @since 1.5
+ */
+ public native void remove();
+
+ private final void internalRemove()
+ {
+ ThreadLocalMap map = Thread.getThreadLocals();
+ map.remove(this);
+ }
+
+ protected native void finalize () throws Throwable;
+
+ private native void constructNative();
+
+ private gnu.gcj.RawData TLSPointer;
+}