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Diffstat (limited to 'libjava/java/lang/ref/Reference.java')
| -rw-r--r-- | libjava/java/lang/ref/Reference.java | 204 |
1 files changed, 0 insertions, 204 deletions
diff --git a/libjava/java/lang/ref/Reference.java b/libjava/java/lang/ref/Reference.java deleted file mode 100644 index a5184cee888..00000000000 --- a/libjava/java/lang/ref/Reference.java +++ /dev/null @@ -1,204 +0,0 @@ -/* java.lang.ref.Reference - Copyright (C) 1999, 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.ref; - -/** - * This is the base class of all references. A reference allows - * refering to an object without preventing the garbage collector to - * collect it. The only way to get the referred object is via the - * <code>get()</code>-method. This method will return - * <code>null</code> if the object was collected. <br> - * - * A reference may be registered with a queue. When a referred - * element gets collected the reference will be put on the queue, so - * that you will be notified. <br> - * - * There are currently three types of references: soft reference, - * weak reference and phantom reference. <br> - * - * Soft references will be cleared if the garbage collector is told - * to free some memory and there are no unreferenced or weakly referenced - * objects. It is useful for caches. <br> - * - * Weak references will be cleared as soon as the garbage collector - * determines that the refered object is only weakly reachable. They - * are useful as keys in hashtables (see <code>WeakHashtable</code>) as - * you get notified when nobody has the key anymore. - * - * Phantom references don't prevent finalization. If an object is only - * phantom reachable, it will be finalized, and the reference will be - * enqueued, but not cleared. Since you mustn't access an finalized - * object, the <code>get</code> method of a phantom reference will never - * work. It is useful to keep track, when an object is finalized. - * - * @author Jochen Hoenicke - * @see java.util.WeakHashtable - */ -public abstract class Reference<T> -{ - /** - * The underlying object. This field is handled in a special way by - * the garbage collector. - * GCJ LOCAL: - * This is a RawData because it must be disguised from the GC. - * END GCJ LOCAL - */ - gnu.gcj.RawData referent; - - /** - * This is like REFERENT but is not scanned by the GC. We keep a - * copy around so that we can clean up our internal data structure - * even after clear() is called. - * GCJ LOCAL: - * This field doesn't exist in Classpath. - * END GCJ LOCAL - */ - gnu.gcj.RawData copy; - - /** - * Set to true if {@link #clear()} is called. - * GCJ LOCAL: - * This field doesn't exist in Classpath. It is used internally in - * natReference.cc, which enqueues the reference unless it is true - * (has been cleared). - * END GCJ LOCAL - */ - boolean cleared = false; - - /** - * The queue this reference is registered on. This is null, if this - * wasn't registered to any queue or reference was already enqueued. - */ - ReferenceQueue<? super T> queue; - - /** - * Link to the next entry on the queue. If this is null, this - * reference is not enqueued. Otherwise it points to the next - * reference. The last reference on a queue will point to itself - * (not to null, that value is used to mark a not enqueued - * reference). - */ - Reference nextOnQueue; - - /** - * This lock should be taken by the garbage collector, before - * determining reachability. It will prevent the get()-method to - * return the reference so that reachability doesn't change. - */ - static Object lock = new Object(); - - /** - * Creates a new reference that is not registered to any queue. - * Since it is package private, it is not possible to overload this - * class in a different package. - * @param referent the object we refer to. - */ - Reference(T ref) - { - create (ref); - } - - /** - * Creates a reference that is registered to a queue. Since this is - * package private, it is not possible to overload this class in a - * different package. - * @param referent the object we refer to. - * @param q the reference queue to register on. - * @exception NullPointerException if q is null. - */ - Reference(T ref, ReferenceQueue<? super T> q) - { - if (q == null) - throw new NullPointerException(); - queue = q; - create (ref); - } - - /** - * Notifies the VM that a new Reference has been created. - */ - private native void create (T o); - - /** - * Returns the object, this reference refers to. - * @return the object, this reference refers to, or null if the - * reference was cleared. - */ - public native T get(); - - /** - * Clears the reference, so that it doesn't refer to its object - * anymore. For soft and weak references this is called by the - * garbage collector. For phantom references you should call - * this when enqueuing the reference. - */ - public void clear() - { - // Must synchronize so changes are visible in finalizer thread. - synchronized (lock) - { - referent = null; - cleared = true; - } - } - - /** - * Tells if the object is enqueued on a reference queue. - * @return true if it is enqueued, false otherwise. - */ - public boolean isEnqueued() - { - return nextOnQueue != null; - } - - /** - * Enqueue an object on a reference queue. This is normally executed - * by the garbage collector. - */ - public boolean enqueue() - { - if (queue != null && nextOnQueue == null) - { - queue.enqueue(this); - queue = null; - return true; - } - return false; - } -} |