Initial revision

From-SVN: r102074

6 files changed, 604 insertions, 0 deletions

diff --git a/libjava/classpath/java/lang/ref/PhantomReference.java b/libjava/classpath/java/lang/ref/PhantomReference.java
new file mode 100644
index 0000000..4d929c2
--- /dev/null
+++ b/libjava/classpath/java/lang/ref/PhantomReference.java
@@ -0,0 +1,73 @@
+/* java.lang.ref.PhantomReference
+   Copyright (C) 1999 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;
+
+/**
+ * A phantom reference is useful, to get notified, when an object got
+ * finalized.  You can't access that object though, since it is
+ * finalized.  This is the reason, why <code>get()</code> always
+ * returns null.
+ *
+ * @author Jochen Hoenicke 
+ */
+public class PhantomReference 
+  extends Reference
+{
+  /**
+   * Creates a new phantom reference.
+   * @param referent the object that should be watched.
+   * @param q the queue that should be notified, if the referent was
+   * finalized.  This mustn't be <code>null</code>.
+   * @exception NullPointerException if q is null.
+   */
+  public PhantomReference(Object referent, ReferenceQueue q)
+  {
+    super(referent, q);
+  }
+  
+  /**
+   * Returns the object, this reference refers to.
+   * @return <code>null</code>, since the refered object may be
+   * finalized and thus not accessible.  
+   */
+  public Object get()
+  {
+    return null;
+  }
+}
diff --git a/libjava/classpath/java/lang/ref/Reference.java b/libjava/classpath/java/lang/ref/Reference.java
new file mode 100644
index 0000000..1ec7243
--- /dev/null
+++ b/libjava/classpath/java/lang/ref/Reference.java
@@ -0,0 +1,177 @@
+/* java.lang.ref.Reference
+   Copyright (C) 1999, 2002, 2003 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
+{
+  /**
+   * The underlying object.  This field is handled in a special way by
+   * the garbage collector.
+   */
+  Object referent;
+
+  /**
+   * The queue this reference is registered on. This is null, if this
+   * wasn't registered to any queue or reference was already enqueued.
+   */
+  ReferenceQueue 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(Object ref)
+  {
+    referent = 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(Object ref, ReferenceQueue q)
+  {
+    if (q == null)
+      throw new NullPointerException();
+    referent = ref;
+    queue = q;
+  }
+
+  /**
+   * Returns the object, this reference refers to.
+   * @return the object, this reference refers to, or null if the 
+   * reference was cleared.
+   */
+  public Object get()
+  {
+    synchronized (lock)
+      {
+	return referent;
+      }
+  }
+
+  /**
+   * 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()
+  {
+    referent = null;
+  }
+
+  /**
+   * 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;
+  }
+}
diff --git a/libjava/classpath/java/lang/ref/ReferenceQueue.java b/libjava/classpath/java/lang/ref/ReferenceQueue.java
new file mode 100644
index 0000000..f4729f2
--- /dev/null
+++ b/libjava/classpath/java/lang/ref/ReferenceQueue.java
@@ -0,0 +1,145 @@
+/* java.lang.ref.ReferenceQueue
+   Copyright (C) 1999 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 queue, where references can enqueue themselve on.  Each
+ * reference may be registered to a queue at initialization time and
+ * will be appended to the queue, when the enqueue method is called.
+ *
+ * The enqueue method may be automatically called by the garbage
+ * collector if it detects, that the object is only reachable through
+ * the Reference objects.
+ *
+ * @author Jochen Hoenicke
+ * @see Reference#enqueue()
+ */
+public class ReferenceQueue
+{
+  /**
+   * This is a linked list of references.  If this is null, the list is
+   * empty.  Otherwise this points to the first reference on the queue.
+   * The first reference will point to the next reference via the 
+   * <code>nextOnQueue</code> field.  The last reference will point to
+   * itself (not to null, since <code>nextOnQueue</code> is used to 
+   * determine if a reference is enqueued).
+   */
+  private Reference first;
+
+  /**
+   * Creates a new empty reference queue.
+   */
+  public ReferenceQueue()
+  {
+  }
+
+  /**
+   * Checks if there is a reference on the queue, returning it
+   * immediately.  The reference will be dequeued.
+   *
+   * @return a reference on the queue, if there is one,
+   * <code>null</code> otherwise.  
+   */
+  public synchronized Reference poll()
+  { 
+    return dequeue();
+  }
+
+  /**
+   * This is called by reference to enqueue itself on this queue.  
+   * @param ref the reference that should be enqueued.
+   */
+  synchronized void enqueue(Reference ref)
+  {
+    /* last reference will point to itself */
+    ref.nextOnQueue = first == null ? ref : first;
+    first = ref;
+    /* this wakes only one remove thread. */
+    notify();
+  }
+
+  /**
+   * Remove a reference from the queue, if there is one.
+   * @return the first element of the queue, or null if there isn't any.
+   */
+  private Reference dequeue()
+  {
+    if (first == null)
+      return null;
+
+    Reference result = first;
+    first = (first == first.nextOnQueue) ? null : first.nextOnQueue;
+    result.nextOnQueue = null;
+    return result;
+  }
+
+  /**
+   * Removes a reference from the queue, blocking for <code>timeout</code>
+   * until a reference is enqueued.
+   * @param timeout the timeout period in milliseconds, <code>0</code> means
+   * wait forever.
+   * @return the reference removed from the queue, or 
+   * <code>null</code> if timeout period expired.  
+   * @exception InterruptedException if the wait was interrupted.
+   */
+  public synchronized Reference remove(long timeout)
+    throws InterruptedException
+  {
+    if (first == null)
+      {
+	wait(timeout);
+      }
+
+    return dequeue();
+  }
+    
+
+  /**
+   * Removes a reference from the queue, blocking until a reference is
+   * enqueued.
+   *
+   * @return the reference removed from the queue.  
+   * @exception InterruptedException if the wait was interrupted.
+   */
+  public Reference remove()
+    throws InterruptedException
+  {
+    return remove(0L);
+  }
+}
diff --git a/libjava/classpath/java/lang/ref/SoftReference.java b/libjava/classpath/java/lang/ref/SoftReference.java
new file mode 100644
index 0000000..97395ea
--- /dev/null
+++ b/libjava/classpath/java/lang/ref/SoftReference.java
@@ -0,0 +1,84 @@
+/* java.lang.ref.SoftReference
+   Copyright (C) 1999 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;
+
+/**
+ * A soft reference will be cleared, if the object is only softly
+ * reachable and the garbage collection needs more memory.  The garbage
+ * collection will use an intelligent strategy to determine which soft
+ * references it should clear.  This makes a soft reference ideal for
+ * caches.<br>
+ *
+ * @author Jochen Hoenicke 
+ */
+public class SoftReference 
+  extends Reference
+{
+  /**
+   * Create a new soft reference, that is not registered to any queue.
+   * @param referent the object we refer to.
+   */
+  public SoftReference(Object referent)
+  {
+    super(referent);
+  }
+
+  /**
+   * Create a new soft reference.
+   * @param referent the object we refer to.
+   * @param q the reference queue to register on.
+   * @exception NullPointerException if q is null.
+   */
+  public SoftReference(Object referent, ReferenceQueue q)
+  {
+    super(referent, q);
+  }
+  
+  /**
+   * Returns the object, this reference refers to.
+   * @return the object, this reference refers to, or null if the 
+   * reference was cleared.
+   */
+  public Object get()
+  {
+    /* Why is this overloaded??? 
+     * Maybe for a kind of LRU strategy. */
+    return super.get();
+  }
+}
diff --git a/libjava/classpath/java/lang/ref/WeakReference.java b/libjava/classpath/java/lang/ref/WeakReference.java
new file mode 100644
index 0000000..9f758ca
--- /dev/null
+++ b/libjava/classpath/java/lang/ref/WeakReference.java
@@ -0,0 +1,79 @@
+/* java.lang.ref.WeakReference
+   Copyright (C) 1999 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;
+
+/**
+ * A weak reference will be cleared, if the object is only weakly
+ * reachable.  It is useful for lookup tables, where you aren't
+ * interested in an entry, if the key isn't reachable anymore.
+ * <code>WeakHashtable</code> is a complete implementation of such a
+ * table. <br>
+ *
+ * It is also useful to make objects unique: You create a set of weak
+ * references to those objects, and when you create a new object you
+ * look in this set, if the object already exists and return it.  If
+ * an object is not referenced anymore, the reference will
+ * automatically cleared, and you may remove it from the set. <br>
+ *
+ * @author Jochen Hoenicke 
+ * @see java.util.WeakHashtable 
+ */
+public class WeakReference 
+  extends Reference
+{
+  /**
+   * Create a new weak reference, that is not registered to any queue.
+   * @param referent the object we refer to.
+   */
+  public WeakReference(Object referent)
+  {
+    super(referent);
+  }
+
+  /**
+   * Create a new weak reference.
+   * @param referent the object we refer to.
+   * @param q the reference queue to register on.
+   * @exception NullPointerException if q is null.
+   */
+  public WeakReference(Object referent, ReferenceQueue q)
+  {
+    super(referent, q);
+  }
+}
diff --git a/libjava/classpath/java/lang/ref/package.html b/libjava/classpath/java/lang/ref/package.html
new file mode 100644
index 0000000..d3d1762
--- /dev/null
+++ b/libjava/classpath/java/lang/ref/package.html
@@ -0,0 +1,46 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
+<!-- package.html - describes classes in java.lang.ref package.
+   Copyright (C) 2002 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. -->
+
+<html>
+<head><title>GNU Classpath - java.lang.ref</title></head>
+
+<body>
+<p>Low level manipulation and monitoring of object references.</p>
+
+</body>
+</html>