8187443: Forest Consolidation: Move files to unified layout

Reviewed-by: darcy, ihse

src/java.base/share/classes/java/lang/ref/package-info.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 1998, 2016, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code 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
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * Provides reference-object classes, which support a limited degree
+ * of interaction with the garbage collector.  A program may use a
+ * reference object to maintain a reference to some other object in
+ * such a way that the latter object may still be reclaimed by the
+ * collector.  A program may also arrange to be notified some time
+ * after the collector has determined that the reachability of a given
+ * object has changed.
+ *
+ *<h2>Package Specification</h2>
+ *
+ * A <em>reference object</em> encapsulates a reference to some other
+ * object so that the reference itself may be examined and manipulated
+ * like any other object.  Three types of reference objects are
+ * provided, each weaker than the last: <em>soft</em>, <em>weak</em>,
+ * and <em>phantom</em>.  Each type corresponds to a different level
+ * of reachability, as defined below.  Soft references are for
+ * implementing memory-sensitive caches, weak references are for
+ * implementing canonicalizing mappings that do not prevent their keys
+ * (or values) from being reclaimed, and phantom references are for
+ * scheduling post-mortem cleanup actions.
+ * Post-mortem cleanup actions can be registered and managed by a
+ * {@link java.lang.ref.Cleaner}.
+ *
+ * <p> Each reference-object type is implemented by a subclass of the
+ * abstract base {@link java.lang.ref.Reference} class.
+ * An instance of one of these subclasses encapsulates a single
+ * reference to a particular object, called the <em>referent</em>.
+ * Every reference object provides methods for getting and clearing
+ * the reference.  Aside from the clearing operation reference objects
+ * are otherwise immutable, so no {@code set} operation is
+ * provided.  A program may further subclass these subclasses, adding
+ * whatever fields and methods are required for its purposes, or it
+ * may use these subclasses without change.
+ *
+ * <h3>Notification</h3>
+ *
+ * A program may request to be notified of changes in an object's
+ * reachability by <em>registering</em> an appropriate reference
+ * object with a <em>reference queue</em> at the time the reference
+ * object is created.  Some time after the garbage collector
+ * determines that the reachability of the referent has changed to the
+ * value corresponding to the type of the reference, it will clear the
+ * reference and add it to the associated queue.  At this point, the
+ * reference is considered to be <em>enqueued</em>.  The program may remove
+ * references from a queue either by polling or by blocking until a
+ * reference becomes available.  Reference queues are implemented by
+ * the {@link java.lang.ref.ReferenceQueue} class.
+ *
+ * <p> The relationship between a registered reference object and its
+ * queue is one-sided.  That is, a queue does not keep track of the
+ * references that are registered with it.  If a registered reference
+ * becomes unreachable itself, then it will never be enqueued.  It is
+ * the responsibility of the program using reference objects to ensure
+ * that the objects remain reachable for as long as the program is
+ * interested in their referents.
+ *
+ * <p> While some programs will choose to dedicate a thread to
+ * removing reference objects from one or more queues and processing
+ * them, this is by no means necessary.  A tactic that often works
+ * well is to examine a reference queue in the course of performing
+ * some other fairly-frequent action.  For example, a hashtable that
+ * uses weak references to implement weak keys could poll its
+ * reference queue each time the table is accessed.  This is how the
+ * {@link java.util.WeakHashMap} class works.  Because
+ * the {@link java.lang.ref.ReferenceQueue#poll
+ * ReferenceQueue.poll} method simply checks an internal data
+ * structure, this check will add little overhead to the hashtable
+ * access methods.
+ *
+ * <a id="reachability"></a>
+ * <h3>Reachability</h3>
+ *
+ * Going from strongest to weakest, the different levels of
+ * reachability reflect the life cycle of an object.  They are
+ * operationally defined as follows:
+ *
+ * <ul>
+ *
+ * <li> An object is <em>strongly reachable</em> if it can be reached
+ * by some thread without traversing any reference objects.  A
+ * newly-created object is strongly reachable by the thread that
+ * created it.
+ *
+ * <li> An object is <em>softly reachable</em> if it is not strongly
+ * reachable but can be reached by traversing a soft reference.
+ *
+ * <li> An object is <em>weakly reachable</em> if it is neither
+ * strongly nor softly reachable but can be reached by traversing a
+ * weak reference.  When the weak references to a weakly-reachable
+ * object are cleared, the object becomes eligible for finalization.
+ *
+ * <li> An object is <em>phantom reachable</em> if it is neither
+ * strongly, softly, nor weakly reachable, it has been finalized, and
+ * some phantom reference refers to it.
+ *
+ * <li> Finally, an object is <em>unreachable</em>, and therefore
+ * eligible for reclamation, when it is not reachable in any of the
+ * above ways.
+ *
+ * </ul>
+ *
+ * @author        Mark Reinhold
+ * @since         1.2
+ */
+package java.lang.ref;