1.1 --- a/emul/compact/src/main/java/java/lang/ref/SoftReference.java Fri Mar 22 16:59:47 2013 +0100
1.2 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
1.3 @@ -1,118 +0,0 @@
1.4 -/*
1.5 - * Copyright (c) 1997, 2003, Oracle and/or its affiliates. All rights reserved.
1.6 - * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 - *
1.8 - * This code is free software; you can redistribute it and/or modify it
1.9 - * under the terms of the GNU General Public License version 2 only, as
1.10 - * published by the Free Software Foundation. Oracle designates this
1.11 - * particular file as subject to the "Classpath" exception as provided
1.12 - * by Oracle in the LICENSE file that accompanied this code.
1.13 - *
1.14 - * This code is distributed in the hope that it will be useful, but WITHOUT
1.15 - * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.16 - * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.17 - * version 2 for more details (a copy is included in the LICENSE file that
1.18 - * accompanied this code).
1.19 - *
1.20 - * You should have received a copy of the GNU General Public License version
1.21 - * 2 along with this work; if not, write to the Free Software Foundation,
1.22 - * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.23 - *
1.24 - * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.25 - * or visit www.oracle.com if you need additional information or have any
1.26 - * questions.
1.27 - */
1.28 -
1.29 -package java.lang.ref;
1.30 -
1.31 -
1.32 -/**
1.33 - * Soft reference objects, which are cleared at the discretion of the garbage
1.34 - * collector in response to memory demand. Soft references are most often used
1.35 - * to implement memory-sensitive caches.
1.36 - *
1.37 - * <p> Suppose that the garbage collector determines at a certain point in time
1.38 - * that an object is <a href="package-summary.html#reachability">softly
1.39 - * reachable</a>. At that time it may choose to clear atomically all soft
1.40 - * references to that object and all soft references to any other
1.41 - * softly-reachable objects from which that object is reachable through a chain
1.42 - * of strong references. At the same time or at some later time it will
1.43 - * enqueue those newly-cleared soft references that are registered with
1.44 - * reference queues.
1.45 - *
1.46 - * <p> All soft references to softly-reachable objects are guaranteed to have
1.47 - * been cleared before the virtual machine throws an
1.48 - * <code>OutOfMemoryError</code>. Otherwise no constraints are placed upon the
1.49 - * time at which a soft reference will be cleared or the order in which a set
1.50 - * of such references to different objects will be cleared. Virtual machine
1.51 - * implementations are, however, encouraged to bias against clearing
1.52 - * recently-created or recently-used soft references.
1.53 - *
1.54 - * <p> Direct instances of this class may be used to implement simple caches;
1.55 - * this class or derived subclasses may also be used in larger data structures
1.56 - * to implement more sophisticated caches. As long as the referent of a soft
1.57 - * reference is strongly reachable, that is, is actually in use, the soft
1.58 - * reference will not be cleared. Thus a sophisticated cache can, for example,
1.59 - * prevent its most recently used entries from being discarded by keeping
1.60 - * strong referents to those entries, leaving the remaining entries to be
1.61 - * discarded at the discretion of the garbage collector.
1.62 - *
1.63 - * @author Mark Reinhold
1.64 - * @since 1.2
1.65 - */
1.66 -
1.67 -public class SoftReference<T> extends Reference<T> {
1.68 -
1.69 - /**
1.70 - * Timestamp clock, updated by the garbage collector
1.71 - */
1.72 - static private long clock;
1.73 -
1.74 - /**
1.75 - * Timestamp updated by each invocation of the get method. The VM may use
1.76 - * this field when selecting soft references to be cleared, but it is not
1.77 - * required to do so.
1.78 - */
1.79 - private long timestamp;
1.80 -
1.81 - /**
1.82 - * Creates a new soft reference that refers to the given object. The new
1.83 - * reference is not registered with any queue.
1.84 - *
1.85 - * @param referent object the new soft reference will refer to
1.86 - */
1.87 - public SoftReference(T referent) {
1.88 - super(referent);
1.89 - this.timestamp = clock;
1.90 - }
1.91 -
1.92 - /**
1.93 - * Creates a new soft reference that refers to the given object and is
1.94 - * registered with the given queue.
1.95 - *
1.96 - * @param referent object the new soft reference will refer to
1.97 - * @param q the queue with which the reference is to be registered,
1.98 - * or <tt>null</tt> if registration is not required
1.99 - *
1.100 - */
1.101 - public SoftReference(T referent, ReferenceQueue<? super T> q) {
1.102 - super(referent, q);
1.103 - this.timestamp = clock;
1.104 - }
1.105 -
1.106 - /**
1.107 - * Returns this reference object's referent. If this reference object has
1.108 - * been cleared, either by the program or by the garbage collector, then
1.109 - * this method returns <code>null</code>.
1.110 - *
1.111 - * @return The object to which this reference refers, or
1.112 - * <code>null</code> if this reference object has been cleared
1.113 - */
1.114 - public T get() {
1.115 - T o = super.get();
1.116 - if (o != null && this.timestamp != clock)
1.117 - this.timestamp = clock;
1.118 - return o;
1.119 - }
1.120 -
1.121 -}