src/java.rmi/share/classes/sun/rmi/server/WeakClassHashMap.java
author rehn
Fri, 29 Nov 2019 12:09:25 +0100
changeset 59325 3636bab5e81e
parent 47216 71c04702a3d5
permissions -rw-r--r--
8234086: VM operation can be simplified Reviewed-by: kbarrett, dholmes, dcubed
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
2
90ce3da70b43 Initial load
duke
parents:
diff changeset
     1
/*
14342
8435a30053c1 7197491: update copyright year to match last edit in jdk8 jdk repository
alanb
parents: 12040
diff changeset
     2
 * Copyright (c) 2003, 2012, Oracle and/or its affiliates. All rights reserved.
2
90ce3da70b43 Initial load
duke
parents:
diff changeset
     3
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
90ce3da70b43 Initial load
duke
parents:
diff changeset
     4
 *
90ce3da70b43 Initial load
duke
parents:
diff changeset
     5
 * This code is free software; you can redistribute it and/or modify it
90ce3da70b43 Initial load
duke
parents:
diff changeset
     6
 * under the terms of the GNU General Public License version 2 only, as
5506
202f599c92aa 6943119: Rebrand source copyright notices
ohair
parents: 715
diff changeset
     7
 * published by the Free Software Foundation.  Oracle designates this
2
90ce3da70b43 Initial load
duke
parents:
diff changeset
     8
 * particular file as subject to the "Classpath" exception as provided
5506
202f599c92aa 6943119: Rebrand source copyright notices
ohair
parents: 715
diff changeset
     9
 * by Oracle in the LICENSE file that accompanied this code.
2
90ce3da70b43 Initial load
duke
parents:
diff changeset
    10
 *
90ce3da70b43 Initial load
duke
parents:
diff changeset
    11
 * This code is distributed in the hope that it will be useful, but WITHOUT
90ce3da70b43 Initial load
duke
parents:
diff changeset
    12
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
90ce3da70b43 Initial load
duke
parents:
diff changeset
    13
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
90ce3da70b43 Initial load
duke
parents:
diff changeset
    14
 * version 2 for more details (a copy is included in the LICENSE file that
90ce3da70b43 Initial load
duke
parents:
diff changeset
    15
 * accompanied this code).
90ce3da70b43 Initial load
duke
parents:
diff changeset
    16
 *
90ce3da70b43 Initial load
duke
parents:
diff changeset
    17
 * You should have received a copy of the GNU General Public License version
90ce3da70b43 Initial load
duke
parents:
diff changeset
    18
 * 2 along with this work; if not, write to the Free Software Foundation,
90ce3da70b43 Initial load
duke
parents:
diff changeset
    19
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
90ce3da70b43 Initial load
duke
parents:
diff changeset
    20
 *
5506
202f599c92aa 6943119: Rebrand source copyright notices
ohair
parents: 715
diff changeset
    21
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
202f599c92aa 6943119: Rebrand source copyright notices
ohair
parents: 715
diff changeset
    22
 * or visit www.oracle.com if you need additional information or have any
202f599c92aa 6943119: Rebrand source copyright notices
ohair
parents: 715
diff changeset
    23
 * questions.
2
90ce3da70b43 Initial load
duke
parents:
diff changeset
    24
 */
90ce3da70b43 Initial load
duke
parents:
diff changeset
    25
package sun.rmi.server;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    26
90ce3da70b43 Initial load
duke
parents:
diff changeset
    27
import java.lang.ref.Reference;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    28
import java.lang.ref.SoftReference;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    29
import java.util.Map;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    30
import java.util.WeakHashMap;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    31
90ce3da70b43 Initial load
duke
parents:
diff changeset
    32
/**
90ce3da70b43 Initial load
duke
parents:
diff changeset
    33
 * Abstract class that maps Class objects to lazily-computed values of
90ce3da70b43 Initial load
duke
parents:
diff changeset
    34
 * type V.  A concrete subclass must implement the computeValue method
90ce3da70b43 Initial load
duke
parents:
diff changeset
    35
 * to determine how the values are computed.
90ce3da70b43 Initial load
duke
parents:
diff changeset
    36
 *
90ce3da70b43 Initial load
duke
parents:
diff changeset
    37
 * The keys are only weakly reachable through this map, so this map
90ce3da70b43 Initial load
duke
parents:
diff changeset
    38
 * does not prevent a class (along with its class loader, etc.) from
90ce3da70b43 Initial load
duke
parents:
diff changeset
    39
 * being garbage collected if it is not otherwise strongly reachable.
90ce3da70b43 Initial load
duke
parents:
diff changeset
    40
 * The values are only softly reachable through this map, so that the
90ce3da70b43 Initial load
duke
parents:
diff changeset
    41
 * computed values generally persist while not otherwise strongly
90ce3da70b43 Initial load
duke
parents:
diff changeset
    42
 * reachable, but their storage may be reclaimed if necessary.  Also,
90ce3da70b43 Initial load
duke
parents:
diff changeset
    43
 * note that if a key is strongly reachable from a value, then the key
90ce3da70b43 Initial load
duke
parents:
diff changeset
    44
 * is effectively softly reachable through this map, which may delay
90ce3da70b43 Initial load
duke
parents:
diff changeset
    45
 * garbage collection of classes (see 4429536).
90ce3da70b43 Initial load
duke
parents:
diff changeset
    46
 **/
90ce3da70b43 Initial load
duke
parents:
diff changeset
    47
public abstract class WeakClassHashMap<V> {
90ce3da70b43 Initial load
duke
parents:
diff changeset
    48
12040
558b0e0d5910 7146763: Warnings cleanup in the sun.rmi and related packages
khazra
parents: 5506
diff changeset
    49
    private Map<Class<?>,ValueCell<V>> internalMap = new WeakHashMap<>();
2
90ce3da70b43 Initial load
duke
parents:
diff changeset
    50
90ce3da70b43 Initial load
duke
parents:
diff changeset
    51
    protected WeakClassHashMap() { }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    52
90ce3da70b43 Initial load
duke
parents:
diff changeset
    53
    public V get(Class<?> remoteClass) {
90ce3da70b43 Initial load
duke
parents:
diff changeset
    54
        /*
90ce3da70b43 Initial load
duke
parents:
diff changeset
    55
         * Use a mutable cell (a one-element list) to hold the soft
90ce3da70b43 Initial load
duke
parents:
diff changeset
    56
         * reference to a value, to allow the lazy value computation
90ce3da70b43 Initial load
duke
parents:
diff changeset
    57
         * to be synchronized with entry-level granularity instead of
90ce3da70b43 Initial load
duke
parents:
diff changeset
    58
         * by locking the whole table.
90ce3da70b43 Initial load
duke
parents:
diff changeset
    59
         */
90ce3da70b43 Initial load
duke
parents:
diff changeset
    60
        ValueCell<V> valueCell;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    61
        synchronized (internalMap) {
90ce3da70b43 Initial load
duke
parents:
diff changeset
    62
            valueCell = internalMap.get(remoteClass);
90ce3da70b43 Initial load
duke
parents:
diff changeset
    63
            if (valueCell == null) {
90ce3da70b43 Initial load
duke
parents:
diff changeset
    64
                valueCell = new ValueCell<V>();
90ce3da70b43 Initial load
duke
parents:
diff changeset
    65
                internalMap.put(remoteClass, valueCell);
90ce3da70b43 Initial load
duke
parents:
diff changeset
    66
            }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    67
        }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    68
        synchronized (valueCell) {
90ce3da70b43 Initial load
duke
parents:
diff changeset
    69
            V value = null;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    70
            if (valueCell.ref != null) {
51
6fe31bc95bbc 6600143: Remove another 450 unnecessary casts
martin
parents: 2
diff changeset
    71
                value = valueCell.ref.get();
2
90ce3da70b43 Initial load
duke
parents:
diff changeset
    72
            }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    73
            if (value == null) {
90ce3da70b43 Initial load
duke
parents:
diff changeset
    74
                value = computeValue(remoteClass);
90ce3da70b43 Initial load
duke
parents:
diff changeset
    75
                valueCell.ref = new SoftReference<V>(value);
90ce3da70b43 Initial load
duke
parents:
diff changeset
    76
            }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    77
            return value;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    78
        }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    79
    }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    80
90ce3da70b43 Initial load
duke
parents:
diff changeset
    81
    protected abstract V computeValue(Class<?> remoteClass);
90ce3da70b43 Initial load
duke
parents:
diff changeset
    82
90ce3da70b43 Initial load
duke
parents:
diff changeset
    83
    private static class ValueCell<T> {
90ce3da70b43 Initial load
duke
parents:
diff changeset
    84
        Reference<T> ref = null;
90ce3da70b43 Initial load
duke
parents:
diff changeset
    85
        ValueCell() { }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    86
    }
90ce3da70b43 Initial load
duke
parents:
diff changeset
    87
}