1 /*
2  * Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4  *
5  * This code is free software; you can redistribute it and/or modify it
6  * under the terms of the GNU General Public License version 2 only, as
7  * published by the Free Software Foundation.
8  *
9  * This code is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12  * version 2 for more details (a copy is included in the LICENSE file that
13  * accompanied this code).
14  *
15  * You should have received a copy of the GNU General Public License version
16  * 2 along with this work; if not, write to the Free Software Foundation,
17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  *
23  */
24 
25 #ifndef SHARE_GC_SHARED_REFERENCEPOLICY_HPP
26 #define SHARE_GC_SHARED_REFERENCEPOLICY_HPP
27 
28 #include "oops/oopsHierarchy.hpp"
29 
30 // referencePolicy is used to determine when soft reference objects
31 // should be cleared.
32 
33 
34 class ReferencePolicy : public CHeapObj<mtGC> {
35  public:
should_clear_reference(oop p,jlong timestamp_clock)36   virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
37     ShouldNotReachHere();
38     return true;
39   }
40 
41   // Capture state (of-the-VM) information needed to evaluate the policy
setup()42   virtual void setup() { /* do nothing */ }
43 };
44 
45 class NeverClearPolicy : public ReferencePolicy {
46  public:
should_clear_reference(oop p,jlong timestamp_clock)47   virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
48     return false;
49   }
50 };
51 
52 class AlwaysClearPolicy : public ReferencePolicy {
53  public:
should_clear_reference(oop p,jlong timestamp_clock)54   virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
55     return true;
56   }
57 };
58 
59 class LRUCurrentHeapPolicy : public ReferencePolicy {
60  private:
61   jlong _max_interval;
62 
63  public:
64   LRUCurrentHeapPolicy();
65 
66   // Capture state (of-the-VM) information needed to evaluate the policy
67   void setup();
68   virtual bool should_clear_reference(oop p, jlong timestamp_clock);
69 };
70 
71 class LRUMaxHeapPolicy : public ReferencePolicy {
72  private:
73   jlong _max_interval;
74 
75  public:
76   LRUMaxHeapPolicy();
77 
78   // Capture state (of-the-VM) information needed to evaluate the policy
79   void setup();
80   virtual bool should_clear_reference(oop p, jlong timestamp_clock);
81 };
82 
83 #endif // SHARE_GC_SHARED_REFERENCEPOLICY_HPP
84