1 /*
   2  * Copyright (c) 2000, 2012, 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
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  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
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  24 
  25 #ifndef SHARE_VM_MEMORY_REFERENCEPOLICY_HPP
  26 #define SHARE_VM_MEMORY_REFERENCEPOLICY_HPP
  27 
  28 // referencePolicy is used to determine when soft reference objects
  29 // should be cleared.
  30 
  31 
  32 class ReferencePolicy : public CHeapObj<mtGC> {
  33  public:
  34   virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
  35     ShouldNotReachHere();
  36     return true;
  37   }
  38 
  39   // Capture state (of-the-VM) information needed to evaluate the policy
  40   virtual void setup() { /* do nothing */ }
  41 };
  42 
  43 class NeverClearPolicy : public ReferencePolicy {
  44  public:
  45   virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
  46     return false;
  47   }
  48 };
  49 
  50 class AlwaysClearPolicy : public ReferencePolicy {
  51  public:
  52   virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
  53     return true;
  54   }
  55 };
  56 
  57 class LRUCurrentHeapPolicy : public ReferencePolicy {
  58  private:
  59   jlong _max_interval;
  60 
  61  public:
  62   LRUCurrentHeapPolicy();
  63 
  64   // Capture state (of-the-VM) information needed to evaluate the policy
  65   void setup();
  66   virtual bool should_clear_reference(oop p, jlong timestamp_clock);
  67 };
  68 
  69 class LRUMaxHeapPolicy : public ReferencePolicy {
  70  private:
  71   jlong _max_interval;
  72 
  73  public:
  74   LRUMaxHeapPolicy();
  75 
  76   // Capture state (of-the-VM) information needed to evaluate the policy
  77   void setup();
  78   virtual bool should_clear_reference(oop p, jlong timestamp_clock);
  79 };
  80 
  81 #endif // SHARE_VM_MEMORY_REFERENCEPOLICY_HPP