1 /*
   2  * Copyright (c) 2000, 2015, 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
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  24 
  25 #ifndef SHARE_VM_GC_SHARED_REFERENCEPOLICY_HPP
  26 #define SHARE_VM_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:
  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
  42   virtual void setup() { /* do nothing */ }
  43 };
  44 
  45 class NeverClearPolicy : public ReferencePolicy {
  46  public:
  47   virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
  48     return false;
  49   }
  50 };
  51 
  52 class AlwaysClearPolicy : public ReferencePolicy {
  53  public:
  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_VM_GC_SHARED_REFERENCEPOLICY_HPP