1 /*
   2  * Copyright (c) 2017, 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.
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   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
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  24 
  25 #ifndef SHARE_JFR_LEAKPROFILER_CHAINS_OBJECTSAMPLEMARKER_HPP
  26 #define SHARE_JFR_LEAKPROFILER_CHAINS_OBJECTSAMPLEMARKER_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "oops/markWord.hpp"
  30 #include "utilities/growableArray.hpp"
  31 //
  32 // This class will save the original mark oop of a object sample object.
  33 // It will then install an "identifier" mark oop to be used for
  34 // identification purposes in the search for reference chains.
  35 // The destructor will restore each modified oop with its original mark oop.
  36 //
  37 class ObjectSampleMarker : public StackObj {
  38  private:
  39   class ObjectSampleMarkWord : public ResourceObj {
  40     friend class ObjectSampleMarker;
  41    private:
  42     oop _obj;
  43     markWord _mark_word;
  44     ObjectSampleMarkWord(const oop obj,
  45                          const markWord mark_word) : _obj(obj),
  46                                                      _mark_word(mark_word) {}
  47    public:
  48     ObjectSampleMarkWord() : _obj(NULL), _mark_word(markWord::zero()) {}
  49   };
  50 
  51   GrowableArray<ObjectSampleMarkWord>* _store;
  52 
  53  public:
  54   ObjectSampleMarker() :
  55        _store(new GrowableArray<ObjectSampleMarkWord>(16)) {}
  56   ~ObjectSampleMarker() {
  57     assert(_store != NULL, "invariant");
  58     // restore the saved, original, markWord for sample objects
  59     while (_store->is_nonempty()) {
  60       ObjectSampleMarkWord sample_oop = _store->pop();
  61       sample_oop._obj->set_mark(sample_oop._mark_word);
  62       assert(sample_oop._obj->mark() == sample_oop._mark_word, "invariant");
  63     }
  64   }
  65 
  66   void mark(oop obj) {
  67     assert(obj != NULL, "invariant");
  68     // save the original markWord
  69     _store->push(ObjectSampleMarkWord(obj, obj->mark()));
  70     // now we will "poison" the mark word of the sample object
  71     // to the intermediate monitor INFLATING state.
  72     // This is an "impossible" state during a safepoint,
  73     // hence we will use it to quickly identify sample objects
  74     // during the reachability search from gc roots.
  75     assert(NULL == markWord::INFLATING().to_pointer(), "invariant");
  76     obj->set_mark(markWord::INFLATING());
  77     assert(NULL == obj->mark().to_pointer(), "invariant");
  78   }
  79 };
  80 
  81 #endif // SHARE_JFR_LEAKPROFILER_CHAINS_OBJECTSAMPLEMARKER_HPP