text: /*
   * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
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   */
  
  #ifndef SHARE_JFR_LEAKPROFILER_CHAINS_OBJECTSAMPLEMARKER_HPP
  #define SHARE_JFR_LEAKPROFILER_CHAINS_OBJECTSAMPLEMARKER_HPP
  
  #include "memory/allocation.hpp"
  #include "oops/markOop.hpp"
  #include "utilities/growableArray.hpp"
  //
  // This class will save the original mark oop of a object sample object.
  // It will then install an "identifier" mark oop to be used for
  // identification purposes in the search for reference chains.
  // The destructor will restore each modified oop with its original mark oop.
  //
  class ObjectSampleMarker : public StackObj {
   private:
    class ObjectSampleMarkOop : public ResourceObj {
      friend class ObjectSampleMarker;
     private:
      oop _obj;
      markOop _mark_oop;
      ObjectSampleMarkOop(const oop obj,
                          const markOop mark_oop) : _obj(obj),
                                                    _mark_oop(mark_oop) {}
     public:
      ObjectSampleMarkOop() : _obj(NULL), _mark_oop(NULL) {}
    };
  
    GrowableArray<ObjectSampleMarkOop>* _store;
  
   public:
    ObjectSampleMarker() :
         _store(new GrowableArray<ObjectSampleMarkOop>(16)) {}
    ~ObjectSampleMarker() {
      assert(_store != NULL, "invariant");
      // restore the saved, original, markOop for sample objects
      while (_store->is_nonempty()) {
        ObjectSampleMarkOop sample_oop = _store->pop();
        sample_oop._obj->set_mark(sample_oop._mark_oop);
        assert(sample_oop._obj->mark() == sample_oop._mark_oop, "invariant");
      }
    }
  
    void mark(oop obj) {
      assert(obj != NULL, "invariant");
      // save the original markOop
      _store->push(ObjectSampleMarkOop(obj, obj->mark()));
      // now we will "poison" the mark word of the sample object
      // to the intermediate monitor INFLATING state.
      // This is an "impossible" state during a safepoint,
      // hence we will use it to quickly identify sample objects
      // during the reachability search from gc roots.
      assert(NULL == markOopDesc::INFLATING(), "invariant");
      obj->set_mark(markOopDesc::INFLATING());
      assert(NULL == obj->mark(), "invariant");
    }
  };
  
  #endif // SHARE_JFR_LEAKPROFILER_CHAINS_OBJECTSAMPLEMARKER_HPP
  