/*

 * 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.

 *

 */

#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");

  }

};