1 /*
 2  * Copyright (c) 2017, 2020, 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
21  * questions.
22  *
23  */
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 set the mark word to "marked" in order to quickly
71     // identify sample objects during the reachability search from gc roots.
72     assert(!obj->mark().is_marked(), "should only mark an object once");
73     obj->set_mark(markWord::prototype().set_marked());
74     assert(obj->mark().is_marked(), "invariant");
75   }
76 };
77 
78 #endif // SHARE_JFR_LEAKPROFILER_CHAINS_OBJECTSAMPLEMARKER_HPP