1 /*
 2  * Copyright (c) 2017, 2024, 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
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17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18  *
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24 
25 #ifndef SHARE_OOPS_OOPHANDLE_HPP
26 #define SHARE_OOPS_OOPHANDLE_HPP
27 
28 #include "metaprogramming/primitiveConversions.hpp"
29 #include "oops/oopsHierarchy.hpp"
30 
31 #include <type_traits>
32 
33 class OopStorage;
34 
35 // Simple classes for wrapping oop and atomically accessed oop pointers
36 // stored in OopStorage, or stored in the ClassLoaderData handles area.
37 // These classes help with allocation, release, and NativeAccess loads and
38 // stores with the appropriate barriers.
39 
40 class OopHandle {
41   friend class VMStructs;
42 private:
43   oop* _obj;
44 
45 public:
46   OopHandle() : _obj(nullptr) {}
47   explicit OopHandle(oop* w) : _obj(w) {}
48   OopHandle(OopStorage* storage, oop obj);
49 
50   OopHandle(const OopHandle& copy) : _obj(copy._obj) {}
51 
52   OopHandle& operator=(const OopHandle& copy) {
53     // Allow "this" to be junk if copy is empty; needed by initialization of
54     // raw memory in hashtables.
55     assert(is_empty() || copy.is_empty(), "can only copy if empty");
56     _obj = copy._obj;
57     return *this;
58   }
59 
60   void swap(OopHandle& copy) {
61     ::swap(_obj, copy._obj);
62   }
63 
64   inline oop resolve() const;
65   inline oop peek() const;
66 
67   bool is_empty() const { return _obj == nullptr; }
68 
69   inline void release(OopStorage* storage);
70 
71   inline void replace(oop obj);
72 
73   inline oop xchg(oop new_value);
74   inline oop cmpxchg(oop old_value, oop new_value);
75 
76   oop* ptr_raw() const { return _obj; }
77 };
78 
79 #endif // SHARE_OOPS_OOPHANDLE_HPP