1 /* 2 * Copyright (c) 2017, 2018, 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_VM_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP 26 #define SHARE_VM_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP 27 28 #include "jfr/utilities/jfrAllocation.hpp" 29 #include "runtime/atomic.hpp" 30 31 template <typename T> 32 class RefCountHandle { 33 template <typename, typename> 34 friend class RefCountPointer; 35 private: 36 const T* _ptr; 37 38 RefCountHandle(const T* ptr) : _ptr(ptr) { 39 assert(_ptr != NULL, "invariant"); 40 _ptr->add_ref(); 41 } 42 43 public: 44 RefCountHandle() : _ptr(NULL) {} 45 46 RefCountHandle(const RefCountHandle<T>& rhs) : _ptr(rhs._ptr) { 47 if (_ptr != NULL) { 48 _ptr->add_ref(); 49 } 50 } 51 52 ~RefCountHandle() { 53 if (_ptr != NULL) { 54 const T* temp = _ptr; 55 _ptr = NULL; 56 temp->remove_ref(); 57 } 58 } 59 60 // The copy-and-swap idiom upholds reference counting semantics 61 void operator=(RefCountHandle<T> rhs) { 62 const T* temp = rhs._ptr; 63 rhs._ptr = _ptr; 64 _ptr = temp; 65 } 66 67 bool operator==(const RefCountHandle<T>& rhs) const { 68 return _ptr == rhs._ptr; 69 } 70 71 bool operator!=(const RefCountHandle<T>& rhs) const { 72 return !operator==(rhs); 73 } 74 75 bool valid() const { 76 return _ptr != NULL; 77 } 78 79 const T & operator->() const { 80 return *_ptr; 81 } 82 83 T& operator->() { 84 return *const_cast<T*>(_ptr); 85 } 86 }; 87 88 class MultiThreadedRefCounter { 89 private: 90 mutable volatile int _refs; 91 public: 92 MultiThreadedRefCounter() : _refs(0) {} 93 94 void inc() const { 95 Atomic::add(1, &_refs); 96 } 97 98 bool dec() const { 99 return 0 == Atomic::add((-1), &_refs); 100 } 101 102 int current() const { 103 return _refs; 104 } 105 }; 106 107 template <typename T, typename RefCountImpl = MultiThreadedRefCounter> 108 class RefCountPointer : public JfrCHeapObj { 109 template <typename> 110 friend class RefCountHandle; 111 typedef RefCountHandle<RefCountPointer<T, RefCountImpl> > RefHandle; 112 private: 113 const T* _ptr; 114 mutable RefCountImpl _refs; 115 116 // disallow multiple copies 117 RefCountPointer(const RefCountPointer<T, RefCountImpl>& rhs); 118 void operator=(const RefCountPointer<T, RefCountImpl>& rhs); 119 120 ~RefCountPointer() { 121 assert(_refs.current() == 0, "invariant"); 122 delete const_cast<T*>(_ptr); 123 } 124 125 void add_ref() const { 126 _refs.inc(); 127 } 128 129 void remove_ref() const { 130 if (_refs.dec()) { 131 delete this; 132 } 133 } 134 135 RefCountPointer(const T* ptr) : _ptr(ptr), _refs() { 136 assert(_ptr != NULL, "invariant"); 137 } 138 139 public: 140 const T* operator->() const { 141 return _ptr; 142 } 143 144 T* operator->() { 145 return const_cast<T*>(_ptr); 146 } 147 148 static RefHandle make(const T* ptr) { 149 assert(ptr != NULL, "invariant"); 150 return RefHandle(new RefCountPointer<T, RefCountImpl>(ptr)); 151 } 152 }; 153 154 #endif // SHARE_VM_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP