| 1 | /* Reference-counted smart pointer class |
| 2 | |
| 3 | Copyright (C) 2016-2020 Free Software Foundation, Inc. |
| 4 | |
| 5 | This file is part of GDB. |
| 6 | |
| 7 | This program is free software; you can redistribute it and/or modify |
| 8 | it under the terms of the GNU General Public License as published by |
| 9 | the Free Software Foundation; either version 3 of the License, or |
| 10 | (at your option) any later version. |
| 11 | |
| 12 | This program is distributed in the hope that it will be useful, |
| 13 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 15 | GNU General Public License for more details. |
| 16 | |
| 17 | You should have received a copy of the GNU General Public License |
| 18 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ |
| 19 | |
| 20 | #ifndef COMMON_GDB_REF_PTR_H |
| 21 | #define COMMON_GDB_REF_PTR_H |
| 22 | |
| 23 | #include <cstddef> |
| 24 | |
| 25 | namespace gdb |
| 26 | { |
| 27 | |
| 28 | /* An instance of this class either holds a reference to a |
| 29 | reference-counted object or is "NULL". Reference counting is |
| 30 | handled externally by a policy class. If the object holds a |
| 31 | reference, then when the object is destroyed, the reference is |
| 32 | decref'd. |
| 33 | |
| 34 | Normally an instance is constructed using a pointer. This sort of |
| 35 | initialization lets this class manage the lifetime of that |
| 36 | reference. |
| 37 | |
| 38 | Assignment and copy construction will make a new reference as |
| 39 | appropriate. Assignment from a plain pointer is disallowed to |
| 40 | avoid confusion about whether this acquires a new reference; |
| 41 | instead use the "reset" method -- which, like the pointer |
| 42 | constructor, transfers ownership. |
| 43 | |
| 44 | The policy class must provide two static methods: |
| 45 | void incref (T *); |
| 46 | void decref (T *); |
| 47 | */ |
| 48 | template<typename T, typename Policy> |
| 49 | class ref_ptr |
| 50 | { |
| 51 | public: |
| 52 | |
| 53 | /* Create a new NULL instance. */ |
| 54 | ref_ptr () |
| 55 | : m_obj (NULL) |
| 56 | { |
| 57 | } |
| 58 | |
| 59 | /* Create a new NULL instance. Note that this is not explicit. */ |
| 60 | ref_ptr (const std::nullptr_t) |
| 61 | : m_obj (NULL) |
| 62 | { |
| 63 | } |
| 64 | |
| 65 | /* Create a new instance. OBJ is a reference, management of which |
| 66 | is now transferred to this class. */ |
| 67 | explicit ref_ptr (T *obj) |
| 68 | : m_obj (obj) |
| 69 | { |
| 70 | } |
| 71 | |
| 72 | /* Copy another instance. */ |
| 73 | ref_ptr (const ref_ptr &other) |
| 74 | : m_obj (other.m_obj) |
| 75 | { |
| 76 | if (m_obj != NULL) |
| 77 | Policy::incref (m_obj); |
| 78 | } |
| 79 | |
| 80 | /* Transfer ownership from OTHER. */ |
| 81 | ref_ptr (ref_ptr &&other) |
| 82 | : m_obj (other.m_obj) |
| 83 | { |
| 84 | other.m_obj = NULL; |
| 85 | } |
| 86 | |
| 87 | /* Destroy this instance. */ |
| 88 | ~ref_ptr () |
| 89 | { |
| 90 | if (m_obj != NULL) |
| 91 | Policy::decref (m_obj); |
| 92 | } |
| 93 | |
| 94 | /* Copy another instance. */ |
| 95 | ref_ptr &operator= (const ref_ptr &other) |
| 96 | { |
| 97 | /* Do nothing on self-assignment. */ |
| 98 | if (this != &other) |
| 99 | { |
| 100 | reset (other.m_obj); |
| 101 | if (m_obj != NULL) |
| 102 | Policy::incref (m_obj); |
| 103 | } |
| 104 | return *this; |
| 105 | } |
| 106 | |
| 107 | /* Transfer ownership from OTHER. */ |
| 108 | ref_ptr &operator= (ref_ptr &&other) |
| 109 | { |
| 110 | /* Do nothing on self-assignment. */ |
| 111 | if (this != &other) |
| 112 | { |
| 113 | reset (other.m_obj); |
| 114 | other.m_obj = NULL; |
| 115 | } |
| 116 | return *this; |
| 117 | } |
| 118 | |
| 119 | /* Change this instance's referent. OBJ is a reference, management |
| 120 | of which is now transferred to this class. */ |
| 121 | void reset (T *obj) |
| 122 | { |
| 123 | if (m_obj != NULL) |
| 124 | Policy::decref (m_obj); |
| 125 | m_obj = obj; |
| 126 | } |
| 127 | |
| 128 | /* Return this instance's referent without changing the state of |
| 129 | this class. */ |
| 130 | T *get () const |
| 131 | { |
| 132 | return m_obj; |
| 133 | } |
| 134 | |
| 135 | /* Return this instance's referent, and stop managing this |
| 136 | reference. The caller is now responsible for the ownership of |
| 137 | the reference. */ |
| 138 | ATTRIBUTE_UNUSED_RESULT T *release () |
| 139 | { |
| 140 | T *result = m_obj; |
| 141 | |
| 142 | m_obj = NULL; |
| 143 | return result; |
| 144 | } |
| 145 | |
| 146 | /* Let users refer to members of the underlying pointer. */ |
| 147 | T *operator-> () const |
| 148 | { |
| 149 | return m_obj; |
| 150 | } |
| 151 | |
| 152 | /* Acquire a new reference and return a ref_ptr that owns it. */ |
| 153 | static ref_ptr<T, Policy> new_reference (T *obj) |
| 154 | { |
| 155 | Policy::incref (obj); |
| 156 | return ref_ptr<T, Policy> (obj); |
| 157 | } |
| 158 | |
| 159 | private: |
| 160 | |
| 161 | T *m_obj; |
| 162 | }; |
| 163 | |
| 164 | template<typename T, typename Policy> |
| 165 | inline bool operator== (const ref_ptr<T, Policy> &lhs, |
| 166 | const ref_ptr<T, Policy> &rhs) |
| 167 | { |
| 168 | return lhs.get () == rhs.get (); |
| 169 | } |
| 170 | |
| 171 | template<typename T, typename Policy> |
| 172 | inline bool operator== (const ref_ptr<T, Policy> &lhs, const T *rhs) |
| 173 | { |
| 174 | return lhs.get () == rhs; |
| 175 | } |
| 176 | |
| 177 | template<typename T, typename Policy> |
| 178 | inline bool operator== (const ref_ptr<T, Policy> &lhs, const std::nullptr_t) |
| 179 | { |
| 180 | return lhs.get () == nullptr; |
| 181 | } |
| 182 | |
| 183 | template<typename T, typename Policy> |
| 184 | inline bool operator== (const T *lhs, const ref_ptr<T, Policy> &rhs) |
| 185 | { |
| 186 | return lhs == rhs.get (); |
| 187 | } |
| 188 | |
| 189 | template<typename T, typename Policy> |
| 190 | inline bool operator== (const std::nullptr_t, const ref_ptr<T, Policy> &rhs) |
| 191 | { |
| 192 | return nullptr == rhs.get (); |
| 193 | } |
| 194 | |
| 195 | template<typename T, typename Policy> |
| 196 | inline bool operator!= (const ref_ptr<T, Policy> &lhs, |
| 197 | const ref_ptr<T, Policy> &rhs) |
| 198 | { |
| 199 | return lhs.get () != rhs.get (); |
| 200 | } |
| 201 | |
| 202 | template<typename T, typename Policy> |
| 203 | inline bool operator!= (const ref_ptr<T, Policy> &lhs, const T *rhs) |
| 204 | { |
| 205 | return lhs.get () != rhs; |
| 206 | } |
| 207 | |
| 208 | template<typename T, typename Policy> |
| 209 | inline bool operator!= (const ref_ptr<T, Policy> &lhs, const std::nullptr_t) |
| 210 | { |
| 211 | return lhs.get () != nullptr; |
| 212 | } |
| 213 | |
| 214 | template<typename T, typename Policy> |
| 215 | inline bool operator!= (const T *lhs, const ref_ptr<T, Policy> &rhs) |
| 216 | { |
| 217 | return lhs != rhs.get (); |
| 218 | } |
| 219 | |
| 220 | template<typename T, typename Policy> |
| 221 | inline bool operator!= (const std::nullptr_t, const ref_ptr<T, Policy> &rhs) |
| 222 | { |
| 223 | return nullptr != rhs.get (); |
| 224 | } |
| 225 | |
| 226 | } |
| 227 | |
| 228 | #endif /* COMMON_GDB_REF_PTR_H */ |