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static_resource.hpp
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1 //
2 // Copyright (c) 2020 Vinnie Falco (vinnie.falco@gmail.com)
3 //
4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 //
7 // Official repository: https://github.com/boostorg/json
8 //
9
10 #ifndef BOOST_JSON_STATIC_RESOURCE_HPP
11 #define BOOST_JSON_STATIC_RESOURCE_HPP
12
13 #include <boost/container/pmr/memory_resource.hpp>
14 #include <boost/json/detail/config.hpp>
15 #include <boost/json/is_deallocate_trivial.hpp>
16 #include <cstddef>
17
18 namespace boost {
19 namespace json {
20
21 #ifdef _MSC_VER
22 #pragma warning(push)
23 #pragma warning(disable: 4275) // non dll-interface class used as base for dll-interface class
24 #endif
25
26 //----------------------------------------------------------
27
28 /** A resource using a caller-owned buffer, with a trivial deallocate
29
30 This memory resource is a special-purpose resource
31 that releases allocated memory only when the resource
32 is destroyed (or when @ref release is called).
33 It has a trivial deallocate function; that is, the
34 metafunction @ref is_deallocate_trivial returns `true`.
35 \n
36 The resource is constructed from a caller-owned buffer
37 from which subsequent calls to allocate are apportioned.
38 When a memory request cannot be satisfied from the
39 free bytes remaining in the buffer, the allocation
40 request fails with the exception `std::bad_alloc`.
41 \n
42 @par Example
43
44 This parses a JSON text into a value which uses a local
45 stack buffer, then prints the result.
46
47 @code
48
49 unsigned char buf[ 4000 ];
50 static_resource mr( buf );
51
52 // Parse the string, using our memory resource
53 value const jv = parse( "[1,2,3]", &mr );
54
55 // Print the JSON
56 std::cout << jv;
57
58 @endcode
59
60 @par Thread Safety
61 Members of the same instance may not be
62 called concurrently.
63
64 @see
65 https://en.wikipedia.org/wiki/Region-based_memory_management
66 */
67 class
68 BOOST_JSON_DECL
69 BOOST_SYMBOL_VISIBLE
70 static_resource final
71 : public container::pmr::memory_resource
72 {
73 void* p_;
74 std::size_t n_;
75 std::size_t size_;
76
77 public:
78 /// Copy constructor (deleted)
79 static_resource(
80 static_resource const&) = delete;
81
82 /// Copy assignment (deleted)
83 static_resource& operator=(
84 static_resource const&) = delete;
85
86 /** Constructor
87
88 This constructs the resource to use the specified
89 buffer for subsequent calls to allocate. When the
90 buffer is exhausted, allocate will throw
91 `std::bad_alloc`.
92
93 @par Complexity
94 Constant.
95
96 @par Exception Safety
97 No-throw guarantee.
98
99 @param buffer The buffer to use.
100 Ownership is not transferred; the caller is
101 responsible for ensuring that the lifetime of
102 the buffer extends until the resource is destroyed.
103
104 @param size The number of valid bytes pointed
105 to by `buffer`.
106 */
107 /** @{ */
108 static_resource(
109 unsigned char* buffer,
110 std::size_t size) noexcept;
111
112 #if defined(__cpp_lib_byte) || defined(BOOST_JSON_DOCS)
113 static_resource(
114 std::byte* buffer,
115 std::size_t size) noexcept
116 : static_resource(reinterpret_cast<
117 unsigned char*>(buffer), size)
118 {
119 }
120 #endif
121 /** @} */
122
123 /** Constructor
124
125 This constructs the resource to use the specified
126 buffer for subsequent calls to allocate. When the
127 buffer is exhausted, allocate will throw
128 `std::bad_alloc`.
129
130 @par Complexity
131 Constant.
132
133 @par Exception Safety
134 No-throw guarantee.
135
136 @param buffer The buffer to use.
137 Ownership is not transferred; the caller is
138 responsible for ensuring that the lifetime of
139 the buffer extends until the resource is destroyed.
140 */
141 /** @{ */
142 template<std::size_t N>
143 explicit
144 3 static_resource(
145 unsigned char(&buffer)[N]) noexcept
146 3 : static_resource(&buffer[0], N)
147 {
148 3 }
149
150 #if defined(__cpp_lib_byte) || defined(BOOST_JSON_DOCS)
151 template<std::size_t N>
152 explicit
153 static_resource(
154 std::byte(&buffer)[N]) noexcept
155 : static_resource(&buffer[0], N)
156 {
157 }
158 #endif
159 /** @} */
160
161 #ifndef BOOST_JSON_DOCS
162 // Safety net for accidental buffer overflows
163 template<std::size_t N>
164 static_resource(
165 unsigned char(&buffer)[N], std::size_t n) noexcept
166 : static_resource(&buffer[0], n)
167 {
168 // If this goes off, check your parameters
169 // closely, chances are you passed an array
170 // thinking it was a pointer.
171 BOOST_ASSERT(n <= N);
172 }
173
174 #ifdef __cpp_lib_byte
175 // Safety net for accidental buffer overflows
176 template<std::size_t N>
177 static_resource(
178 std::byte(&buffer)[N], std::size_t n) noexcept
179 : static_resource(&buffer[0], n)
180 {
181 // If this goes off, check your parameters
182 // closely, chances are you passed an array
183 // thinking it was a pointer.
184 BOOST_ASSERT(n <= N);
185 }
186 #endif
187 #endif
188
189 /** Release all allocated memory.
190
191 This function resets the buffer provided upon
192 construction so that all of the valid bytes are
193 available for subsequent allocation.
194
195 @par Complexity
196 Constant
197
198 @par Exception Safety
199 No-throw guarantee.
200 */
201 void
202 release() noexcept;
203
204 protected:
205 #ifndef BOOST_JSON_DOCS
206 void*
207 do_allocate(
208 std::size_t n,
209 std::size_t align) override;
210
211 void
212 do_deallocate(
213 void* p,
214 std::size_t n,
215 std::size_t align) override;
216
217 bool
218 do_is_equal(
219 memory_resource const& mr
220 ) const noexcept override;
221 #endif
222 };
223
224 #ifdef _MSC_VER
225 #pragma warning(pop)
226 #endif
227
228 template<>
229 struct is_deallocate_trivial<
230 static_resource>
231 {
232 static constexpr bool value = true;
233 };
234
235 } // namespace json
236 } // namespace boost
237
238 #endif
239