MySQL 8.0.29
Source Code Documentation
mem_root_allocator.h
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15 but WITHOUT ANY WARRANTY; without even the implied warranty of
16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 GNU General Public License, version 2.0, for more details.
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20 along with this program; if not, write to the Free Software
21 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
22
23#ifndef MEM_ROOT_ALLOCATOR_INCLUDED
24#define MEM_ROOT_ALLOCATOR_INCLUDED
25
26#include <assert.h>
27#include <limits>
28#include <new>
29#include <utility> // std::forward
30
31#include "my_alloc.h"
32
33/**
34 Mem_root_allocator is a C++ STL memory allocator based on MEM_ROOT.
35
36 No deallocation is done by this allocator. Calling the constructor
37 and destructor on the supplied MEM_ROOT is the responsibility of
38 the caller. Do *not* call Clear() or ~MEM_ROOT until the destructor
39 of any objects using this allocator has completed. This includes iterators.
40
41 Example of use:
42 vector<int, Mem_root_allocator<int> > v((Mem_root_allocator<int>(&mem_root)));
43
44 @note allocate() throws std::bad_alloc() similarly to the default
45 STL memory allocator. This is necessary - STL functions which allocate
46 memory expect it. Otherwise these functions will try to use the memory,
47 leading to seg faults if memory allocation was not successful.
48
49 @note This allocator cannot be used for std::basic_string with RHEL 6/7
50 because of this bug:
51 https://bugzilla.redhat.com/show_bug.cgi?id=1546704
52 "Define _GLIBCXX_USE_CXX11_ABI gets ignored by gcc in devtoolset-7"
53
54 @note C++98 says that STL implementors can assume that allocator objects
55 of the same type always compare equal. This will only be the case for
56 two Mem_root_allocators that use the same MEM_ROOT. Care should be taken
57 when this is not the case. Especially:
58 - Using list::splice() on two lists with allocators using two different
59 MEM_ROOTs causes undefined behavior. Most implementations seem to give
60 runtime errors in such cases.
61 - swap() on two collections with allocators using two different MEM_ROOTs
62 is not well defined. At least some implementations also swap allocators,
63 but this should not be depended on.
64*/
65
66template <class T>
68 // This cannot be const if we want to be able to swap.
70
71 public:
72 typedef T value_type;
73 typedef size_t size_type;
74 typedef ptrdiff_t difference_type;
75
76 typedef T *pointer;
77 typedef const T *const_pointer;
78
79 typedef T &reference;
80 typedef const T &const_reference;
81
82 pointer address(reference r) const { return &r; }
84
86
88
89 template <class U>
91 : m_memroot(other.memroot()) {}
92
93 template <class U>
95 [[maybe_unused]]) {
96 assert(m_memroot == other.memroot()); // Don't swap memroot.
97 }
98
99 pointer allocate(size_type n, const_pointer hint [[maybe_unused]] = nullptr) {
100 if (n == 0) return nullptr;
101 if (n > max_size()) throw std::bad_alloc();
102
103 pointer p = static_cast<pointer>(m_memroot->Alloc(n * sizeof(T)));
104 if (p == nullptr) throw std::bad_alloc();
105 return p;
106 }
107
109
110 template <class U, class... Args>
111 void construct(U *p, Args &&... args) {
112 assert(p != nullptr);
113 try {
114 ::new ((void *)p) U(std::forward<Args>(args)...);
115 } catch (...) {
116 assert(false); // Constructor should not throw an exception.
117 }
118 }
119
121 assert(p != nullptr);
122 try {
123 p->~T();
124 } catch (...) {
125 assert(false); // Destructor should not throw an exception
126 }
127 }
128
130 return std::numeric_limits<size_t>::max() / sizeof(T);
131 }
132
133 template <class U>
134 struct rebind {
136 };
137
138 MEM_ROOT *memroot() const { return m_memroot; }
139};
140
141template <class T>
143 const Mem_root_allocator<T> &a2) {
144 return a1.memroot() == a2.memroot();
145}
146
147template <class T>
149 const Mem_root_allocator<T> &a2) {
150 return a1.memroot() != a2.memroot();
151}
152
153#endif // MEM_ROOT_ALLOCATOR_INCLUDED
Mem_root_allocator is a C++ STL memory allocator based on MEM_ROOT.
Definition: mem_root_allocator.h:67
const T * const_pointer
Definition: mem_root_allocator.h:77
MEM_ROOT * m_memroot
Definition: mem_root_allocator.h:69
Mem_root_allocator()
Definition: mem_root_allocator.h:87
Mem_root_allocator(MEM_ROOT *memroot)
Definition: mem_root_allocator.h:85
pointer allocate(size_type n, const_pointer hint=nullptr)
Definition: mem_root_allocator.h:99
size_t size_type
Definition: mem_root_allocator.h:73
pointer address(reference r) const
Definition: mem_root_allocator.h:82
const_pointer address(const_reference r) const
Definition: mem_root_allocator.h:83
T & reference
Definition: mem_root_allocator.h:79
size_type max_size() const
Definition: mem_root_allocator.h:129
Mem_root_allocator & operator=(const Mem_root_allocator< U > &other)
Definition: mem_root_allocator.h:94
Mem_root_allocator(const Mem_root_allocator< U > &other)
Definition: mem_root_allocator.h:90
ptrdiff_t difference_type
Definition: mem_root_allocator.h:74
T value_type
Definition: mem_root_allocator.h:72
const T & const_reference
Definition: mem_root_allocator.h:80
void deallocate(pointer, size_type)
Definition: mem_root_allocator.h:108
void destroy(pointer p)
Definition: mem_root_allocator.h:120
void construct(U *p, Args &&... args)
Definition: mem_root_allocator.h:111
T * pointer
Definition: mem_root_allocator.h:76
MEM_ROOT * memroot() const
Definition: mem_root_allocator.h:138
const char * p
Definition: ctype-mb.cc:1236
#define U
Definition: ctype-tis620.cc:74
Fido Client Authentication nullptr
Definition: fido_client_plugin.cc:221
bool operator==(const Mem_root_allocator< T > &a1, const Mem_root_allocator< T > &a2)
Definition: mem_root_allocator.h:142
bool operator!=(const Mem_root_allocator< T > &a1, const Mem_root_allocator< T > &a2)
Definition: mem_root_allocator.h:148
This file follows Google coding style, except for the name MEM_ROOT (which is kept for historical rea...
const mysql_service_registry_t * r
Definition: pfs_example_plugin_employee.cc:85
The MEM_ROOT is a simple arena, where allocations are carved out of larger blocks.
Definition: my_alloc.h:82
void * Alloc(size_t length)
Allocate memory.
Definition: my_alloc.h:144
Definition: mem_root_allocator.h:134
Mem_root_allocator< U > other
Definition: mem_root_allocator.h:135
Definition: dtoa.cc:594
int n
Definition: xcom_base.cc:505