MySQL  8.0.27
Source Code Documentation
stateless_allocator.h
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22 
23 #ifndef STATELESS_ALLOCATOR_INCLUDED
24 #define STATELESS_ALLOCATOR_INCLUDED
25 
26 #include <assert.h>
27 #include <stddef.h>
28 #include <limits>
29 #include <new>
30 #include <utility> // std::forward
31 
32 #include "my_compiler.h"
33 
34 /**
35  Functor struct which invokes my_free. Declared here as it is used as the
36  defalt value for Stateless_allocator's DEALLOC_FUN template parameter.
37 */
39  void operator()(void *p, size_t) const;
40 };
41 
42 /**
43  Stateless_allocator is a C++ STL memory allocator skeleton based on
44  Malloc_allocator, which assumes that a global free function can be
45  used to allocate and deallocate memory, so that no state need to be
46  kept by the allocator object.
47 
48  The allocation and deallocation functions must be provided as
49  callable types (aka functors) which have no state and can be default
50  constructed.
51 
52  Example usage:
53 
54  @verbatim
55  struct My_psi_key_alloc
56  {
57  void* operator(size_t s)()
58  {
59  return my_malloc(My_psi_key, s, MYF(MY_WME | ME_FATALERROR));
60  }
61  };
62 
63  template <class T>
64  using My_psi_key_allocator =
65  Stateless_allocator<T, My_psi_key_alloc>;
66 
67  template < template<class T> class Allocator >
68  using default_string=
69  std::basic_string<char, std::char_traits<char>, Allocator<char> >;
70 
71 
72  typedef default_string<My_psi_key_allocator> My_psi_key_str;
73 
74  My_psi_key_str x("foobar");
75  @endverbatim
76 
77  Since a Stateless_allocator instance is always
78  default-constructible, it can also be used to create instances of
79  std::basic_string, even with compilers that have this libstd++ bug:
80  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56437 "basic_string
81  assumes that allocators are default-constructible".
82 
83  @note allocate() throws std::bad_alloc() similarly to the default
84  STL memory allocator. This is necessary - STL functions which allocate
85  memory expect it. Otherwise these functions will try to use the memory,
86  leading to seg faults if memory allocation was not successful.
87 
88 */
89 
90 template <class T, class ALLOC_FUN, class DEALLOC_FUN = My_free_functor>
92  public:
93  typedef T value_type;
94  typedef size_t size_type;
95  typedef ptrdiff_t difference_type;
96 
97  typedef T *pointer;
98  typedef const T *const_pointer;
99 
100  typedef T &reference;
101  typedef const T &const_reference;
102 
103  template <class T_>
106 
107  Stateless_allocator() = default;
108 
109  pointer address(reference r) const { return &r; }
111 
112  template <class U>
114 
115  template <class U>
117 
118  pointer allocate(size_type n, const_pointer hint [[maybe_unused]] = nullptr) {
119  if (n == 0) return nullptr;
120  if (n > max_size()) throw std::bad_alloc();
121 
122  pointer p = static_cast<pointer>(ALLOC_FUN()(n * sizeof(T)));
123  if (p == nullptr) throw std::bad_alloc();
124  return p;
125  }
126 
127  void deallocate(pointer p, size_type n) { DEALLOC_FUN()(p, n); }
128 
129  template <class U, class... Args>
130  void construct(U *p, Args &&... args) {
131  assert(p != nullptr);
132  try {
133  ::new ((void *)p) U(std::forward<Args>(args)...);
134  } catch (...) {
135  assert(false); // Constructor should not throw an exception.
136  }
137  }
138 
139  void destroy(pointer p) {
140  assert(p != nullptr);
141  try {
142  p->~T();
143  } catch (...) {
144  assert(false); // Destructor should not throw an exception
145  }
146  }
147 
148  size_type max_size() const {
149  return std::numeric_limits<size_t>::max() / sizeof(T);
150  }
151 
152  template <class U>
153  struct rebind {
155  };
156 };
157 
158 template <class T, class ALLOC_FUN, class DEALLOC_FUN>
161  return true;
162 }
163 
164 template <class T, class ALLOC_FUN, class DEALLOC_FUN>
167  return false;
168 }
169 
170 #endif // STATELESS_ALLOCATOR_INCLUDED
Stateless_allocator is a C++ STL memory allocator skeleton based on Malloc_allocator,...
Definition: stateless_allocator.h:91
Stateless_allocator & operator=(const Stateless_allocator_type< U > &)
Definition: stateless_allocator.h:116
ptrdiff_t difference_type
Definition: stateless_allocator.h:95
T * pointer
Definition: stateless_allocator.h:97
Stateless_allocator(const Stateless_allocator_type< U > &)
Definition: stateless_allocator.h:113
size_t size_type
Definition: stateless_allocator.h:94
T value_type
Definition: stateless_allocator.h:93
void construct(U *p, Args &&... args)
Definition: stateless_allocator.h:130
pointer allocate(size_type n, const_pointer hint[[maybe_unused]]=nullptr)
Definition: stateless_allocator.h:118
pointer address(reference r) const
Definition: stateless_allocator.h:109
const_pointer address(const_reference r) const
Definition: stateless_allocator.h:110
void deallocate(pointer p, size_type n)
Definition: stateless_allocator.h:127
const T & const_reference
Definition: stateless_allocator.h:101
const T * const_pointer
Definition: stateless_allocator.h:98
void destroy(pointer p)
Definition: stateless_allocator.h:139
Stateless_allocator()=default
T & reference
Definition: stateless_allocator.h:100
size_type max_size() const
Definition: stateless_allocator.h:148
const char * p
Definition: ctype-mb.cc:1236
#define U
Definition: ctype-tis620.cc:74
Header for compiler-dependent features.
const mysql_service_registry_t * r
Definition: pfs_example_plugin_employee.cc:85
bool operator==(const Stateless_allocator< T, ALLOC_FUN, DEALLOC_FUN > &, const Stateless_allocator< T, ALLOC_FUN, DEALLOC_FUN > &)
Definition: stateless_allocator.h:159
bool operator!=(const Stateless_allocator< T, ALLOC_FUN, DEALLOC_FUN > &, const Stateless_allocator< T, ALLOC_FUN, DEALLOC_FUN > &)
Definition: stateless_allocator.h:165
Functor struct which invokes my_free.
Definition: stateless_allocator.h:38
void operator()(void *p, size_t) const
Definition: stateless_allocator.cc:27
Definition: stateless_allocator.h:153
Stateless_allocator< U, ALLOC_FUN, DEALLOC_FUN > other
Definition: stateless_allocator.h:154
Definition: dtoa.cc:594
int n
Definition: xcom_base.cc:505