MySQL  8.0.23
Source Code Documentation
stateless_allocator.h
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22 
23 #ifndef STATELESS_ALLOCATOR_INCLUDED
24 #define STATELESS_ALLOCATOR_INCLUDED
25 
26 #include <stddef.h>
27 #include <limits>
28 #include <new>
29 #include <utility> // std::forward
30 
31 #include "my_compiler.h"
32 #include "my_dbug.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 
119  const_pointer hint MY_ATTRIBUTE((unused)) = nullptr) {
120  if (n == 0) return nullptr;
121  if (n > max_size()) throw std::bad_alloc();
122 
123  pointer p = static_cast<pointer>(ALLOC_FUN()(n * sizeof(T)));
124  if (p == nullptr) throw std::bad_alloc();
125  return p;
126  }
127 
128  void deallocate(pointer p, size_type n) { DEALLOC_FUN()(p, n); }
129 
130  template <class U, class... Args>
131  void construct(U *p, Args &&... args) {
132  DBUG_ASSERT(p != nullptr);
133  try {
134  ::new ((void *)p) U(std::forward<Args>(args)...);
135  } catch (...) {
136  DBUG_ASSERT(false); // Constructor should not throw an exception.
137  }
138  }
139 
140  void destroy(pointer p) {
141  DBUG_ASSERT(p != nullptr);
142  try {
143  p->~T();
144  } catch (...) {
145  DBUG_ASSERT(false); // Destructor should not throw an exception
146  }
147  }
148 
149  size_type max_size() const {
150  return std::numeric_limits<size_t>::max() / sizeof(T);
151  }
152 
153  template <class U>
154  struct rebind {
156  };
157 };
158 
159 template <class T, class ALLOC_FUN, class DEALLOC_FUN>
162  return true;
163 }
164 
165 template <class T, class ALLOC_FUN, class DEALLOC_FUN>
168  return false;
169 }
170 
171 #endif // STATELESS_ALLOCATOR_INCLUDED
Stateless_allocator::allocate
pointer allocate(size_type n, const_pointer hint=nullptr)
Definition: stateless_allocator.h:118
Stateless_allocator::const_pointer
const T * const_pointer
Definition: stateless_allocator.h:98
Stateless_allocator
Stateless_allocator is a C++ STL memory allocator skeleton based on Malloc_allocator,...
Definition: stateless_allocator.h:91
Stateless_allocator::pointer
T * pointer
Definition: stateless_allocator.h:97
Stateless_allocator::size_type
size_t size_type
Definition: stateless_allocator.h:94
my_compiler.h
Stateless_allocator::max_size
size_type max_size() const
Definition: stateless_allocator.h:149
my_dbug.h
operator==
bool operator==(const Stateless_allocator< T, ALLOC_FUN, DEALLOC_FUN > &, const Stateless_allocator< T, ALLOC_FUN, DEALLOC_FUN > &)
Definition: stateless_allocator.h:160
Stateless_allocator::address
const_pointer address(const_reference r) const
Definition: stateless_allocator.h:110
Stateless_allocator::rebind
Definition: stateless_allocator.h:154
U
#define U
Definition: ctype-tis620.cc:74
Stateless_allocator::reference
T & reference
Definition: stateless_allocator.h:100
n
int n
Definition: xcom_base.cc:445
U
Definition: dtoa.cc:601
r
const mysql_service_registry_t * r
Definition: pfs_example_plugin_employee.cc:85
Stateless_allocator::difference_type
ptrdiff_t difference_type
Definition: stateless_allocator.h:95
Stateless_allocator::deallocate
void deallocate(pointer p, size_type n)
Definition: stateless_allocator.h:128
operator!=
bool operator!=(const Stateless_allocator< T, ALLOC_FUN, DEALLOC_FUN > &, const Stateless_allocator< T, ALLOC_FUN, DEALLOC_FUN > &)
Definition: stateless_allocator.h:166
Stateless_allocator::value_type
T value_type
Definition: stateless_allocator.h:93
Stateless_allocator::const_reference
const T & const_reference
Definition: stateless_allocator.h:101
Stateless_allocator::destroy
void destroy(pointer p)
Definition: stateless_allocator.h:140
Stateless_allocator::construct
void construct(U *p, Args &&... args)
Definition: stateless_allocator.h:131
Stateless_allocator::Stateless_allocator
Stateless_allocator()=default
DBUG_ASSERT
#define DBUG_ASSERT(A)
Definition: my_dbug.h:199
Stateless_allocator::Stateless_allocator
Stateless_allocator(const Stateless_allocator_type< U > &)
Definition: stateless_allocator.h:113
My_free_functor::operator()
void operator()(void *p, size_t) const
Definition: stateless_allocator.cc:27
Stateless_allocator::operator=
Stateless_allocator & operator=(const Stateless_allocator_type< U > &)
Definition: stateless_allocator.h:116
My_free_functor
Functor struct which invokes my_free.
Definition: stateless_allocator.h:38
p
const char * p
Definition: ctype-mb.cc:1235
Stateless_allocator::rebind::other
Stateless_allocator< U, ALLOC_FUN, DEALLOC_FUN > other
Definition: stateless_allocator.h:155
Stateless_allocator::address
pointer address(reference r) const
Definition: stateless_allocator.h:109