1 /* Copyright (c) 2014, 2021, Oracle and/or its affiliates.
2 
3    This program is free software; you can redistribute it and/or modify
4    it under the terms of the GNU General Public License, version 2.0,
5    as published by the Free Software Foundation.
6 
7    This program is also distributed with certain software (including
8    but not limited to OpenSSL) that is licensed under separate terms,
9    as designated in a particular file or component or in included license
10    documentation.  The authors of MySQL hereby grant you an additional
11    permission to link the program and your derivative works with the
12    separately licensed software that they have included with MySQL.
13 
14    This program is distributed in the hope that it will be useful,
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.
18 
19    You should have received a copy of the GNU General Public License
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 MEMROOT_ALLOCATOR_INCLUDED
24 #define MEMROOT_ALLOCATOR_INCLUDED
25 
26 #include "sql_alloc.h"
27 
28 #include <new>
29 #include <limits>
30 
31 
32 /**
33   Memroot_allocator is a C++ STL memory allocator based on MEM_ROOT.
34 
35   No deallocation is done by this allocator. Calling init_sql_alloc()
36   and free_root() on the supplied MEM_ROOT is the responsibility of
37   the caller. Do *not* call free_root() until the destructor of any
38   objects using this allocator has completed. This includes iterators.
39 
40   Example of use:
41   vector<int, Memroot_allocator<int> > v((Memroot_allocator<int>(&mem_root)));
42 
43   @note allocate() throws std::bad_alloc() similarly to the default
44   STL memory allocator. This is necessary - STL functions which allocates
45   memory expects it. Otherwise these functions will try to use the memory,
46   leading to seg faults if memory allocation was not successful.
47 
48   @note This allocator cannot be used for std::basic_string
49   because of this libstd++ bug:
50   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56437
51   "basic_string assumes that allocators are default-constructible"
52 
53   @note C++98 says that STL implementors can assume that allocator objects
54   of the same type always compare equal. This will only be the case for
55   two Memroot_allocators that use the same MEM_ROOT. Care should be taken
56   when this is not the case. Especially:
57   - Using list::splice() on two lists with allocators using two different
58     MEM_ROOTs causes undefined behavior. Most implementations seem to give
59     runtime errors in such cases.
60   - swap() on two collections with allocators using two different MEM_ROOTs
61     is not well defined. At least some implementations also swap allocators,
62     but this should not be depended on.
63 */
64 
65 template <class T> class Memroot_allocator
66 {
67   // This cannot be const if we want to be able to swap.
68   MEM_ROOT *m_memroot;
69 
70 public:
71   typedef T value_type;
72   typedef size_t size_type;
73   typedef ptrdiff_t difference_type;
74 
75   typedef T* pointer;
76   typedef const T* const_pointer;
77 
78   typedef T& reference;
79   typedef const T& const_reference;
80 
address(reference r)81   pointer address(reference r) const { return &r; }
address(const_reference r)82   const_pointer address(const_reference r) const { return &r; }
83 
Memroot_allocator(MEM_ROOT * memroot)84   explicit Memroot_allocator(MEM_ROOT *memroot) : m_memroot(memroot)
85   {}
86 
Memroot_allocator(const Memroot_allocator<U> & other)87   template <class U> Memroot_allocator(const Memroot_allocator<U> &other)
88     : m_memroot(other.memroot())
89   {}
90 
91   template <class U> Memroot_allocator & operator=
92     (const Memroot_allocator<U> &other)
93   {
94     assert(m_memroot == other.memroot()); // Don't swap memroot.
95   }
96 
~Memroot_allocator()97   ~Memroot_allocator()
98   {}
99 
100   pointer allocate(size_type n, const_pointer hint= 0)
101   {
102     if (n == 0)
103       return NULL;
104     if (n > max_size())
105       throw std::bad_alloc();
106 
107     pointer p= static_cast<pointer>(alloc_root(m_memroot, n * sizeof(T)));
108     if (p == NULL)
109       throw std::bad_alloc();
110     return p;
111   }
112 
deallocate(pointer p,size_type n)113   void deallocate(pointer p, size_type n) { }
114 
construct(pointer p,const T & val)115   void construct(pointer p, const T& val)
116   {
117     assert(p != NULL);
118     try {
119       new(p) T(val);
120     } catch (...) {
121       assert(false); // Constructor should not throw an exception.
122     }
123   }
124 
destroy(pointer p)125   void destroy(pointer p)
126   {
127     assert(p != NULL);
128     try {
129       p->~T();
130     } catch (...) {
131       assert(false); // Destructor should not throw an exception
132     }
133   }
134 
max_size()135   size_type max_size() const
136   {
137     return std::numeric_limits<size_t>::max() / sizeof(T);
138   }
139 
140   template <class U> struct rebind { typedef Memroot_allocator<U> other; };
141 
memroot()142   MEM_ROOT *memroot() const { return m_memroot; }
143 };
144 
145 template <class T>
146 bool operator== (const Memroot_allocator<T>& a1, const Memroot_allocator<T>& a2)
147 {
148   return a1.memroot() == a2.memroot();
149 }
150 
151 template <class T>
152 bool operator!= (const Memroot_allocator<T>& a1, const Memroot_allocator<T>& a2)
153 {
154   return a1.memroot() != a2.memroot();
155 }
156 
157 #endif // MEMROOT_ALLOCATOR_INCLUDED
158