1 /* Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved. 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 MEM_ROOT_ALLOCATOR_INCLUDED 24 #define MEM_ROOT_ALLOCATOR_INCLUDED 25 26 #include <limits> 27 #include <new> 28 #include <utility> // std::forward 29 30 #include "my_alloc.h" 31 #include "my_dbug.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 init_sql_alloc() 37 and free_root() on the supplied MEM_ROOT is the responsibility of 38 the caller. Do *not* call free_root() until the destructor of any 39 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 66 template <class T> 67 class Mem_root_allocator { 68 // This cannot be const if we want to be able to swap. 69 MEM_ROOT *m_memroot; 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 address(reference r)82 pointer address(reference r) const { return &r; } address(const_reference r)83 const_pointer address(const_reference r) const { return &r; } 84 Mem_root_allocator(MEM_ROOT * memroot)85 explicit Mem_root_allocator(MEM_ROOT *memroot) : m_memroot(memroot) {} 86 Mem_root_allocator()87 explicit Mem_root_allocator() : m_memroot(nullptr) {} 88 89 template <class U> Mem_root_allocator(const Mem_root_allocator<U> & other)90 Mem_root_allocator(const Mem_root_allocator<U> &other) 91 : m_memroot(other.memroot()) {} 92 93 template <class U> 94 Mem_root_allocator &operator=( 95 const Mem_root_allocator<U> &other MY_ATTRIBUTE((unused))) { 96 DBUG_ASSERT(m_memroot == other.memroot()); // Don't swap memroot. 97 } 98 99 pointer allocate(size_type n, 100 const_pointer hint MY_ATTRIBUTE((unused)) = nullptr) { 101 if (n == 0) return nullptr; 102 if (n > max_size()) throw std::bad_alloc(); 103 104 pointer p = static_cast<pointer>(m_memroot->Alloc(n * sizeof(T))); 105 if (p == nullptr) throw std::bad_alloc(); 106 return p; 107 } 108 deallocate(pointer,size_type)109 void deallocate(pointer, size_type) {} 110 111 template <class U, class... Args> construct(U * p,Args &&...args)112 void construct(U *p, Args &&... args) { 113 DBUG_ASSERT(p != nullptr); 114 try { 115 ::new ((void *)p) U(std::forward<Args>(args)...); 116 } catch (...) { 117 DBUG_ASSERT(false); // Constructor should not throw an exception. 118 } 119 } 120 destroy(pointer p)121 void destroy(pointer p) { 122 DBUG_ASSERT(p != nullptr); 123 try { 124 p->~T(); 125 } catch (...) { 126 DBUG_ASSERT(false); // Destructor should not throw an exception 127 } 128 } 129 max_size()130 size_type max_size() const { 131 return std::numeric_limits<size_t>::max() / sizeof(T); 132 } 133 134 template <class U> 135 struct rebind { 136 typedef Mem_root_allocator<U> other; 137 }; 138 memroot()139 MEM_ROOT *memroot() const { return m_memroot; } 140 }; 141 142 template <class T> 143 bool operator==(const Mem_root_allocator<T> &a1, 144 const Mem_root_allocator<T> &a2) { 145 return a1.memroot() == a2.memroot(); 146 } 147 148 template <class T> 149 bool operator!=(const Mem_root_allocator<T> &a1, 150 const Mem_root_allocator<T> &a2) { 151 return a1.memroot() != a2.memroot(); 152 } 153 154 #endif // MEM_ROOT_ALLOCATOR_INCLUDED 155