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Diffstat (limited to 'sql/mem_root_array.h')
| -rw-r--r-- | sql/mem_root_array.h | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/sql/mem_root_array.h b/sql/mem_root_array.h new file mode 100644 index 00000000000..5ce4dcb584d --- /dev/null +++ b/sql/mem_root_array.h @@ -0,0 +1,175 @@ +/* Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; version 2 of the License. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ + + +#ifndef MEM_ROOT_ARRAY_INCLUDED +#define MEM_ROOT_ARRAY_INCLUDED + +#include <my_alloc.h> + +/** + A typesafe replacement for DYNAMIC_ARRAY. + We use MEM_ROOT for allocating storage, rather than the C++ heap. + The interface is chosen to be similar to std::vector. + + @remark + Unlike DYNAMIC_ARRAY, elements are properly copied + (rather than memcpy()d) if the underlying array needs to be expanded. + + @remark + Depending on has_trivial_destructor, we destroy objects which are + removed from the array (including when the array object itself is destroyed). + + @remark + Note that MEM_ROOT has no facility for reusing free space, + so don't use this if multiple re-expansions are likely to happen. + + @param Element_type The type of the elements of the container. + Elements must be copyable. + @param has_trivial_destructor If true, we don't destroy elements. + We could have used type traits to determine this. + __has_trivial_destructor is supported by some (but not all) + compilers we use. +*/ +template<typename Element_type, bool has_trivial_destructor> +class Mem_root_array +{ +public: + Mem_root_array(MEM_ROOT *root) + : m_root(root), m_array(NULL), m_size(0), m_capacity(0) + { + DBUG_ASSERT(m_root != NULL); + } + + ~Mem_root_array() + { + clear(); + } + + Element_type &at(size_t n) + { + DBUG_ASSERT(n < size()); + return m_array[n]; + } + + const Element_type &at(size_t n) const + { + DBUG_ASSERT(n < size()); + return m_array[n]; + } + + // Returns a pointer to the first element in the array. + Element_type *begin() { return &m_array[0]; } + + // Returns a pointer to the past-the-end element in the array. + Element_type *end() { return &m_array[size()]; } + + // Erases all of the elements. + void clear() + { + if (!empty()) + chop(0); + } + + /* + Chops the tail off the array, erasing all tail elements. + @param pos Index of first element to erase. + */ + void chop(const size_t pos) + { + DBUG_ASSERT(pos < m_size); + if (!has_trivial_destructor) + { + for (size_t ix= pos; ix < m_size; ++ix) + { + Element_type *p= &m_array[ix]; + p->~Element_type(); // Destroy discarded element. + } + } + m_size= pos; + } + + /* + Reserves space for array elements. + Copies over existing elements, in case we are re-expanding the array. + + @param n number of elements. + @retval true if out-of-memory, false otherwise. + */ + bool reserve(size_t n) + { + if (n <= m_capacity) + return false; + + void *mem= alloc_root(m_root, n * element_size()); + if (!mem) + return true; + Element_type *array= static_cast<Element_type*>(mem); + + // Copy all the existing elements into the new array. + for (size_t ix= 0; ix < m_size; ++ix) + { + Element_type *new_p= &array[ix]; + Element_type *old_p= &m_array[ix]; + new (new_p) Element_type(*old_p); // Copy into new location. + if (!has_trivial_destructor) + old_p->~Element_type(); // Destroy the old element. + } + + // Forget the old array. + m_array= array; + m_capacity= n; + return false; + } + + /* + Adds a new element at the end of the array, after its current last + element. The content of this new element is initialized to a copy of + the input argument. + + @param element Object to copy. + @retval true if out-of-memory, false otherwise. + */ + bool push_back(const Element_type &element) + { + const size_t min_capacity= 20; + const size_t expansion_factor= 2; + if (0 == m_capacity && reserve(min_capacity)) + return true; + if (m_size == m_capacity && reserve(m_capacity * expansion_factor)) + return true; + Element_type *p= &m_array[m_size++]; + new (p) Element_type(element); + return false; + } + + size_t capacity() const { return m_capacity; } + size_t element_size() const { return sizeof(Element_type); } + bool empty() const { return size() == 0; } + size_t size() const { return m_size; } + +private: + MEM_ROOT *const m_root; + Element_type *m_array; + size_t m_size; + size_t m_capacity; + + // Not (yet) implemented. + Mem_root_array(const Mem_root_array&); + Mem_root_array &operator=(const Mem_root_array&); +}; + + +#endif // MEM_ROOT_ARRAY_INCLUDED |