pool_allocator.h
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// Allocators -*- C++ -*-
// Copyright (C) 2001-2024 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library 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; either version 3, or (at your option)
// any later version.
// This library 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.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/*
* Copyright (c) 1996-1997
* Silicon Graphics Computer Systems, Inc.
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Silicon Graphics makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*/
/** @file ext/pool_allocator.h
* This file is a GNU extension to the Standard C++ Library.
*/
#ifndef _POOL_ALLOCATOR_H
#define _POOL_ALLOCATOR_H 1
#include <bits/requires_hosted.h> // GNU extensions are currently omitted
#include <bits/c++config.h>
#include <cstdlib>
#include <new>
#include <bits/functexcept.h>
#include <ext/atomicity.h>
#include <ext/concurrence.h>
#include <bits/move.h>
#if __cplusplus >= 201103L
#include <type_traits>
#endif
namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @brief Base class for __pool_alloc.
*
* Uses various allocators to fulfill underlying requests (and makes as
* few requests as possible when in default high-speed pool mode).
*
* Important implementation properties:
* 0. If globally mandated, then allocate objects from new
* 1. If the clients request an object of size > _S_max_bytes, the resulting
* object will be obtained directly from new
* 2. In all other cases, we allocate an object of size exactly
* _S_round_up(requested_size). Thus the client has enough size
* information that we can return the object to the proper free list
* without permanently losing part of the object.
*/
class __pool_alloc_base
{
typedef std::size_t size_t;
protected:
enum { _S_align = 8 };
enum { _S_max_bytes = 128 };
enum { _S_free_list_size = (size_t)_S_max_bytes / (size_t)_S_align };
union _Obj
{
union _Obj* _M_free_list_link;
char _M_client_data[1]; // The client sees this.
};
static _Obj* volatile _S_free_list[_S_free_list_size];
// Chunk allocation state.
static char* _S_start_free;
static char* _S_end_free;
static size_t _S_heap_size;
size_t
_M_round_up(size_t __bytes)
{ return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
_GLIBCXX_CONST _Obj* volatile*
_M_get_free_list(size_t __bytes) throw ();
__mutex&
_M_get_mutex() throw ();
// Returns an object of size __n, and optionally adds to size __n
// free list.
void*
_M_refill(size_t __n);
// Allocates a chunk for nobjs of size size. nobjs may be reduced
// if it is inconvenient to allocate the requested number.
char*
_M_allocate_chunk(size_t __n, int& __nobjs);
};
/**
* @brief Allocator using a memory pool with a single lock.
* @ingroup allocators
*/
template<typename _Tp>
class __pool_alloc : private __pool_alloc_base
{
private:
static _Atomic_word _S_force_new;
public:
typedef std::size_t size_type;
typedef std::ptrdiff_t difference_type;
typedef _Tp* pointer;
typedef const _Tp* const_pointer;
typedef _Tp& reference;
typedef const _Tp& const_reference;
typedef _Tp value_type;
template<typename _Tp1>
struct rebind
{ typedef __pool_alloc<_Tp1> other; };
#if __cplusplus >= 201103L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2103. propagate_on_container_move_assignment
typedef std::true_type propagate_on_container_move_assignment;
#endif
__pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
__pool_alloc(const __pool_alloc&) _GLIBCXX_USE_NOEXCEPT { }
template<typename _Tp1>
__pool_alloc(const __pool_alloc<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
~__pool_alloc() _GLIBCXX_USE_NOEXCEPT { }
pointer
address(reference __x) const _GLIBCXX_NOEXCEPT
{ return std::__addressof(__x); }
const_pointer
address(const_reference __x) const _GLIBCXX_NOEXCEPT
{ return std::__addressof(__x); }
size_type
max_size() const _GLIBCXX_USE_NOEXCEPT
{ return std::size_t(-1) / sizeof(_Tp); }
#if __cplusplus >= 201103L
template<typename _Up, typename... _Args>
void
construct(_Up* __p, _Args&&... __args)
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
template<typename _Up>
void
destroy(_Up* __p) { __p->~_Up(); }
#else
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 402. wrong new expression in [some_] allocator::construct
void
construct(pointer __p, const _Tp& __val)
{ ::new((void *)__p) _Tp(__val); }
void
destroy(pointer __p) { __p->~_Tp(); }
#endif
_GLIBCXX_NODISCARD pointer
allocate(size_type __n, const void* = 0);
void
deallocate(pointer __p, size_type __n);
};
template<typename _Tp>
inline bool
operator==(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
{ return true; }
#if __cpp_impl_three_way_comparison < 201907L
template<typename _Tp>
inline bool
operator!=(const __pool_alloc<_Tp>&, const __pool_alloc<_Tp>&)
{ return false; }
#endif
template<typename _Tp>
_Atomic_word
__pool_alloc<_Tp>::_S_force_new;
template<typename _Tp>
_GLIBCXX_NODISCARD _Tp*
__pool_alloc<_Tp>::allocate(size_type __n, const void*)
{
using std::size_t;
pointer __ret = 0;
if (__builtin_expect(__n != 0, true))
{
if (__n > this->max_size())
std::__throw_bad_alloc();
const size_t __bytes = __n * sizeof(_Tp);
#if __cpp_aligned_new
if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
{
std::align_val_t __al = std::align_val_t(alignof(_Tp));
return static_cast<_Tp*>(::operator new(__bytes, __al));
}
#endif
// If there is a race through here, assume answer from getenv
// will resolve in same direction. Inspired by techniques
// to efficiently support threading found in basic_string.h.
if (_S_force_new == 0)
{
if (std::getenv("GLIBCXX_FORCE_NEW"))
__atomic_add_dispatch(&_S_force_new, 1);
else
__atomic_add_dispatch(&_S_force_new, -1);
}
if (__bytes > size_t(_S_max_bytes) || _S_force_new > 0)
__ret = static_cast<_Tp*>(::operator new(__bytes));
else
{
_Obj* volatile* __free_list = _M_get_free_list(__bytes);
__scoped_lock sentry(_M_get_mutex());
_Obj* __restrict__ __result = *__free_list;
if (__builtin_expect(__result == 0, 0))
__ret = static_cast<_Tp*>(_M_refill(_M_round_up(__bytes)));
else
{
*__free_list = __result->_M_free_list_link;
__ret = reinterpret_cast<_Tp*>(__result);
}
if (__ret == 0)
std::__throw_bad_alloc();
}
}
return __ret;
}
template<typename _Tp>
void
__pool_alloc<_Tp>::deallocate(pointer __p, size_type __n)
{
using std::size_t;
if (__builtin_expect(__n != 0 && __p != 0, true))
{
#if __cpp_aligned_new
if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
{
::operator delete(__p, std::align_val_t(alignof(_Tp)));
return;
}
#endif
const size_t __bytes = __n * sizeof(_Tp);
if (__bytes > static_cast<size_t>(_S_max_bytes) || _S_force_new > 0)
::operator delete(__p);
else
{
_Obj* volatile* __free_list = _M_get_free_list(__bytes);
_Obj* __q = reinterpret_cast<_Obj*>(__p);
__scoped_lock sentry(_M_get_mutex());
__q ->_M_free_list_link = *__free_list;
*__free_list = __q;
}
}
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif
new
type_traits
requires_hosted.h
move.h
functexcept.h
c++config.h
concurrence.h
atomicity.h
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:111
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:51
__gnu_cxx
GNU extensions for public use.
std::auto_ptr_ref
Definition auto_ptr.h:49
__gnu_cxx::__pool_alloc_base
Base class for __pool_alloc.
Definition pool_allocator.h:78
__gnu_cxx::__pool_alloc
Allocator using a memory pool with a single lock.
Definition pool_allocator.h:127
cstdlib