llfio_v2_xxx::mapped< T > Class Template Reference

Provides an owning, typed view of memory mapped from a section_handle or a file_handle suitable for feeding to STL algorithms or the Ranges TS. More...

#include "mapped.hpp"

Inheritance diagram for llfio_v2_xxx::mapped< T >:

Public Types
using	extent_type = typename section_handle::extent_type
	The extent type.
using	size_type = typename section_handle::size_type
	The size type.
using	element_type = typename span< T >::element_type
	The index type. More...
using	value_type = typename span< T >::value_type
	The value type.
using	reference = typename span< T >::reference
	The reference type.
using	pointer = typename span< T >::pointer
	The pointer type.
using	const_reference = typename span< T >::const_reference
	The const reference type.
using	const_pointer = typename span< T >::const_pointer
	The const pointer type.
using	iterator = typename span< T >::iterator
	The iterator type.
using	reverse_iterator = typename span< T >::reverse_iterator
	The const iterator type. More...
using	difference_type = typename span< T >::difference_type
	The const reverse iterator type. More...

Public Member Functions
constexpr	mapped ()
	Default constructor.
	mapped (const mapped &)=delete
	mapped (mapped &&o) noexcept
mapped &	operator= (const mapped &)=delete
mapped &	operator= (mapped &&o) noexcept
	~mapped ()
	Detaches the array of T, before tearing down the map.
const section_handle &	section () const noexcept
	Returns a reference to the internal section handle.
const map_handle &	map () const noexcept
	Returns a reference to the internal map handle.
span< T >	as_span () const noexcept
	Returns a span referring to this mapped region.
	mapped (size_type length, bool zeroed=false, section_handle::flag _flag=section_handle::flag::readwrite)
	mapped (section_handle &sh, size_type length=(size_type) -1, extent_type byteoffset=0, section_handle::flag _flag=section_handle::flag::readwrite)
	mapped (file_handle &backing, size_type length=(size_type) -1, extent_type maximum_size=0, extent_type byteoffset=0, section_handle::flag _flag=section_handle::flag::readwrite)

Detailed Description

template<class T>
class llfio_v2_xxx::mapped< T >

Provides an owning, typed view of memory mapped from a section_handle or a file_handle suitable for feeding to STL algorithms or the Ranges TS.

This opens a new map_handle (and if necessary a section_handle) onto the requested offset and length of the supplied source, and thus is an owning view of mapped memory. It can be moved, but not copied.

The array of objects upon which the owning view is opened is attached via in_place_detach<T>() in the mapped constructor. In the final destructor (i.e. not the destructor of any moved-from instances), the array of objects is detached via in_place_detach<T>() just before the map_handle is destroyed. As it is illegal to attach objects into more than one address or process at a time, you must not call mapped on objects already mapped into any process anywhere else.

These owning semantics are convenient, but may be too heavy for your use case. You can gain more fine grained control using map_handle/mapped_file_handle directly with P1631 attached<T>.

Note

Only on the clang compiler, does mapped actually use P1631 in_place_attach/in_place_detach, as currently GCC and MSVC do two memcpy's of the mapped region. Also, we restrict the use of in_place_attach/in_place_detach to regions less than 4Kb in size, as even clang falls down on large regions.

Optionally can issue a blocking write barrier on destruction of the mapped view by setting the flag section_handle::flag::barrier_on_close, thus forcing any changes to data referred to by this to storage before the destructor returns.

Member Typedef Documentation

difference_type

template<class T >

using llfio_v2_xxx::mapped< T >::difference_type = typename span<T>::difference_type

The const reverse iterator type.

The difference type

element_type

template<class T >

using llfio_v2_xxx::mapped< T >::element_type = typename span<T>::element_type

The index type.

The element type

reverse_iterator

template<class T >

using llfio_v2_xxx::mapped< T >::reverse_iterator = typename span<T>::reverse_iterator

The const iterator type.

The reverse iterator type

Constructor & Destructor Documentation

mapped() [1/3]

template<class T >

llfio_v2_xxx::mapped< T >::mapped ( size_type  length, bool  zeroed = false, section_handle::flag  _flag = section_handle::flag::readwrite  )

inlineexplicit

Create a view of newly allocated unused memory, creating new memory if insufficient unused memory is available. Note that the memory mapped by this call may contain non-zero bits (recycled memory) unless zeroed is true.

Parameters

length	The number of items to map.
zeroed	Whether to ensure that the viewed memory returned is all bits zero or not.
_flag	The flags to pass to map_handle::map().

      : _maph(map_handle::map(length * sizeof(T), zeroed, _flag).value())
  {
    byte *addr = _maph.address();
    static_cast<span<T> &>(*this) = detail::attach_or_reinterpret<T>::attach({addr, length * sizeof(T)});
  }

mapped() [2/3]

template<class T >

llfio_v2_xxx::mapped< T >::mapped ( section_handle &  sh, size_type  length = (size_type) -1, extent_type  byteoffset = 0, section_handle::flag  _flag = section_handle::flag::readwrite  )

inlineexplicit

Construct a mapped view of the given section handle.

Parameters

sh	The section handle to use as the data source for creating the map.
length	The number of items to map, use -1 to mean the length of the section handle divided by sizeof(T).
byteoffset	The byte offset into the section handle, this does not need to be a multiple of the page size.
_flag	The flags to pass to map_handle::map().

      : mapped((length == 0) ? mapped() :
                               mapped(nullptr, 0,
#ifdef _WIN32
                                      byteoffset & ~65535,
#else
                                      utils::round_down_to_page_size(byteoffset, utils::page_size()),
#endif
                                      byteoffset, &sh, (length == (size_type) -1) ? 0 : length * sizeof(T), _flag))  // NOLINT
  {
  }

mapped() [3/3]

template<class T >

llfio_v2_xxx::mapped< T >::mapped ( file_handle &  backing, size_type  length = (size_type) -1, extent_type  maximum_size = 0, extent_type  byteoffset = 0, section_handle::flag  _flag = section_handle::flag::readwrite  )

inlineexplicit

Construct a mapped view of the given file.

Parameters

backing	The handle to use as backing storage.
length	The number of items to map, use -1 to mean the length of the section handle divided by sizeof(T).
maximum_size	The initial size of this section in bytes, which cannot be larger than any backing file. Zero means to use backing.maximum_extent().
byteoffset	The byte offset into the section handle, this does not need to be a multiple of the page size.
_flag	The flags to pass to map_handle::map().

      : mapped((length == 0) ? mapped() :
                               mapped(&backing, maximum_size,
#ifdef _WIN32
                                      byteoffset & ~65535,
#else
                                      utils::round_down_to_page_size(byteoffset, utils::page_size()),
#endif
                                      byteoffset, nullptr, (length == (size_type) -1) ? 0 : length * sizeof(T), _flag))  // NOLINT
  {
  }

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The documentation for this class was generated from the following file:

• include/llfio/v2.0/mapped.hpp