fe::Arena Class Reference

An arena pre-allocates so-called pages of size Arena::page_size_. More...

#include <fe/arena.h>

Classes
class	MemoryResource
	A memory resource bridge in order to use this Arena for pmr containers. More...
struct	Allocator
	An allocator in order to use this Arena for containers. More...
struct	Deleter

Public Types
template<class T>
using	Ptr = std::unique_ptr<T, Deleter<T>>
using	State = std::pair<size_t, size_t>

Public Member Functions
Construction
	Arena (const Arena &)=delete
	Arena (size_t page_size=Default_Page_Size)
	Arena (Arena &&other) noexcept
Arena &	operator= (Arena)=delete
template<class T>
constexpr Allocator< T >	allocator () noexcept
	Create Allocator from Arena.
std::pmr::memory_resource *	resource () noexcept
const std::pmr::memory_resource *	resource () const noexcept
template<class T, class... Args>
constexpr Ptr< T >	mk (Args &&... args)
	This is a std::unique_ptr that uses the Arena under the hood and whose Deleter will only invoke the destructor but not delete anything; memory will be released upon destruction of the Arena.
Allocate
constexpr void *	allocate (size_t num_bytes, size_t align)
	Get n bytes of fresh memory.
template<class T>
constexpr T *	allocate (size_t num_elems)
Deallocate
Deallocate memory again in reverse order. Use like this: auto state = arena.state(); auto ptr = arena.allocate(n); if (/* I don't want that */) arena.deallocate(state); Warning Only use, if you really know what you are doing.
constexpr void	deallocate (size_t num_bytes) noexcept
	Removes num_bytes again.
State	state () const noexcept
void	deallocate (State state) noexcept

Static Public Member Functions
static constexpr size_t	align (size_t i, size_t a) noexcept
	Align i to a.

Static Public Attributes
static constexpr size_t	Default_Page_Size = 1024 * 1024
	1MB.

Friends
void	swap (Arena &a1, Arena &a2) noexcept

Detailed Description

An arena pre-allocates so-called pages of size Arena::page_size_.

You can use Arena::allocate to obtain memory from this. When a page runs out of memory, the next page will be (pre-)allocated. You cannot directly release memory obtained via this method. Instead, all memory acquired via this Arena will be released as soon as this Arena will be destroyed. As an exception, you can Arena::deallocate memory that has just been acquired.

Definition at line 21 of file arena.h.

Member Typedef Documentation

Ptr

template<class T>

using fe::Arena::Ptr = std::unique_ptr<T, Deleter<T>>

Definition at line 85 of file arena.h.

State

using fe::Arena::State = std::pair<size_t, size_t>

Definition at line 86 of file arena.h.

Constructor & Destructor Documentation

Arena() [1/3]

fe::Arena::Arena ( const Arena & )

delete

References Arena().

Referenced by fe::Arena::Allocator< T >::Allocator(), Arena(), Arena(), fe::Arena::MemoryResource::MemoryResource(), operator=(), and swap.

Arena() [2/3]

fe::Arena::Arena ( size_t page_size = Default_Page_Size )

inlineexplicit

Definition at line 91 of file arena.h.

References Default_Page_Size.

Arena() [3/3]

fe::Arena::Arena ( Arena && other )

inlinenoexcept

Definition at line 95 of file arena.h.

References Arena(), and swap.

Member Function Documentation

align()

constexpr size_t fe::Arena::align ( size_t i, size_t a )

inlinestaticconstexprnoexcept

Align i to a.

Definition at line 194 of file arena.h.

Referenced by allocate().

allocate() [1/2]

void * fe::Arena::allocate ( size_t num_bytes, size_t align )

inlinenodiscardconstexpr

Get n bytes of fresh memory.

Note

When a fresh page is allocated, its base is only aligned to the align of the allocation that triggered it. A later allocation in the same page that requests a larger alignment has its offset aligned but may still be under-aligned relative to its request. This is a non-issue for the default (max-aligned) page size and for arenas with uniform alignment; only tiny custom arenas mixing alignments can hit it.

Definition at line 135 of file arena.h.

References align().

Referenced by allocate(), and mk().

allocate() [2/2]

template<class T>

T * fe::Arena::allocate ( size_t num_elems )

inlinenodiscardconstexpr

Definition at line 151 of file arena.h.

References allocate().

allocator()

template<class T>

Allocator< T > fe::Arena::allocator ( )

inlineconstexprnoexcept

Create Allocator from Arena.

Definition at line 103 of file arena.h.

Referenced by fe::Arena::Allocator< T >::Allocator().

deallocate() [1/2]

void fe::Arena::deallocate ( size_t num_bytes )

inlineconstexprnoexcept

Removes num_bytes again.

Definition at line 168 of file arena.h.

deallocate() [2/2]

void fe::Arena::deallocate ( State state )

inlinenoexcept

Definition at line 174 of file arena.h.

References state().

mk()

template<class T, class... Args>

Ptr< T > fe::Arena::mk ( Args &&... args )

inlineconstexpr

This is a std::unique_ptr that uses the Arena under the hood and whose Deleter will only invoke the destructor but not delete anything; memory will be released upon destruction of the Arena.

Use like this:

auto ptr = arena.mk<Foo>(a, b, c); // new Foo(a, b, c) placed into arena

Definition at line 120 of file arena.h.

References allocate().

operator=()

Arena & fe::Arena::operator= ( Arena )

delete

References Arena().

resource() [1/2]

const std::pmr::memory_resource * fe::Arena::resource ( ) const

inlinenoexcept

Definition at line 108 of file arena.h.

resource() [2/2]

std::pmr::memory_resource * fe::Arena::resource ( )

inlinenoexcept

Definition at line 107 of file arena.h.

Referenced by fe::Arena::MemoryResource::do_is_equal().

state()

State fe::Arena::state ( ) const

inlinenodiscardnoexcept

Definition at line 172 of file arena.h.

Referenced by deallocate().

Friends And Related Symbol Documentation

swap

void swap ( Arena & a1, Arena & a2 )

friend

Definition at line 184 of file arena.h.

References Arena(), and swap.

Referenced by Arena(), and swap.

Member Data Documentation

Default_Page_Size

size_t fe::Arena::Default_Page_Size = 1024 * 1024

staticconstexpr

1MB.

Definition at line 23 of file arena.h.

Referenced by Arena().

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

• fe/arena.h