memory_pool< PoolType, BlockOrRawAllocator > Class Template Reference

Detailed Description

template<typename PoolType = node_pool, class BlockOrRawAllocator = default_allocator>
class foonathan::memory::memory_pool< PoolType, BlockOrRawAllocator >

A stateful RawAllocator that manages nodes of fixed size.

It uses a memory_arena with a given BlockOrRawAllocator defaulting to growing_block_allocator, subdivides them in small nodes of given size and puts them onto a free list. Allocation and deallocation simply remove or add nodes from this list and are thus fast. The way the list is maintained can be controlled via the PoolType which is either node_pool, array_pool or small_node_pool.
This kind of allocator is ideal for fixed size allocations and deallocations in any order, for example in a node based container like std::list. It is not so good for different allocation sizes and has some drawbacks for arrays as described in memory_pool_type.hpp.

Typedefs
using	allocator_type = make_block_allocator_t< BlockOrRawAllocator >
using	pool_type = PoolType

Constants
static constexpr std::size_t	min_node_size

Static Functions
static constexpr std::size_t	min_block_size (std::size_t node_size, std::size_t number_of_nodes) noexcept

Member Functions
template<typename... Args>
	memory_pool (std::size_t node_size, std::size_t block_size, Args &&... args)
	~memory_pool () noexcept
void *	allocate_node ()
void *	try_allocate_node () noexcept
void *	allocate_array (std::size_t n)
void *	try_allocate_array (std::size_t n) noexcept
void	deallocate_node (void *ptr) noexcept
bool	try_deallocate_node (void *ptr) noexcept
void	deallocate_array (void *ptr, std::size_t n) noexcept
bool	try_deallocate_array (void *ptr, std::size_t n) noexcept
std::size_t	node_size () const noexcept
std::size_t	capacity_left () const noexcept
std::size_t	next_capacity () const noexcept
allocator_type &	get_allocator () noexcept
	memory_pool (memory_pool &&other) noexcept
memory_pool &	operator= (memory_pool &&other) noexcept

Constructors

memory_pool() [1/2]

memory_pool	(	std::size_t	node_size,
		std::size_t	block_size,
		Args &&...	args
	)

Effects:

Creates it by specifying the size each node will have, the initial block size for the arena and other constructor arguments for the BlockAllocator. If the node_size is less than the min_node_size, the min_node_size will be the actual node size. It will allocate an initial memory block with given size from the BlockAllocator and puts it onto the free list.

Requires:

node_size must be a valid node size and block_size must be at least min_block_size(node_size, 1).

~memory_pool()

~memory_pool ( )

noexcept

Effects:

Destroys the memory_pool by returning all memory blocks, regardless of properly deallocated back to the BlockAllocator.

memory_pool() [2/2]

memory_pool ( memory_pool< PoolType, BlockOrRawAllocator > &&  other )

noexcept

Effects:

Moving a memory_pool object transfers ownership over the free list, i.e. the moved from pool is completely empty and the new one has all its memory. That means that it is not allowed to call deallocate_node() on a moved-from allocator even when passing it memory that was previously allocated by this object.

Member Functions

min_block_size()

static constexpr std::size_t min_block_size ( std::size_t  node_size, std::size_t  number_of_nodes  )

staticconstexprnoexcept

Returns:

The minimum block size required for certain number of node.

Requires:

node_size must be a valid node size and number_of_nodes must be a non-zero value.

Note

MSVC's implementation of std::list for example is never empty and always allocates proxy nodes. To get enough memory for N elements of a list, number_of_nodes needs to include the proxy count in addition to N.

operator=()

memory_pool & operator= ( memory_pool< PoolType, BlockOrRawAllocator > &&  other )

noexcept

Effects:

Moving a memory_pool object transfers ownership over the free list, i.e. the moved from pool is completely empty and the new one has all its memory. That means that it is not allowed to call deallocate_node() on a moved-from allocator even when passing it memory that was previously allocated by this object.

allocate_node()

void * allocate_node

(

)

Effects:

Allocates a single node by removing it from the free list. If the free list is empty, a new memory block will be allocated from the arena and put onto it. The new block size will be next_capacity() big.

Returns:

A node of size node_size() suitable aligned, i.e. suitable for any type where sizeof(T) < node_size().

Throws:

Anything thrown by the used BlockAllocator's allocation function if a growth is needed.

try_allocate_node()

void * try_allocate_node ( )

noexcept

Effects:

Allocates a single node similar to allocate_node(). But if the free list is empty, a new block will not be allocated.

Returns:

A suitable aligned node of size node_size() or nullptr.

allocate_array()

void * allocate_array

(

std::size_t

n

)

Effects:

Allocates an array of nodes by searching for n continuous nodes on the list and removing them. Depending on the PoolType this can be a slow operation or not allowed at all. This can sometimes lead to a growth, even if technically there is enough continuous memory on the free list.

Returns:

An array of n nodes of size node_size() suitable aligned.

Throws:

Anything thrown by the used BlockAllocator's allocation function if a growth is needed, or bad_array_size if n * node_size() is too big.

Requires:

n must be valid array count.

try_allocate_array()

void * try_allocate_array ( std::size_t  n )

noexcept

Effects:

Allocates an array of nodes similar to allocate_array(). But it will never allocate a new memory block.

Returns:

An array of n nodes of size node_size() suitable aligned or nullptr.

deallocate_node()

void deallocate_node ( void *  ptr )

noexcept

Effects:

Deallocates a single node by putting it back onto the free list.

Requires:

ptr must be a result from a previous call to allocate_node() on the same free list, i.e. either this allocator object or a new object created by moving this to it.

try_deallocate_node()

bool try_deallocate_node ( void *  ptr )

noexcept

Effects:

Deallocates a single node but it does not be a result of a previous call to allocate_node().

Returns:

true if the node could be deallocated, false otherwise.

Note

Some free list implementations can deallocate any memory, doesn't matter where it is coming from.

deallocate_array()

void deallocate_array ( void *  ptr, std::size_t  n  )

noexcept

Effects:

Deallocates an array by putting it back onto the free list.

Requires:

ptr must be a result from a previous call to allocate_array() with the same n on the same free list, i.e. either this allocator object or a new object created by moving this to it.

try_deallocate_array()

bool try_deallocate_array ( void *  ptr, std::size_t  n  )

noexcept

Effects:

Deallocates an array but it does not be a result of a previous call to allocate_array().

Returns:

true if the node could be deallocated, false otherwise.

Note

Some free list implementations can deallocate any memory, doesn't matter where it is coming from.

node_size()

std::size_t node_size ( ) const

noexcept

Returns:

The size of each node in the pool, this is either the same value as in the constructor or min_node_size if the value was too small.

capacity_left()

std::size_t capacity_left ( ) const

noexcept

Effects:

Returns the total amount of bytes remaining on the free list. Divide it by node_size() to get the number of nodes that can be allocated without growing the arena.

Note

Array allocations may lead to a growth even if the capacity_left left is big enough.

next_capacity()

std::size_t next_capacity ( ) const

noexcept

Returns:

The size of the next memory block after the free list gets empty and the arena grows. capacity_left() will increase by this amount.

Note

Due to fence memory in debug mode this cannot be just divided by the node_size() to get the number of nodes.

get_allocator()

allocator_type & get_allocator ( )

noexcept

Returns:

A reference to the BlockAllocator used for managing the arena.

Requires:

It is undefined behavior to move this allocator out into another object.