Documentation of memory

( foonathan/memory)

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
 

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 * allocate_array (std::size_t n)
 
void deallocate_node (void *ptr) noexcept
 
void 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_pooloperator= (memory_pool &&other) noexcept
 

Constructors

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 a non-zero value.
~memory_pool ( )
noexcept
Effects:
Destroys the memory_pool by returning all memory blocks, regardless of properly deallocated back to the BlockAllocator.
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

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.
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.
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.
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.
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.
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.
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.
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. This function just forwards to the memory_arena.
Note
Due to fence memory, alignment buffers and the like this may not be the exact result capacity_left() will return, but it is an upper bound to it.
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.