Free list allocator, stackable on top of
another allocator. Allocation requests between min and max bytes are
rounded up to max and served from a singly-linked list of buffers
deallocated in the past. All other allocations are directed to ParentAllocator. Due to the simplicity of free list management, allocations
from the free list are fast. If adaptive is set to Yes.adaptive,
the free list gradually reduces its size if allocations tend to use the parent
allocator much more than the lists' available nodes.
struct FreeList(ParentAllocator,
ulong minSize,
ulong maxSize
= minSize,
Flag!("adaptive") adaptive
= No.adaptive)
;
One instantiation is of particular interest: FreeList!(0, unbounded) puts
every deallocation in the freelist, and subsequently serves any allocation from
the freelist (if not empty). There is no checking of size matching, which would
be incorrect for a freestanding allocator but is both correct and fast when an
owning allocator on top of the free list allocator (such as Segregator) is
already in charge of handling size checking.
The following methods are defined if ParentAllocator defines them, and
forward to it: expand, owns, reallocate.
Fields
| Name | Type | Description |
parent
|
ParentAllocator | The parent allocator. Depending on whether ParentAllocator holds state
or not, this is a member variable or an alias for
ParentAllocator.instance.
|
Properties
| Name | Type | Description |
max[get]
|
size_t | Returns the largest allocation size eligible for allocation from the
freelist. (If maxSize != chooseAtRuntime, this is simply an alias
for maxSize.) All allocation requests for sizes greater than or
equal to min and less than or equal to max are rounded to max and forwarded to the parent allocator. When the block fitting the
same constraint gets deallocated, it is put in the freelist with the
allocated size assumed to be max.
|
max[set]
|
size_t | If FreeList has been instantiated with maxSize ==
chooseAtRuntime, then the max property is writable. Setting it
must precede any allocation.
|
min[get]
|
size_t | Returns the smallest allocation size eligible for allocation from the
freelist. (If minSize != chooseAtRuntime, this is simply an alias
for minSize.)
|
min[set]
|
size_t | If FreeList has been instantiated with minSize ==
chooseAtRuntime, then the min property is writable. Setting it
must precede any allocation.
|
Methods
| Name | Description |
allocate
|
Allocates memory either off of the free list or from the parent allocator.
If n is within [min, max] or if the free list is unchecked
(minSize == 0 && maxSize == size_t.max), then the free list is
consulted first. If not empty (hit), the block at the front of the free
list is removed from the list and returned. Otherwise (miss), a new block
of max bytes is allocated, truncated to n bytes, and returned.
|
deallocate
|
If block.length is within [min, max] or if the free list is
unchecked (minSize == 0 && maxSize == size_t.max), then inserts the
block at the front of the free list. For all others, forwards to parent.deallocate if Parent.deallocate is defined.
|
deallocateAll
|
Defined only if ParentAllocator defines deallocateAll. If so,
forwards to it and resets the freelist.
|
goodAllocSize
|
If maxSize == unbounded, returns parent.goodAllocSize(bytes).
Otherwise, returns max for sizes in the interval [min, max], and
parent.goodAllocSize(bytes) otherwise.
|
minimize
|
Nonstandard function that minimizes the memory usage of the freelist by
freeing each element in turn. Defined only if ParentAllocator defines
deallocate. FreeList!(0, unbounded) does not have this function.
|
