FreeList

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.

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.

struct FreeList (

ParentAllocator

size_t minSize

size_t maxSize = minSize

Flag!"adaptive" adaptive = No.adaptive

) {

string text(T args) via import std.conv : text;;

T enforce(T value, Throwable ex) via import std.exception : enforce;;

eponymoustemplate hasMember(T, string name) via import std.traits : hasMember;;

struct Ternary via import std.typecons : Ternary;;

struct NullAllocator via import std.experimental.allocator.building_blocks.null_allocator : NullAllocator;;

static if(minSize == chooseAtRuntime)

size_t min [@property getter];

static if(minSize == chooseAtRuntime)

size_t min [@property setter];

static if(maxSize == chooseAtRuntime)

size_t max [@property getter];

static if(maxSize == chooseAtRuntime)

size_t max [@property setter];

static if(stateSize!ParentAllocator)

ParentAllocator parent;

alias alignment = ParentAllocator.alignment;

size_t goodAllocSize(size_t bytes);

void[] allocate(size_t n);

bool deallocate(void[] block);

static if(hasMember!(ParentAllocator, "deallocateAll"))

bool deallocateAll();

static if(hasMember!(ParentAllocator, "deallocate") && !unchecked)

void minimize();

~this();

}

Destructor

~this ~this(): If ParentAllocator defines deallocate, the list frees all nodes on destruction. FreeList!(0, unbounded) does not deallocate the memory on destruction.

Members

Aliases

alignment alias alignment = ParentAllocator.alignment: Alignment offered.

Functions

allocate void[] allocate(size_t n): 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 bool deallocate(void[] block): 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 bool deallocateAll(): Defined only if ParentAllocator defines deallocateAll. If so, forwards to it and resets the freelist.
goodAllocSize size_t goodAllocSize(size_t bytes): If maxSize == unbounded, returns parent.goodAllocSize(bytes). Otherwise, returns max for sizes in the interval [min, max], and parent.goodAllocSize(bytes) otherwise.
minimize void 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.

Properties

max size_t max [@property getter]: 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 size_t max [@property setter]: If FreeList has been instantiated with maxSize == chooseAtRuntime, then the max property is writable. Setting it must precede any allocation.
min size_t min [@property getter]: Returns the smallest allocation size eligible for allocation from the freelist. (If minSize != chooseAtRuntime, this is simply an alias for minSize.)
min size_t min [@property setter]: If FreeList has been instantiated with minSize == chooseAtRuntime, then the min property is writable. Setting it must precede any allocation.

Variables

parent ParentAllocator parent;: The parent allocator. Depending on whether ParentAllocator holds state or not, this is a member variable or an alias for ParentAllocator.instance.