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
.
Returns the smallest allocation size eligible for allocation from the freelist. (If minSize != chooseAtRuntime
, this is simply an alias for minSize
.)
If FreeList
has been instantiated with minSize == chooseAtRuntime
, then the min
property is writable. Setting it must precede any allocation.
size_t low
| new value for min
|
low <= max
, or maxSize == chooseAtRuntime
and max
has not yet been initialized. Also, no allocation has been yet done with this allocator. min == low
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
.
If FreeList
has been instantiated with maxSize == chooseAtRuntime
, then the max
property is writable. Setting it must precede any allocation.
size_t high
| new value for max
|
high >= min
, or minSize == chooseAtRuntime
and min
has not yet been initialized. Also high >= (void*).sizeof
. Also, no allocation has been yet done with this allocator. max == high
The parent allocator. Depending on whether ParentAllocator
holds state or not, this is a member variable or an alias for ParentAllocator.instance
.
Alignment offered.
If maxSize == unbounded
, returns parent.goodAllocSize(bytes)
. Otherwise, returns max
for sizes in the interval [min, max]
, and parent.goodAllocSize(bytes)
otherwise.
min
and/or max
must be initialized appropriately. result >= bytes
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.
size_t n
| number of bytes to allocate |
null
. min
and/or max
must be initialized appropriately. result.length == bytes || result is null
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.
void[] block
| Block to deallocate. |
min
and/or max
must be initialized appropriately. The block must have been allocated with this freelist, and no dynamic changing of min
or max
is allowed to occur between allocation and deallocation.Defined only if ParentAllocator
defines deallocateAll
. If so, forwards to it and resets the freelist.
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.
Free list built on top of exactly one contiguous block of memory. The block is assumed to have been allocated with ParentAllocator
, and is released in ContiguousFreeList
's destructor (unless ParentAllocator
is NullAllocator
).
ContiguousFreeList
has most advantages of FreeList
but fewer disadvantages. It has better cache locality because items are closer to one another. It imposes less fragmentation on its parent allocator.
The disadvantages of ContiguousFreeList
over FreeList
are its pay upfront model (as opposed to FreeList
's pay-as-you-go approach), and a hard limit on the number of nodes in the list. Thus, a large number of long- lived objects may occupy the entire block, making it unavailable for serving allocations from the free list. However, an absolute cap on the free list size may be beneficial.
The options minSize == unbounded
and maxSize == unbounded
are not available for ContiguousFreeList
.
import std.experimental.allocator.building_blocks.allocator_list : AllocatorList; import std.experimental.allocator.gc_allocator : GCAllocator; import std.experimental.allocator.common : unbounded; alias ScalableFreeList = AllocatorList!((n) => ContiguousFreeList!(GCAllocator, 0, unbounded)(4096) );
The parent allocator. Depending on whether ParentAllocator
holds state or not, this is a member variable or an alias for ParentAllocator.instance
.
Alignment offered.
Constructors setting up the memory structured as a free list.
ubyte[] buffer
| Buffer to structure as a free list. If ParentAllocator is not NullAllocator , the buffer is assumed to be allocated by parent and will be freed in the destructor. |
ParentAllocator parent
| Parent allocator. For construction from stateless allocators, use their instance static member. |
size_t bytes
| Bytes (not items) to be allocated for the free list. Memory will be allocated during construction and deallocated in the destructor. |
size_t max
| Maximum size eligible for freelisting. Construction with this parameter is defined only if maxSize == chooseAtRuntime or maxSize == unbounded . |
size_t min
| Minimum size eligible for freelisting. Construction with this parameter is defined only if minSize == chooseAtRuntime . If this condition is met and no min parameter is present, min is initialized with max . |
If n
is eligible for freelisting, returns max
. Otherwise, returns parent.goodAllocSize(n)
.
min
and/or max
must be initialized appropriately. result >= bytes
Allocate n
bytes of memory. If n
is eligible for freelist and the freelist is not empty, pops the memory off the free list. In all other cases, uses the parent allocator.
Defined if ParentAllocator
defines it. Checks whether the block belongs to this allocator.
Deallocates b
. If it's of eligible size, it's put on the free list. Otherwise, it's returned to parent
.
b
has been allocated with this allocator, or is null
.Deallocates everything from the parent.
Returns Ternary.yes
if no memory is currently allocated with this allocator, Ternary.no
otherwise. This method never returns Ternary.unknown
.
FreeList shared across threads. Allocation and deallocation are lock-free. The parameters have the same semantics as for FreeList
.
expand
is defined to forward to ParentAllocator.expand
(it must be also shared
).
import std.experimental.allocator.common : chooseAtRuntime; import std.experimental.allocator.mallocator : Mallocator; shared SharedFreeList!(Mallocator, chooseAtRuntime, chooseAtRuntime) a; a.setBounds(64, 128); writeln(a.max); // 128 writeln(a.min); // 64
import std.experimental.allocator.common : chooseAtRuntime; import std.experimental.allocator.mallocator : Mallocator; shared SharedFreeList!(Mallocator, 50, 50, chooseAtRuntime) a; // Set the maxSize first so setting the minSize doesn't throw a.approxMaxLength = 128; writeln(a.approxMaxLength); // 128 a.approxMaxLength = 1024; writeln(a.approxMaxLength); // 1024 a.approxMaxLength = 1; writeln(a.approxMaxLength); // 1
Properties for getting (and possibly setting) the bounds. Setting bounds is allowed only once , and before any allocation takes place. Otherwise, the primitives have the same semantics as those of FreeList
.
Properties for getting (and possibly setting) the approximate maximum length of a shared freelist.
The parent allocator. Depending on whether ParentAllocator
holds state or not, this is a member variable or an alias for ParentAllocator.instance
.
Standard primitives.
Nonstandard function that minimizes the memory usage of the freelist by freeing each element in turn. Defined only if ParentAllocator
defines deallocate
.
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Licensed under the Boost License 1.0.
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