A Region
allocator allocates memory straight from one contiguous chunk. There is no deallocation, and once the region is full, allocation requests return null
. Therefore, Region
s are often used (a) in conjunction with more sophisticated allocators; or (b) for batch-style very fast allocations that deallocate everything at once.
The region only stores three pointers, corresponding to the current position in the store and the limits. One allocation entails rounding up the allocation size for alignment purposes, bumping the current pointer, and comparing it against the limit.
If ParentAllocator
is different from NullAllocator
, Region
deallocates the chunk of memory during destruction.
The minAlign
parameter establishes alignment. If minAlign > 1
, the sizes of all allocation requests are rounded up to a multiple of minAlign
. Applications aiming at maximum speed may want to choose minAlign = 1
and control alignment externally.
import std.algorithm.comparison : max; import std.experimental.allocator.building_blocks.allocator_list : AllocatorList; import std.experimental.allocator.mallocator : Mallocator; import std.typecons : Ternary; // Create a scalable list of regions. Each gets at least 1MB at a time by // using malloc. auto batchAllocator = AllocatorList!( (size_t n) => Region!Mallocator(max(n, 1024 * 1024)) )(); writeln(batchAllocator.empty); // Ternary.yes auto b = batchAllocator.allocate(101); writeln(b.length); // 101 writeln(batchAllocator.empty); // Ternary.no // This will cause a second allocation b = batchAllocator.allocate(2 * 1024 * 1024); writeln(b.length); // 2 * 1024 * 1024 // Destructor will free the memory
The parent allocator. Depending on whether ParentAllocator
holds state or not, this is a member variable or an alias for ParentAllocator.instance
.
Constructs a region backed by a user-provided store. Assumes the memory was allocated with ParentAllocator
(if different from NullAllocator
).
ubyte[] store
| User-provided store backing up the region. If ParentAllocator is different from NullAllocator , memory is assumed to have been allocated with ParentAllocator . |
size_t n
| Bytes to allocate using ParentAllocator . This constructor is only defined If ParentAllocator is different from NullAllocator . If parent.allocate(n) returns null , the region will be initialized as empty (correctly initialized but unable to allocate). |
Rounds the given size to a multiple of the alignment
Alignment offered.
Allocates n
bytes of memory. The shortest path involves an alignment adjustment (if alignment > 1
), an increment, and a comparison.
size_t n
| number of bytes to allocate |
n
or null
if request could not be satisfied.Allocates n
bytes of memory aligned at alignment a
.
size_t n
| number of bytes to allocate |
uint a
| alignment for the allocated block |
n
bytes aligned at a
, or null
.Allocates and returns all memory available to this region.
Expands an allocated block in place. Expansion will succeed only if the block is the last allocated. Defined only if growDownwards
is No.growDownwards
.
Deallocates b
. This works only if b
was obtained as the last call to allocate
; otherwise (i.e. another allocation has occurred since) it does nothing.
void[] b
| Block previously obtained by a call to allocate against this allocator (null is allowed). |
Deallocates all memory allocated by this region, which can be subsequently reused for new allocations.
Queries whether b
has been allocated with this region.
void[] b
| Arbitrary block of memory (null is allowed; owns(null) returns false ). |
true
if b
has been allocated with this region, false
otherwise.Returns Ternary.yes
if no memory has been allocated in this region, Ternary.no
otherwise. (Never returns Ternary.unknown
.)
Nonstandard property that returns bytes available for allocation.
InSituRegion
is a convenient region that carries its storage within itself (in the form of a statically-sized array).
The first template argument is the size of the region and the second is the needed alignment. Depending on the alignment requested and platform details, the actual available storage may be smaller than the compile-time parameter. To make sure that at least n
bytes are available in the region, use InSituRegion!(n + a - 1, a)
.
Given that the most frequent use of InSituRegion
is as a stack allocator, it allocates starting at the end on systems where stack grows downwards, such that hot memory is used first.
// 128KB region, allocated to x86's cache line InSituRegion!(128 * 1024, 16) r1; auto a1 = r1.allocate(101); writeln(a1.length); // 101 // 128KB region, with fallback to the garbage collector. import std.experimental.allocator.building_blocks.fallback_allocator : FallbackAllocator; import std.experimental.allocator.building_blocks.free_list : FreeList; import std.experimental.allocator.building_blocks.bitmapped_block : BitmappedBlock; import std.experimental.allocator.gc_allocator : GCAllocator; FallbackAllocator!(InSituRegion!(128 * 1024), GCAllocator) r2; const a2 = r2.allocate(102); writeln(a2.length); // 102 // Reap with GC fallback. InSituRegion!(128 * 1024, 8) tmp3; FallbackAllocator!(BitmappedBlock!(64, 8), GCAllocator) r3; r3.primary = BitmappedBlock!(64, 8)(cast(ubyte[]) (tmp3.allocateAll())); const a3 = r3.allocate(103); writeln(a3.length); // 103 // Reap/GC with a freelist for small objects up to 16 bytes. InSituRegion!(128 * 1024, 64) tmp4; FreeList!(FallbackAllocator!(BitmappedBlock!(64, 64), GCAllocator), 0, 16) r4; r4.parent.primary = BitmappedBlock!(64, 64)(cast(ubyte[]) (tmp4.allocateAll())); const a4 = r4.allocate(104); writeln(a4.length); // 104
An alias for minAlign
, which must be a valid alignment (nonzero power of 2). The start of the region and all allocation requests will be rounded up to a multiple of the alignment.
InSituRegion!(4096) a1; assert(a1.alignment == platformAlignment); InSituRegion!(4096, 64) a2; assert(a2.alignment == 64);
Allocates bytes
and returns them, or null
if the region cannot accommodate the request. For efficiency reasons, if bytes == 0
the function returns an empty non-null slice.
As above, but the memory allocated is aligned at a
bytes.
Deallocates b
. This works only if b
was obtained as the last call to allocate
; otherwise (i.e. another allocation has occurred since) it does nothing. This semantics is tricky and therefore deallocate
is defined only if Region
is instantiated with Yes.defineDeallocate
as the third template argument.
void[] b
| Block previously obtained by a call to allocate against this allocator (null is allowed). |
Returns Ternary.yes
if b
is the result of a previous allocation, Ternary.no
otherwise.
Expands an allocated block in place. Expansion will succeed only if the block is the last allocated.
Deallocates all memory allocated with this allocator.
Allocates all memory available with this allocator.
Nonstandard function that returns the bytes available for allocation.
Allocator backed by sbrk
for Posix systems. Due to the fact that sbrk
is not thread-safe by design, SbrkRegion
uses a mutex internally. This implies that uncontrolled calls to brk
and sbrk
may affect the workings of SbrkRegion
adversely.
Instance shared by all callers.
Standard allocator primitives.
Rounds the given size to a multiple of thew alignment
The expand
method may only succeed if the argument is the last block allocated. In that case, expand
attempts to push the break pointer to the right.
The deallocate
method only works (and returns true
) on systems that support reducing the break address (i.e. accept calls to sbrk
with negative offsets). OSX does not accept such. In addition the argument must be the last block allocated.
The deallocateAll
method only works (and returns true
) on systems that support reducing the break address (i.e. accept calls to sbrk
with negative offsets). OSX does not accept such.
Standard allocator API.
The threadsafe version of the Region
allocator. Allocations and deallocations are lock-free based using core.atomic.cas
.
The parent allocator. Depending on whether ParentAllocator
holds state or not, this is a member variable or an alias for ParentAllocator.instance
.
Constructs a region backed by a user-provided store. Assumes the memory was allocated with ParentAllocator
(if different from NullAllocator
).
ubyte[] store
| User-provided store backing up the region. If ParentAllocator is different from NullAllocator , memory is assumed to have been allocated with ParentAllocator . |
size_t n
| Bytes to allocate using ParentAllocator . This constructor is only defined If ParentAllocator is different from NullAllocator . If parent.allocate(n) returns null , the region will be initialized as empty (correctly initialized but unable to allocate). |
Rounds the given size to a multiple of the alignment
Alignment offered.
Allocates n
bytes of memory. The allocation is served by atomically incrementing a pointer which keeps track of the current used space.
size_t n
| number of bytes to allocate |
n
, or null
if request could not be satisfied.Deallocates b
. This works only if b
was obtained as the last call to allocate
; otherwise (i.e. another allocation has occurred since) it does nothing.
void[] b
| Block previously obtained by a call to allocate against this allocator (null is allowed). |
Deallocates all memory allocated by this region, which can be subsequently reused for new allocations.
Allocates n
bytes of memory aligned at alignment a
.
size_t n
| number of bytes to allocate |
uint a
| alignment for the allocated block |
n
bytes aligned at a
, or null
.Queries whether b
has been allocated with this region.
void[] b
| Arbitrary block of memory (null is allowed; owns(null) returns false ). |
true
if b
has been allocated with this region, false
otherwise.Returns Ternary.yes
if no memory has been allocated in this region, Ternary.no
otherwise. (Never returns Ternary.unknown
.)
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Licensed under the Boost License 1.0.
https://dlang.org/phobos/std_experimental_allocator_building_blocks_region.html