2 releases
0.1.1 | Dec 16, 2023 |
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0.1.0 | Dec 2, 2023 |
#377 in Memory management
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ref_arena
A no_std
(alloc) arena that acts similarly to a Slab<Rc<T>>
but with
better performance and less features.
This arena stores reference counts with the objects in
a continuous buffer, which decreases the need for
multiple small memory allocations. References can
be cloned and act like normal Rc
s. When all references
to an object is dropped, the space is made available
for a new object, and if the arena is dropped, the
underlying buffer may also be dropped.
This arena features constant time inserts, derefs, and drops while allocating less often, decreasing memory fragmentation, having increased performance (depending on the allocator), and potentially using less memory.
RefArena
does not support Weak references and probably
will not in the indefinite future.
This library uses a decent amount of unsafe code, and is partially tested with miri. It should be safe since the code isn't too complex, but beware of bugs.
Example
use ref_arena::{RefArena, RcRef};
let mut arena: RefArena<i32> = RefArena::new();
// Create a reference
let reference: RcRef<i32> = arena.insert(5);
// Deref to get the inner value
let inner = *reference;
assert_eq!(inner, 5);
// We can create clones of the reference just like an Rc!
let clone = reference.clone();
assert_eq!(*clone, 5);
// References can be held even after the arena is dropped.
drop(arena);
assert_eq!(*reference, 5);
// Objects (and internal buffers) are dropped when
// all references are dropped.
drop(reference);
drop(clone);
Benchmarks
Note: These benchmarks are very specific and cater to the creation of lots of small objects.
Additionally these benchmarks may vary system-to-system and allocator-to-allocator.
Allocating 10k Rc
s:
std::rc::Rc allocate 10_000 247.59 μs
RefArena allocate 10_000 48.57 μs
~5x speedup
Dereferencing 10k Rc
s:
std::rc::Rc deref 10_000 4.97 μs
RefArena deref 10_000 4.86 μs
no speedup
Dereferencing should be about the same within both since it's a simple pointer dereference.
Dropping 10k Rc
s:
std::rc::Rc drop 10_000 134.35 μs
RefArena drop 10_000 29.06 μs
~4.62x speedup
Reallocating 10k Rc
s:
RefArena realloc 10_000 45.62 μs
In this case 10k RcRef
s were allocated and dropped, and we measured
the time it took to put 10k objects back onto the arena.
(Compare to allocate)
Comparison to rc_arena
rc_arena
is similar to ref_arena
in that they are arenas that return reference counted objects.
Both contain inner buffers that hold contiguous lists of objects.
The main difference between the two is that rc_arena
does not
individually count objects. When all references of an object are
dropped in ref_arena
, the inner object is dropped and the space
is made available for a new insertion (similar to slab
and
stable-vec
), whereas in rc_arena
the space is never made available again.
rc_arena
is useful if you have a determinite amount of objects
that need to be reference counted, where ref_arena
is useful
when you frequently create and drop objects.
Note this comparison might not be 100% correct as it's just
what I could tell from looking at the code and documentation.
Additionally this crate was not made with rc_arena
in mind.
License: MIT