[−][src]Crate shared_arena
For more details visit shared-arena's repository:
https://github.com/sebastiencs/shared-arena
Memory pools are usefull when allocating and deallocating lots of
data of the same size.
Using a memory pool speed up those allocations/deallocations.
This crate provides 3 memory pools:
Performance
On my laptop, with Intel i7-6560U, running Clear Linux OS 32700,
an allocation with SharedArena is 4+ faster than the
system allocator:
Allocation/SharedArena time: [25.112 ns 25.678 ns 26.275 ns] Allocation/Box(SystemAllocator) time: [112.64 ns 114.44 ns 115.81 ns]
Implementation details
SharedArena, Arena and Pool use the same method of allocation,
derived from a free list.
They allocate by pages, which include 63 elements, and keep a list
of pages where at least 1 element is not used by the user.
A page has a bitfield of 64 bits, each bit indicates whether or
not the element is used.
In this bitfield, if the bit is set to zero, the element is
already used.
So counting the number of trailing zeros gives us the index of an
unused element.
Only 1 cpu instruction is necessary to find an unused element:
such as tzcnt/bsf on x86 and clz on arm
[..]1101101000With the bitfield above, the 4th element is unused.
The difference between SharedArena/Arena and Pool is that
Pool does not use atomics.
Allocating with Pool is faster than SharedArena and Arena.
Arena is faster than SharedArena
Safety
unsafe block are used in several places to dereference pointers.
The code is 100% covered
by the miri interpreter,
valgrind and 3 sanitizers: address, leak and memory, on each commit.
See the github actions
Structs
| Arena | An arena |
| ArenaArc | A reference-counting pointer to |
| ArenaBox | A pointer to |
| ArenaRc | A single threaded reference-counting pointer to |
| Pool | A single threaded arena |
| PoolBox | A pointer to |
| SharedArena | An arena shareable across threads |