Crate rclite

RcLite: small, fast, and memory-friendly reference counting

RcLite is a lightweight reference-counting solution for Rust that serves as an alternative to the standard library’s reference-counting. It offers both multi-threaded and single-threaded reference counting options with improved performance and reduced memory overhead, boasting at least 50% and up to 100% decrease in memory overhead compared to the standard library reference counting. RcLite is a suitable option when weak references are not necessary and optimizing for performance and memory usage is a priority.

Why use RcLite?

• It’s faster and smaller
• Uses less memory
• It provides a lightweight drop-in replacements for standard library std::sync::Arc and std::rc::Rc
• It supports no_std with extern alloc

Why not use RcLite?

• It does not provide weak references
• It does not support data as DSTs
• With RcLite in 64-bit systems, you only can have 4,294,967,296 - 256 live references to an object which requires about 32GBs of ram for holding all these references to this single object location. if you need to have 18,446,744,073,709,551,616 live references to an object, use the standard library. In other systems with smaller pointer sizes like 32-bit, you will have usize::MAX live references limitation that is the same as the standard library.

Comparison

	rclite::{Arc,Rc}	std::*::{Arc,Rc}
Overhead in 64-bit systems	4 bytes	16 bytes
Overhead in 32-bit systems	4 or 2 bytes	8 bytes
Overhead in 16-bit systems	2 or 1 bytes	4 bytes
Weak References	❌	✅
DST Support	❌	✅

In 64-bit systems, RcLite has an advantage over the standard library’s Arc as it can utilize the memory padding area, using only 4 bytes to store the counter. This results in a reduction in memory usage, as there is less memory waste on padding. However, in situations where there is not enough padding available in the structure, RcLite will have an overhead of 8 bytes, which is still half of the standard library’s overhead.

For instance, in 64-bit systems, Rc<u32> and Arc<u32> allocate the same amount of memory as Box<u32>, since the Box<u32> allocation will be padded to u64 by the allocator.

In 32-bit and 16-bit systems, the memory overhead of the RcLite will be 50% of the standard library.

Features

By default, RcLite uses a counter size of half the word size for 64-bit systems, with the usize-for-small-platforms feature enabled. This is because overflowing a 32-bit counter is harder compared to overflowing 16-bit counters. If you wish to use the half register size on other platforms, you can disable the default features by setting default-features = false. This will result in the use of 16-bit counters on 32-bit platforms and 8-bit counters on 16-bit platforms.

Structs

• Arc
  The Arc<T> type represents a thread-safe reference-counting pointer, where “Arc” stands for “Atomically Reference Counted”. It provides shared ownership of a value of type T, stored on the heap. When you call the clone method on Arc, a new instance of Arc is created that points to the same heap allocation as the original Arc, and the reference count is increased. Once the last Arc pointer to a given allocation is destroyed, the inner value stored in that allocation is also dropped.
• Rc
  Rc<T> is a reference-counting pointer for single-threaded use, for multi-threaded use cases you should use Arc<T>. Rc<T> provides shared ownership of a value of type T that is stored in the heap. When you clone an Rc, it creates a new pointer to the same heap allocation. When the last Rc pointer to the allocation is destroyed, the stored value is also dropped.