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#195 in Concurrency

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Trc is a performant heap-allocated smart pointer for Rust that implements thread reference counting. Trc stands for: Thread Reference Counted. Trc provides a shared ownership of the data similar to Arc<T> and Rc<T>. It implements thread reference counting, which is based on the observation that most objects are only used by one thread. This means that two reference counts can be created: one for thread-local use, and one atomic one for sharing between threads. Thread reference counting sets the atomic reference count to the number of threads using the data.

A cycle between Trc pointers cannot be deallocated as the reference counts will never reach zero. The solution is a Weak<T>. A Weak<T> is a non-owning reference to the data held by a Trc<T>. They break reference cycles by adding a layer of indirection and act as an observer. They cannot access the data directly, and must be converted back into a Trc. Weak does not keep the value alive (which can be dropped), and only keeps the backing allocation alive.

To soundly implement thread safety Trc is !Send and !Sync. To solve this, Trc introduces a SharedTrc<T>, which is Send and Sync. SharedTrc is the only way to safely send a Trc's data across threads without using a Weak. See SharedTrc for it's API, which is similar to that of Weak.

Because Trc is not part of the standard library, the CoerceUnsized and Receiver traits cannot currently be implemented by default. However, Trc provides dyn_unstable trait which enables the above traits for Trc and SharedTrc and must be used with nightly Rust (cargo +nightly ...).


See examples here.


Click here for more benchmarks. Multiple different operating systems, CPUs, and architectures are tested.

Trc vs Arc performance


To use Trc, simply run cargo add trc, or add trc = "1.2.3". Optionally, you can always use the latest version by adding trc = {git = "https://github.com/EricLBuehler/trc.git"}.