ArcMutexTT

ArcMutexTT is a concurrency primitive that provides shared ownership with interior mutability for a value of type T. It combines an atomic reference-counted pointer (Arc) with a mutual exclusion lock (Mutex), allowing multiple threads to access and mutate the same data safely. The TT suffix identifies a variant that adds transactional semantics or time-travel-like capabilities, depending on the implementation. In its simplest form, ArcMutexTT behaves like an Arc-wrapped Mutex around T.

Design: The core consists of a value of type T protected by a mutex, with the whole structure reference-counted by Arc. Cloning the Arc shares ownership and increments the count; any thread must acquire the inner lock to read or modify the value. The transactional variant provides an API to execute a group of operations within a transaction, then commit or roll back based on conflicts.

API and usage: Typical operations include new(value) to construct, clone() to share, and lock() to obtain a guard granting access to T. If a transaction API is provided, there are begin_transaction(), read_set(), write_set(), and commit_transaction() calls, enabling batched updates with conflict detection. Best practices emphasize short critical sections and avoiding long-running transactions.

Performance considerations: ArcMutexTT incurs the costs of reference counting and mutex contention. It is generally suitable when there are many readers and infrequent mutations, or when transactional grouping reduces contention by batching changes.

Limitations: The implementation may suffer from mutex poisoning on panics, potential deadlocks with improper usage, and overhead compared to more specialized synchronization primitives. Compatibility and guarantees depend on the specific library.

See also: Arc, Mutex, ReadWriteLock, Transactional memory.