ArcRwLockT

ArcRwLockT is a name commonly used in Rust projects to denote a shared, mutable value guarded by an atomically reference-counted pointer to a read-write lock, i.e., Arc<RwLock<T>>. This pattern combines thread-safe ownership with interior mutability, enabling safe access to a value from multiple threads.

Arc provides thread-safe reference counting, allowing several owners to share the same locked data. RwLock offers concurrent read access: multiple readers can hold the read lock simultaneously, while writers acquire exclusive access. This makes Arc<RwLock<T>> suitable for workloads with many readers and relatively few writers.

Typical usage involves creating a value protected by a lock and sharing the Arc across threads. For example, let data = Arc::new(RwLock::new(initial)); let data2 = Arc::clone(&data); In a reader thread, acquire a read lock with data.read(), yielding a RwLockReadGuard from which you can read without mutation. In a writer thread, acquire a write lock with data.write(), yielding a RwLockWriteGuard that allows mutation. Guards are released automatically when dropped, and the Arc ensures proper deallocation when all clones are dropped.

Lock poisoning is an important consideration: if a thread panics while holding a lock, the lock can become poisoned, causing subsequent lock attempts to fail until handling is performed. The standard API returns PoisonError on such attempts, which can be unwrapped or handled explicitly. Downgrading a write lock back to a read lock is possible via the downgrade method on the write guard, though deadlocks remain a risk if locks are held too long.

ArcRwLockT is best suited for read-heavy concurrent access patterns where safe shared ownership is required across threads. Alternatives include Arc<Mutex<T>> for simpler exclusive access or other concurrency primitives for specialized workloads.