Crate lockbell 

lockbell

An RwLock that rings back when contention clears.

The problem

RwLock::try_write returns None when the lock is contended — and gives you no way to know when it becomes free. You’re left choosing between spinning, blocking, or silently dropping work.

The solution

use lockbell::RwLockBell;

let lock = RwLockBell::new(0u32);

// Holds the lock — any concurrent try_write_or will register a callback
let guard = lock.write();

// Fails: lock is held. Callback is queued.
lock.try_write_or(|| println!("lock is free now"));

// Dropping the guard fires all queued callbacks in FIFO order.
drop(guard);

When try_write_or fails, the callback is queued. Queued callbacks are flushed in FIFO order — without holding any lock — when either:

• a write guard is dropped, or
• the last active read guard is dropped (if callbacks were queued while readers held the lock).

try_write_or_else is also available when constructing the callback is expensive and should only happen on contention.

Callback semantics

• Callbacks run after the lock is released, in registration order.
• A callback is a notification, not a lock acquisition — the lock may already be re-acquired by the time the callback fires.
• Callbacks must be FnOnce() + Send + 'static.
• A panicking callback does not prevent subsequent callbacks from running.

Installation

[dependencies]
lockbell = "0.1"

Use cases

• Lazy invalidation: a thread that loses the write race registers a callback to invalidate a local cache entry once the winner finishes.
• Coalesced work: multiple producers collapse concurrent write attempts into a single update, with each loser notified on completion.
• Write-through coordination: trigger downstream work (logging, metrics, replication) exactly once per write, regardless of contention.

Structs

MappedRwLockBellReadGuard

RAII read guard produced by RwLockBellReadGuard::map and related methods.

MappedRwLockBellWriteGuard

RAII write guard produced by RwLockBellWriteGuard::map and related methods.

RwLockBell

An RwLock wrapper that fires registered callbacks when a write guard is released.

RwLockBellReadGuard

RAII read guard for RwLockBell.

RwLockBellWriteGuard

RAII write guard for RwLockBell.