Soenneker.Asyncs.Locks

The fastest .NET async lock

This library provides a single primitive: AsyncLock.

Design goal

AsyncLock is built to be the fastest possible correct mutex for real-world .NET systems.

It provides the following guarantees:

Cancellation-safe

• Fully supports cancellation before acquisition and while waiting for both async and sync callers.
• Cancelled waiters are removed immediately, never resumed, and never leaked — with zero impact on the fast path.

Unified async + sync locking

• Async and synchronous callers share the same mutex.
• Ordering is preserved without adapters, wrappers, or duplicated synchronization primitives.

Performance (by design)

• Uncontended acquisition is as close to a single atomic operation as possible
• No allocations, tasks, or state machines unless contention occurs
• Cancellation and disposal logic are completely excluded from the fast path
• Deterministic behavior under contention

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Installation

dotnet add package Soenneker.Asyncs.Locks

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Usage

Async

await using (await _lock.Lock(ct))
{
    // critical section
}

Sync

using (_lock.LockSync())
{
    // critical section
}

Try-lock

if (_lock.TryLock(out var releaser))
{
    using (releaser)
    {
        // critical section
    }
}

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Benchmarks

Async lock acquisition

Method	Mean	Error	StdDev	Median	Ratio