AsyncKeyedLock

An asynchronous .NET Standard 2.0 library that allows you to lock based on a key (keyed semaphores), limiting concurrent threads sharing the same key to a specified number, with optional pooling for reducing memory allocations.

For example, suppose you were processing financial transactions, but while working on one account you wouldn't want to concurrently process a transaction for the same account. Of course, you could just add a normal lock, but then you can only process one transaction at a time. If you're processing a transaction for account A, you may want to also be processing a separate transaction for account B. That's where AsyncKeyedLock comes in: it allows you to lock but only if the key matches.

The library uses two very different methods for locking, one using an underlying ConcurrentDictionary that's cleaned up after use whilst the other using a technique called striped locking. Both have their advantages and disadvantages, and in order to help you choose you are highly recommended to read about it in the wiki.

A simple non-keyed lock is also available through AsyncNonKeyedLocker.

Installation and usage

Using this library is straightforward. Here's a simple example:

private static readonly AsyncKeyedLocker<string> _asyncKeyedLocker = new(o =>
  {
    o.PoolSize = 20; // this is NOT a concurrency limit
    o.PoolInitialFill = 1;
  });

...

using (await _asyncKeyedLocker.LockAsync("test123"))
{
  ...
}

Please read the full documentation in our wiki for help in using this libary.

Benchmarks

This library has been extensively benchmarked against several other options and our benchmarks run publicly and transparently on Github Actions.

When striped locking is an option, the StripedAsyncKeyedLocker consistently beats any other option in terms of both speed as well as memory allocations.

When the traditional dictionary-based method is used, AsyncKeyedLocker with pooling provides a great balance in terms of speed and memory allocations, which is an excellent, safe go-to solution.

Credits

Check out our list of contributors!