or (recommended):

var asyncKeyedLocker = new AsyncKeyedLocker<string>();

or if you would like to set the maximum number of requests for the semaphore that can be granted concurrently (set to 1 by default):

var asyncKeyedLocker = new AsyncKeyedLocker<string>(2);

There are also AsyncKeyedLocker<TKey>() constructors which accept the parameters of ConcurrentDictionary, namely the concurrency level, the capacity and the IEqualityComparer<TKey> to use.

Locking

using (var lockObj = await asyncKeyedLocker.LockAsync(myObject))
{
	...
}

There are other overloaded methods for LockAsync which allow you to use CancellationToken, milliseconds timeout, System.TimeSpan or a combination of these. In the case of timeouts, you can also use TryLockAsync methods which will call a Func<Task> or Action if the timeout is not expired, whilst returning a boolean representing whether or not it waited successfully.

There are also synchronous Lock methods available, including out parameters for checking whether or not the timeout was reached.

If you would like to see how many concurrent requests there are for a semaphore for a given key:

int myRemainingCount = asyncKeyedLocker.GetRemainingCount(myObject);

If you would like to see the number of remaining threads that can enter the lock for a given key:

int myCurrentCount = asyncKeyedLocker.GetCurrentCount(myObject);

If you would like to check whether any request is using a specific key:

bool isInUse = asyncKeyedLocker.IsInUse(myObject);

Credits

This library was inspired by Stephen Cleary's solution.