Question: could I use this library to implement a fixed number of shared locks

[alastairtree]

I have a requirement to implement a distributed lock for a fixed number of clients, so the lock should allow for say 5 clients to acquire the lock, but the sixth client lock acquisition attempt should fail. Any suggestions for implementing this with this library? Thanks!

[madelson]

Hi @alastairtree thanks for your interest in the library.

It sounds like what you are really looking for is a distributed semaphore. You may be interested in the discussion on this topic here: #7

In short, there is no automated way to do this with the current library although I am very interested in building one in if we can find a robust and performant implementation. Since you need only 5 concurrent clients, you could likely get away with simply looping over a set of 5 locks until one of them works:

class SqlDistributedSemaphore {
     private readonly IReadOnlyList<SqlDistributedLock> _locks;

     public SqlDistributedSemaphore(string lockName, int maxCount) 
     {
        this._locks = Enumerable.Range(0, maxCount).Select(i => new SqlDistributedLock(..., lockName: lockName + maxCount)).ToArray();
     }

     public IDisposable Acquire()
     {
            Random random = null;
            while (true)
            {
                for (var i = 0; i < this._locks.Count; ++i)
                {
                     var handle = this._locks[i].TryAcquire();
                     if (handle != null) { return handle; }
                }

                Thread.Sleep((random ?? random = new Random()).Next(50));
            }
     }
}

[madelson]

Duplicate of #7

[alastairtree]

Super useful answer, thank you!