Thread-safe memoization

Question

Let\'s take Wes Dyer\'s approach to function memoization as the starting point:

public static Func Memoize(this Func f)
{         


        

Answer 1

Expanding on Nigel Touch's excellent answer, I wanted to offer a reusable component extracted from his solution limiting the invocation count for f(a).

I called it SynchronizedConcurrentDictionary, and it looks like this:

public class SynchronizedConcurrentDictionary : ConcurrentDictionary
{
    private readonly ReaderWriterLockSlim _cacheLock = new ReaderWriterLockSlim();

    public new TValue GetOrAdd(TKey key, Func valueFactory)
    {
        TValue result;

        _cacheLock.EnterWriteLock();
        try
        {
            result = base.GetOrAdd(key, valueFactory);
        }
        finally
        {
            _cacheLock.ExitWriteLock();
        }

        return result;
    }
}

Then the Memoize function becomes a two-liner:

public static Func Memoize(this Func f)
{
    var cache = new SynchronizedConcurrentDictionary();

    return key => cache.GetOrAdd(key, f);
}

Cheers!