Updating fields of values in a ConcurrentDictionary

Question

I am trying to update entries in a ConcurrentDictionary something like this:

class Class1
{
    public int Counter { get; set; }
}

class Test
{
    private          


        

Answer 1

First, to solve your locking problem:

class Class1
{
    // this must be a variable so that we can pass it by ref into Interlocked.Increment.
    private int counter;

    public int Counter
    {
        get{return counter; }
    }

    public void Increment()
    {
        // this is about as thread safe as you can get.
        // From MSDN: Increments a specified variable and stores the result, as an atomic operation.
        Interlocked.Increment(ref counter);

        // you can return the result of Increment if you want the new value,
        //but DO NOT set the counter to the result :[i.e. counter = Interlocked.Increment(ref counter);] This will break the atomicity.
    }
}

Iterating the just values should be faster than iterating the key value pair. [Though I think iterating a list of keys and doing the look-ups will be faster still on the ConcurrentDictionary in most situations.]

class Test
{
    private ConcurrentDictionary dictionary = new ConcurrentDictionary();

    public void TestIt()
    {
        foreach (var foo in dictionary.Values)
        {
            foo.Increment();
        }
    }

    public void TestItParallel()
    {
        Parallel.ForEach(dictionary.Values,x=>x.Increment() );
    }

}