Question

I’m trying to implement multi-threading as suggested here: Spawn Multiple Threads for work then wait until all finished

Code looks like so:

var resetEvent = new ManualResetEvent(false);
            var clientsCount = IDLocal.UserSessions.Count;

            // Load sessions:
            IDLocal.UserSessions = new IDSessions();

            // Start thread for each client 
            foreach (IDSession session in IDLocal.UserSessions)
            {
                var clnt = session;
                new Thread(
                    delegate()
                    {
                        Debug.WriteLine(Thread.CurrentThread.ManagedThreadId);
                        clnt.FailedToRespond = !this.SendDirect(data, this.GetHostAddress(clnt.HostName), clnt.PortNumber);

                        // If we're the last thread, signal 
                        if (Interlocked.Decrement(ref clientsCount) == 0) resetEvent.Set();
                    })
                    .Start();
            }

Here I’m getting ReSharper warning: if (Interlocked.Decrement(ref clientsCount) == 0)

It suggests that I’m accessing modified closure (clientsCount)

Is that a valid suggestion?

Answer 1

The warning is meant to cover code such as

int i = 1;
Func<int> f = () => i + 1;
i = 2;
int j = f(); // What does this set j to?

where the updated value of i will be used when calling f. The warning suggests to change this to

int i = 1;
int icopy = i;
Func<int> f = () => icopy + 1;
i = 2;
int j = f(); // Now what does this set j to?

if you want f to see the value of i as it was when the delegate was created. In the context of foreach loops, it is very easy to otherwise get unintuitive behaviour. There has been a change in the meaning of foreach loops in C# 5 because of exactly this.

Since that’s not what you want here, since you do want to see changes to the captured variable, don’t change anything in the code.