What's the best way to pass data between concurrent threads in .NET?

Question

I have two threads, one needs to poll a bunch of separate static resources looking for updates. The other one needs to get the data and store it in the database. How can thread 1 tell thread 2 that there is something to process?

Answer 1

If the pieces of data are independant then treat the pieces of data as work items to be processed by a pool of threads. Use the thread pool and QueueUserWorkItem to post the data to the thread(s). You should get better scalability using a pool of symmetric threads and limiting the amount of synchronisation that has to occur between the producer and consumer(s).

For example (from MSDN):

    TaskInfo ti = new TaskInfo("This report displays the number {0}.", 42);

    // Queue the task and data.
    if (ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc), ti)) {    
        Console.WriteLine("Main thread does some work, then sleeps.");

        // If you comment out the Sleep, the main thread exits before
        // the ThreadPool task has a chance to run.  ThreadPool uses 
        // background threads, which do not keep the application 
        // running.  (This is a simple example of a race condition.)
        Thread.Sleep(1000);

        Console.WriteLine("Main thread exits.");
    }
    else {
        Console.WriteLine("Unable to queue ThreadPool request."); 
    }


// The thread procedure performs the independent task, in this case
// formatting and printing a very simple report.
//
static void ThreadProc(Object stateInfo) {
    TaskInfo ti = (TaskInfo) stateInfo;
    Console.WriteLine(ti.Boilerplate, ti.Value); 
}

Answer 2

I use Monitor.Wait / Pulse on a Queue of work items.