Monitoring Progress in Parallel.ForEach

Question

Attempting to monitor progress of a Parallel.ForEach loop I have tried the suggestion put forward in this question but unfortunately I have still been unable to accomplish what I wanted.

Basically the first problem I ran into when I attempted the implementation suggested (using a timer) was that the Parallel.ForEach method is a blocking call and hence the timer-tick callback was not occurring.

So I tried putting the Parallel.ForEach loop inside of a background worker thread. Which did infact allow for the timer-tick event to occur but my counter value is never updated until the ForEach operation is complete.

Here is the basic idea of the code (with the backgroundworker).

private StockList _StockListToProcess = null;

private static Int64 ItemsProcessed = 0;

private System.Windows.Threading.DispatcherTimer _timer = null;

private System.ComponentModel.BackgroundWorker _backWorker = null;

progressBar1.Minimum = 1;
progressBar1.Maximum = this._StockListToProcess.Count;

MainWindow.ItemsProcessed = 0;

this._timer = new System.Windows.Threading.DispatcherTimer();
this._timer.Interval = TimeSpan.FromMilliseconds(100);
this._timer.Tick += timer_Tick;
this._timer.Start();

this._backWorker = new System.ComponentModel.BackgroundWorker();

this._backWorker.DoWork += delegate(object o, System.ComponentModel.DoWorkEventArgs args)
{
    Parallel.ForEach(this._StockListToProcess, new ParallelOptions() { MaxDegreeOfParallelism = 5 },
                     (Stock stock) =>
                         {
                             MyWebServiceClient serviceClient = new MyWebServiceClient ();
                             MyWebServiceClient.ResponseEnum result = (MyWebServiceClient .ResponseEnum)serviceClient.SetProductPricing(token.LoginName, token.LoginPassword, token.SiteID.ToString(), stock.ProductCode, stock.ProductPrice);
                             System.Threading.Interlocked.Increment(ref MainWindow.ItemsProcessed);
                         });

    this._timer.Stop();
};

private void timer_Tick(object sender, EventArgs e)
{
    progressBar1.Value = MainWindow.ItemsProcessed;
}

What am I missing?

Solution 1

Although I do appreciate the solution posted by Enigmativity after some searching I have found what I consider the correct implementation for solving this problem. One that does not require any other frameworks to implement.

For a full overview please see this article.

Solution 2

I'm going to take a stab at saying the nesting of timers and background workers is causing you grief.

If possible, I suggest you avoid then in favour of using the Reactive Extensions for .NET (Rx).

This is what your code would look like if you did:

progressBar1.Minimum = 1;
progressBar1.Maximum = this._StockListToProcess.Count;

var itemsProcessed = 0;
var updater = new Subject<Unit>(Scheduler.Dispatcher);
updater.Subscribe(u =>
{
    itemsProcessed += 1; //Rx serializes "OnNext" calls so this is safe.
    progressBar1.Value = itemsProcessed;
});

Parallel.ForEach(this._StockListToProcess, new ParallelOptions() { MaxDegreeOfParallelism = 5 },
    (Stock stock) =>
        {
            MyWebServiceClient serviceClient = new MyWebServiceClient ();
            MyWebServiceClient.ResponseEnum result = (MyWebServiceClient .ResponseEnum)serviceClient.SetProductPricing(token.LoginName, token.LoginPassword, token.SiteID.ToString(), stock.ProductCode, stock.ProductPrice);
            updater.OnNext(new Unit());
        });

updater.OnCompleted();

I did a test using a dummy bit of code and it worked fine so, if you are brave enough, you should be able to get this running without to much difficulty. :-)