Question

There is a sequence for FORM(some UI) should get downloaded using service.
Currently, this download is in a BackgroundWorker Thread.
Now, since the performance is slow… We decided to categories the FORMS into 2 and start downloading parallely using another BackgroundWorker on top of the existing Thread.

Now, the scenario is the either of this BackgroundWorker should wait for other to complete.
So, how to implement it.

I tried with AutoResetEvent. but, i could not achieve this.

Any help is appreciated.

Answer 1

I don’t think that the scenario is really that one BackgroundWorker should wait for another. What you really want is to fire some UI event after (and only after) both of them complete. It’s a subtle but important difference; the second version is a lot easier to code.

public class Form1 : Form
{
    private object download1Result;
    private object download2Result;

    private void BeginDownload()
    {
        // Next two lines are only necessary if this is called multiple times
        download1Result = null;
        download2Result = null;

        bwDownload1.RunWorkerAsync();
        bwDownload2.RunWorkerAsync();
    }

    private void bwDownload1_RunWorkerCompleted(object sender,
        RunWorkerCompletedEventArgs e)
    {
        download1Result = e.Result;
        if (download2Result != null)
            DisplayResults();
    }

    private void bwDownload2_RunWorkerCompleted(object sender,
        RunWorkerCompletedEventArgs e)
    {
        download2Result = e.Result;
        if (download1Result != null)
            DisplayResults();
    }

    private void DisplayResults()
    {
        // Do something with download1Result and download2Result
    }
}

Note that those object references should be strongly-typed, I just used object because I don’t know what you’re downloading.

This is really all you need; the RunWorkerCompleted event runs in the foreground thread so you actually don’t need to worry about synchronization or race conditions in there. No need for lock statements, AutoResetEvent, etc. Just use two member variables to hold the results, or two boolean flags if the result of either can actually be null.