Question

I implemented threading in my application for scraping websites. After all the sites are scraped I want to process them.

form creates queueworker(which creates 2 workers and processes tasks). After all the tasks are done I want to process them baack in the formthread. At this point I accieved this with

public void WaitForCompletion()     {         // Enqueue one null task per worker to make each exit.         StopWorkers();                  //wait for the workers to finish         foreach (Thread worker in workers)         {             worker.Join();         }     } 

After a task is preformed I fire (from queueworker):

public event EventHandler<ProgressEvent> UrlScanned;      if (UrlScanned != null) {           UrlScanned(this, new ProgressEvent(task.Name, 1)); } 

And catch that event with:

urlscanner.UrlScanned += new EventHandler<ProgressEvent>(UrlScanningProgress);       private void UrlScanningProgress(object sender, ProgressEvent args) {    if (pbarurlScan.InvokeRequired)    {        //don't use invoke when Thread.Join() is used! Deadlock        Invoke(new MethodInvoker(delegate() { UrlScanningProgress(sender, args);         //BeginInvoke(new MethodInvoker(delegate() { UrlScanningProgress(sender, args)};    }    else    {                 pbarurlScan.Value++;    } } 

The problem is that the formthread gets blocked and with calling Invoke the whole application is now in a deadlock situation.

How can I give update to the formthread without having a deadlock and have an immidiate update (begininvoke occurs if the workers threads are done)

Answer 1

Why are you doing the Join? I would raise a callback at the end of each thread – perhaps decrementing a counter. When the counter gets to 0, then call back to the UI thread and do the ‘all done’ code; something like:

using System.Windows.Forms; using System.Threading; using System; class MyForm : Form {      public MyForm()     {         Button btn = new Button();         Controls.Add(btn);         btn.Text = 'Go';         btn.Click += btn_Click;     }     int counter;     void btn_Click(object sender, System.EventArgs e)     {         for (int i = 0; i < 5; i++)         {             Interlocked.Increment(ref counter);             ThreadPool.QueueUserWorkItem(DoWork, i);         }     }     void DoWork(object state)     {         for (int i = 0; i < 10; i++)         { // send progress             BeginInvoke((Action)delegate { Text += state.ToString(); });             Thread.Sleep(500);         }         EndThread(); // this thread done     }     void EndThread()     {         if (Interlocked.Decrement(ref counter) == 0)         {             AllDone();         }     }     void AllDone()     {         Invoke((Action)delegate { this.Text += ' all done!'; });     }     [STAThread]     static void Main()     {         Application.Run(new MyForm());     } }