We Keep Coding

C# MessageBox in a loop [duplicate]

I have been attempting to have a re-usable modal progress window (I.e. progressForm.ShowDialog()) to show progress from a running async task, including enabling cancellation.
I have seen some implementations that launch start the async task by hooking the Activated event handler on the form, but I need to start the task first, then show the modal dialog that will show it's progress, and then have the modal dialog close when completed or cancellation is completed (note - I want the form closed when cancellation is completed - signalled to close from the task continuation).
I currently have the following - and although this working - are there issues with this - or could this be done in a better way?
I did read that I need to run this CTRL-F5, without debugging (to avoid the AggregateException stopping the debugger in the continuation - and let it be caught in the try catch as in production code)
ProgressForm.cs
- Form with ProgressBar (progressBar1) and Button (btnCancel)
public partial class ProgressForm : Form
{
public ProgressForm()
{
InitializeComponent();
}
public event Action Cancelled;
private void btnCancel_Click(object sender, EventArgs e)
{
if (Cancelled != null) Cancelled();
}
public void UpdateProgress(int progressInfo)
{
this.progressBar1.Value = progressInfo;
}
}
Services.cs
- Class file containing logic consumed by WinForms app (as well as console app)
public class MyService
{
public async Task<bool> DoSomethingWithResult(
int arg, CancellationToken token, IProgress<int> progress)
{
// Note: arg value would normally be an
// object with meaningful input args (Request)
// un-quote this to test exception occuring.
//throw new Exception("Something bad happened.");
// Procressing would normally be several Async calls, such as ...
// reading a file (e.g. await ReadAsync)
// Then processing it (CPU instensive, await Task.Run),
// and then updating a database (await UpdateAsync)
// Just using Delay here to provide sample,
// using arg as delay, doing that 100 times.
for (int i = 0; i < 100; i++)
{
token.ThrowIfCancellationRequested();
await Task.Delay(arg);
progress.Report(i + 1);
}
// return value would be an object with meaningful results (Response)
return true;
}
}
MainForm.cs
- Form with Button (btnDo).
public partial class MainForm : Form
{
public MainForm()
{
InitializeComponent();
}
private async void btnDo_Click(object sender, EventArgs e)
{
CancellationTokenSource cts = new CancellationTokenSource();
CancellationToken token = cts.Token;
// Create the ProgressForm, and hook up the cancellation to it.
ProgressForm progressForm = new ProgressForm();
progressForm.Cancelled += () => cts.Cancel();
// Create the progress reporter - and have it update
// the form directly (if form is valid (not disposed))
Action<int> progressHandlerAction = (progressInfo) =>
{
if (!progressForm.IsDisposed) // don't attempt to use disposed form
progressForm.UpdateProgress(progressInfo);
};
Progress<int> progress = new Progress<int>(progressHandlerAction);
// start the task, and continue back on UI thread to close ProgressForm
Task<bool> responseTask
= MyService.DoSomethingWithResultAsync(100, token, progress)
.ContinueWith(p =>
{
if (!progressForm.IsDisposed) // don't attempt to close disposed form
progressForm.Close();
return p.Result;
}, TaskScheduler.FromCurrentSynchronizationContext());
Debug.WriteLine("Before ShowDialog");
// only show progressForm if
if (!progressForm.IsDisposed) // don't attempt to use disposed form
progressForm.ShowDialog();
Debug.WriteLine("After ShowDialog");
bool response = false;
// await for the task to complete, get the response,
// and check for cancellation and exceptions
try
{
response = await responseTask;
MessageBox.Show("Result = " + response.ToString());
}
catch (AggregateException ae)
{
if (ae.InnerException is OperationCanceledException)
Debug.WriteLine("Cancelled");
else
{
StringBuilder sb = new StringBuilder();
foreach (var ie in ae.InnerExceptions)
{
sb.AppendLine(ie.Message);
}
MessageBox.Show(sb.ToString());
}
}
finally
{
// Do I need to double check the form is closed?
if (!progressForm.IsDisposed)
progressForm.Close();
}
}
}
Modified code - using TaskCompletionSource as recommended...
private async void btnDo_Click(object sender, EventArgs e)
{
bool? response = null;
string errorMessage = null;
using (CancellationTokenSource cts = new CancellationTokenSource())
{
using (ProgressForm2 progressForm = new ProgressForm2())
{
progressForm.Cancelled +=
() => cts.Cancel();
var dialogReadyTcs = new TaskCompletionSource<object>();
progressForm.Shown +=
(sX, eX) => dialogReadyTcs.TrySetResult(null);
var dialogTask = Task.Factory.StartNew(
() =>progressForm.ShowDialog(this),
cts.Token,
TaskCreationOptions.None,
TaskScheduler.FromCurrentSynchronizationContext());
await dialogReadyTcs.Task;
Progress<int> progress = new Progress<int>(
(progressInfo) => progressForm.UpdateProgress(progressInfo));
try
{
response = await MyService.DoSomethingWithResultAsync(50, cts.Token, progress);
}
catch (OperationCanceledException) { } // Cancelled
catch (Exception ex)
{
errorMessage = ex.Message;
}
finally
{
progressForm.Close();
}
await dialogTask;
}
}
if (response != null) // Success - have valid response
MessageBox.Show("MainForm: Result = " + response.ToString());
else // Faulted
if (errorMessage != null) MessageBox.Show(errorMessage);
}

I think the biggest issue I have, is that using await (instead of
ContinueWith) means I can't use ShowDialog because both are blocking
calls. If I call ShowDialog first the code is blocked at that point,
and the progress form needs to actually start the async method (which
is what I want to avoid). If I call await
MyService.DoSomethingWithResultAsync first, then this blocks and I
can't then show my progress form.
The ShowDialog is indeed a blocking API in the sense it doesn't return until the dialog has been closed. But it is non-blocking in the sense it continues to pump messages, albeit on a new nested message loop. We can utilize this behavior with async/await and TaskCompletionSource:
private async void btnDo_Click(object sender, EventArgs e)
{
CancellationTokenSource cts = new CancellationTokenSource();
CancellationToken token = cts.Token;
// Create the ProgressForm, and hook up the cancellation to it.
ProgressForm progressForm = new ProgressForm();
progressForm.Cancelled += () => cts.Cancel();
var dialogReadyTcs = new TaskCompletionSource<object>();
progressForm.Load += (sX, eX) => dialogReadyTcs.TrySetResult(true);
// show the dialog asynchronousy
var dialogTask = Task.Factory.StartNew(
() => progressForm.ShowDialog(),
token,
TaskCreationOptions.None,
TaskScheduler.FromCurrentSynchronizationContext());
// await to make sure the dialog is ready
await dialogReadyTcs.Task;
// continue on a new nested message loop,
// which has been started by progressForm.ShowDialog()
// Create the progress reporter - and have it update
// the form directly (if form is valid (not disposed))
Action<int> progressHandlerAction = (progressInfo) =>
{
if (!progressForm.IsDisposed) // don't attempt to use disposed form
progressForm.UpdateProgress(progressInfo);
};
Progress<int> progress = new Progress<int>(progressHandlerAction);
try
{
// await the worker task
var taskResult = await MyService.DoSomethingWithResultAsync(100, token, progress);
}
catch (Exception ex)
{
while (ex is AggregateException)
ex = ex.InnerException;
if (!(ex is OperationCanceledException))
MessageBox.Show(ex.Message); // report the error
}
if (!progressForm.IsDisposed && progressForm.Visible)
progressForm.Close();
// this make sure showDialog returns and the nested message loop is over
await dialogTask;
}

Why is My Async Timer Blocking the UI Thread?

I have a timer setup in my mainwindow code behind that fires every ten seconds. Because some of the code referenced in the timer_Elapsed event is somewhat CPU intensive I have placed it inside an await Task.Run(() =>, however the UI thread continues to hang momentarily whenever the elapsed event runs. Any ideas why this would be blocking the UI? Code:
async void _timer_Elapsed(object sender, ElapsedEventArgs e)
{
await Task.Run(() =>
{
//Update default status bar text routinely
try
{
if (ChecEnabled())
{
this.Dispatcher.Invoke(() =>
{
StatusText.Text = String.Format("Status: Enabled. Watching for changes…");
});
}
else
{
this.Dispatcher.Invoke(() =>
{
StatusText.Text = String.Format("Status: Disabled");
});
}
}
catch (ObjectDisposedException)
{
//Window closed and disposed timer on different thread
}
//System Checks
UpdateSystemReadyStatus();
});
}

Update your Invoke to InvokeAsync. Also, do you really need to entire method wrapped in a Task?
async void _timer_Elapsed(object sender, ElapsedEventArgs e)
{
//Update default status bar text routinely
try
{
if (ChecEnabled())
{
await this.Dispatcher.InvokeAsync(() =>
{
StatusText.Text = String.Format("Status: Enabled. Watching for changes…");
});
}
else
{
await this.Dispatcher.InvokeAsync(() =>
{
StatusText.Text = String.Format("Status: Disabled");
});
}
}
catch (ObjectDisposedException)
{
//Window closed and disposed timer on different thread
}
//System Checks
await Task.Run(()=>UpdateSystemReadyStatus());
}

C# .NET - Using Background Thread but GUI is Unresponsive

I'm implementing a Client who can ask a service for a certain action and also an abort button for this action.
Once I run the action using background thread the abort button should become active, but instead the entire GUI is stuck with the mouse icon as hour glass (Should mention that the action is still indeed occurring).
private void actionButton_Click(object sender, EventArgs e)
{
Run(RunMode.Action);
}
private void Run(RunMode runMode)
{
abortButton.Enabled = true;
try
{
var name = "ds_file";
var url = UrlProvider.BuildRequestUrl(runMode, name);
StartLoading($"Running request: {url}");
RunWorker(url);
}
catch (Exception ex)
{
AddToLog(ex.ToString());
PopError("Failed to run, see error in log box");
}
}
private void RunWorker(string url)
{
var worker = new BackgroundWorker();
worker.DoWork += (sender, args) =>
{
DatabaseHelper.DisableAllJobs();
HttpRequestsHandler.HttpGet(url);
DatabaseHelper.EnableRegularJobs();
};
worker.RunWorkerCompleted += (sender, args) =>
{
StopLoading();
abortButton.Enabled = false;
if (args.Error != null)
{
PopError("Failed to run, see error in log box");
AddToLog(args.Error.ToString());
}
else
{
PopInfo("Completed successfully");
}
};
worker.RunWorkerAsync();
}
What am I doing wrong?
Thanks

Following example run background service every 10 seconds to update GUI. You can modify it as you wish. By running your thread as async task your GUI never get hang.
public frm_testform()
{
InitializeComponent();
dispatcherTimer_Tick().DoNotAwait();
}
private async Task dispatcherTimer_Tick()
{
DispatcherTimer timer = new DispatcherTimer();
TaskCompletionSource<bool> tcs = null;
EventHandler tickHandler = (s, e) => tcs.TrySetResult(true);
timer.Interval = TimeSpan.FromSeconds(10);
timer.Tick += tickHandler;
timer.Start();
while (true)
{
tcs = new TaskCompletionSource<bool>();
await Task.Run(() =>
{
// Run your background service and UI update here
await tcs.Task;
}
}

It indeed turns out I had controls.enable = false in some part of the code (I really thought it totally meant for something else), thank you all for your help!!

Thread pass data and window close

I have created a simple WPF project where on button click I create a separate thread with new window, and pass data to it. On application Exit I am trying to close safely that thread/window. However, I get occasionally the bellow exception, which causes application instabilities.
So my question is how to handle that situation gracefully. Thx
On line:
Dispatcher.Invoke(new Action(() =>
I have
A first chance exception of type 'System.Threading.ThreadAbortException' occurred in mscorlib.dll
Additional information: Thread was being aborted.
My View has the following code:
Constructor
public MyView(ConcurrentQueue<MyItem> actionReports, ManualResetEvent actionCompletedEvent, string actionName)
{
_actionReports = actionReports;
_actionCompletedEvent = actionCompletedEvent;
_actionName = actionName;
InitializeComponent();
DataContext = this;
this.Loaded += MyView_Loaded;
}
void MyView_Loaded(object sender, RoutedEventArgs e)
{
var worker = new BackgroundWorker();
worker.DoWork += (o, ea) =>
{
while (true)
{
if (_actionCompletedEvent.WaitOne(0))
{
// Issue
Dispatcher.Invoke(new Action(() =>
{
Close();
}));
Thread.Sleep(100);
}
while (!_actionReports.IsEmpty)
{
// Do some stuff
}
}
};
worker.RunWorkerAsync();
}
Initialize of Window
public WindowLauncher(ManualResetEvent actionCompletedEvent, ManualResetEvent reportWindowClosedEvent, string actionName)
{
_actionCompletedEvent = actionCompletedEvent;
_reportWindowClosedEvent = reportWindowClosedEvent;
_actionName = actionName;
Thread thread = new Thread(new ThreadStart(() =>
{
_reportWindow = new MyView(_messageQueue, _actionCompletedEvent, actionName);
_reportWindow.Show();
// InvokeShutdown to terminate the thread properly
_reportWindow.Closed += (sender, args) =>
{
_reportWindow.Dispatcher.InvokeShutdown();
};
_resetEvent.Set();
Dispatcher.Run();
}));
thread.Name = "MyWindowThread";
thread.SetApartmentState(ApartmentState.STA);
thread.IsBackground = true;
thread.Start();
}

I'd normally at least try to cancel the BackgroundWorker async action in the Window.OnClosing event and catch the pending cancellation. You'll still need to watch out for ThreadAbortExceptions but only if your async process is long-running.
private BackgroundWorker _worker;
private void MyView_Loaded(object sender, RoutedEventArgs e)
{
_worker = new BackgroundWorker();
_worker.WorkerSupportsCancellation = true;
_worker.DoWork += (o, ea) =>
{
while (true)
{
if (_actionCompletedEvent.WaitOne(0))
{
if (_worker.CancellationPending)
{
ea.Cancel = true;
return;
}
// Issue
Dispatcher.Invoke(new Action(() =>
{
Close();
}));
Thread.Sleep(100);
}
while (!_actionReports.IsEmpty)
{
// Do some stuff
}
}
};
}
protected override void OnClosing(CancelEventArgs e)
{
_worker.CancelAsync();
}

Background threads are aborted automatically by the runtime when your app exits. Normally they do not throw ThreadAbortExceptions (see Foreground and Background threads)
Invoking the dispatcher causes a method to be run on the dispatch thread, but since you used Invoke() rather than BeginInvoke(), the dispatcher needs to inform the background thread that the method finished. I suspect this is where the exception is being raised, but this is only conjecture on my part.
Try catching the exception like this:
try
{
Dispatcher.Invoke(new Action(() =>
{
Close();
}));
}
catch (ThreadAbortException)
{
Thread.ResetAbort();
}
Although this may not help if the exception is being raised on the dispatch thread. If this doesn't work then try BeginInvoke() instead.
BTW, you can probably reproduce this bug more easily if you stick some kind of delay in the start of your Invoked lambda and close the app at that point. That means the background thread will be aborted by the time the lambda completes.

Pausing a new BackGroundWorker until previous completes

I am struggling with threading.
The problem is when I am iterating trough foreach loop.
When setting this.Document, the application performs login, that is triggered with an event and takes few seconds to complete. In the worker_RunWorkerCompleted method I need to perform some actions that depend on current login information.
The problem is that before I can perform this action for the first file, the this.Document already changes making the application perform another login. This way I can never actually perform my actions.
My question is: How can I pause the next thread until previous thread has completed.
Is there any other solution to my problem?
I tried with AutoResetEvent but I got no luck. I set waitOne() just after the RunWorkerAsync call and .Set() in the RunWorkerCompleted. The code never gets to RunWorkerCompleted...
Here is the code:
public void Start(object obj)
{
try
{
foreach (KeyValuePair<string, Stream> pair in this.CollectionOfFiles)
{
Worker = new BackgroundWorker();
Worker.DoWork += new DoWorkEventHandler(worker_DoWork);
Worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);
using (Stream stream = pair.Value)
{
primaryDocument = new Document(stream);
DataHolderClass dataHolder = new DataHolderClass();
dataHolder.FileName = pair.Key;
dataHolder.Doc = secondaryDocument;
//background thread call
Worker.RunWorkerAsync(dataHolder);
}
}
}
catch (Exception ex)
{
// exception logic
}
finally
{
// complete logic
}
}
private void worker_DoWork(object sender, DoWorkEventArgs e)
{
DataHolderClass dataHolder = ((DataHolderClass)e.Argument);
// setting this attribute triggers execution of login event
this.Document = dataHolder.Doc;
e.Result = (dataHolder);
}
private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
// here I need to perform some actions that are depending on the current login
DataHolderClass dataHolder = ((DataHolderClass)e.Result);
this.eventAggregator.GetEvent<ActionEvent>().Publish(new Message(EMessageType.Info) { Title = dataHolder.FileName });
}

no9,
Try the following:
System.Threading.ManualResetEvent _busy = new System.Threading.ManualResetEvent(false);
void ResumeWorker()
{
// Start the worker if it isn't running
if (!backgroundWorker1.IsBusy) backgroundWorker1.RunWorkerAsync(dataHolder);
// Unblock the worker
_busy.Set();
}
void PauseWorker()
{
// Block the worker
_busy.Reset();
}
void CancelWorker()
{
if (backgroundWorker1.IsBusy) {
// Set CancellationPending property to true
backgroundWorker1.CancelAsync();
// Unblock worker so it can see that
_busy.Set();
}
}
then in your code run the method.
Let me know if it works :)

class SimpleWaitPulse
{
static readonly object _locker = new object();
static bool _go;
static void Main()
{ // The new thread will block
new Thread (Work).Start(); // because _go==false.
Console.ReadLine(); // Wait for user to hit Enter
lock (_locker) // Let's now wake up the thread by
{ // setting _go=true and pulsing.
_go = true;
Monitor.Pulse (_locker);
}
}
static void Work()
{
lock (_locker)
while (!_go)
Monitor.Wait (_locker); // Lock is released while we’re waiting
Console.WriteLine ("Woken!!!");
}
}
Can you use pulse ?
Taken from : Threading in C# from albahari.com

Well, the design is terrible... but if you need to stick to it, you can set wait handles in a previous worker and wait for it in next. This is the minimal fix, still quite an abomination:
public void Start(object obj)
{
try
{
BackgroundWorker previousWorker = null;
DataHolderClass previousWorkerParams = null;
foreach (KeyValuePair<string, Stream> pair in this.CollectionOfFiles)
{
// signal event on previous worker RunWorkerCompleted event
AutoResetEvent waitUntilCompleted = null;
if (previousWorker != null)
{
waitUntilCompleted = new AutoResetEvent(false);
previousWorker.RunWorkerCompleted += (o, e) => waitUntilCompleted.Set();
// start the previous worker
previousWorker.RunWorkerAsync(previousWorkerParams);
}
Worker = new BackgroundWorker();
Worker.DoWork += (o, e) =>
{
// wait for the handle, if there is anything to wait for
if (waitUntilCompleted != null)
{
waitUntilCompleted.WaitOne();
waitUntilCompleted.Dispose();
}
worker_DoWork(o, e);
};
using (Stream stream = pair.Value)
{
primaryDocument = new Document(stream);
DataHolderClass dataHolder = new DataHolderClass();
dataHolder.FileName = pair.Key;
dataHolder.Doc = secondaryDocument;
// defer running this worker; we don't want it to finish
// before adding additional completed handler
previousWorkerParams = dataHolder;
}
previousWorker = Worker;
}
if (previousWorker != null)
{
previousWorker.RunWorkerAsync(previousWorkerParams);
}
}
catch (Exception ex)
{
// exception logic
}
finally
{
// complete logic
}
}