I have initiated some async infinite loops in my WinForm application, but each time I am trying to break out of them, the program hangs up. I have read some similar topics where people suggested using CancellationTokens, but I am not able to adapt them to my needs. Here is the relevant part of my code.
static bool processStop = false;
static bool processStopped = false;
//Called once
private async void ProcessData()
{
while (!processStop)
{
await Task.Run
(
() =>
{
//Do stuff and call regular not async methods
}
);
}
processStopped = true;
}
//Button click handler to exit WinForm
btnExit.Click += (senders, args) =>
{
processStop = true;
//Programm hangs up here
while (!processStopped);
FormMain.Close();
}
Edited the code
The variables are static.
The Close method is the default Close() method for Forms.
The problem is that the call to Task.Run continues on the main thread. processStop = true; and while (!processStopped); execute synchronously one after the other. This doesn't let the ProcessData method continue its execution and a deadlock occures.
I see a couple of solutions:
Use ConfigureAwait(false) with Task.Run:
private async void ProcessData()
{
while (!processStop)
{
await Task.Run
(
() =>
{
//Do stuff and call regular not async methods
}
).ConfigureAwait(false);
}
processStopped = true;
}
This will cause the ProcessData to continue on a thread pool and you already use a thread pool by calling Task.Run, so it is not a great solution
Wrap the whole process in Task.Run:
static volatile bool processStop = false;
static volatile bool processStopped = false;
//Called once
private async void ProcessData()
{
await Task.Run(() =>
{
while (!processStop)
{
...
}
processStopped = true;
});
}
This would require changing the form of the method passed to work with the loop in it.
Make ProcessData a synchronous method to process CPU-intensive tasks and call it properly. CancellationToken would be the preferred way to cancel the task:
private void ProcessData(CancellationToken token)
{
while(!token.IsCancellationRequested)
{
// do work
}
}
And call it with this:
Task processingTask;
CancellationTokenSource cts;
void StartProcessing()
{
cts = new CancellationTokenSource();
processingTask = Task.Run(() => ProcessData(cts.Token), cts.Token);
}
btnExit.Click += async (senders, args) =>
{
cts.Cancel();
try
{
await processingTask;
}
finally
{
FormMain.Close();
}
}
If you want to spin a bunch of tasks without blocking you can do this:
using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsApp1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
//Called once
private async Task ProcessData()
{
int count = 0;
while (true)
{
await Task.Run
(
() =>
{
this.Invoke(new Action(() => {
label2.Text = (count++).ToString();
label1.Text = DateTime.Now.ToString(); }));
Thread.Sleep(100);
}
);
}
Debugger.Break(); //you will never see this hit at all
}
private void button1_Click(object sender, EventArgs e)
{
this.Close();
}
private async void button2_Click(object sender, EventArgs e)
{
await ProcessData();
}
}
}
Related
I want to start / stop a thread in order not to block the UI using button
public partial class Program_Form : Form
{
readonly BackgroundWorker m_oWorker;
[STAThread]
private void Program_Form_Load(object sender, EventArgs e)
{
// long code here
}
private async void DGW6BtnPrint_Click(object sender, EventArgs e)
{
Work.Printer_ Print = new Work.Printer_();
await Task.Run(() =>
{
Print.Print_File(this, dataGridView6, StatusText, progressBar1,
varriablesStatus);
});
}
public void BTN6PPauza_Click(object sender, EventArgs e)
{
//What i had tried
//_canceller.Dispose();
//_canceller.Cancel();
// varriablesStatus = false;
//thread2.break;
//autoResetEvent.WaitOne();
//thread2.Join();
//_manualResetEvent.Reset();
//thread2.Abort();
//_pauseEvent.Reset();
//varriablesStatus = "Pause";
//Print_Actions();
}
}
Referenced class:
namespace OfficeTools.Work
{
class Printer_
{
public void Print_File(Program_Form callForm, DataGridView DGW,
TextBox Status, ProgressBar Progress, bool varriablesStatus)
{
foreach (DataGridViewRow Row in DGW.Rows)
{
file = DGW.Rows[Row.Index].Cells[4].Value.ToString();
PrintFiles.Print_Word(file);
}
}
}
}
How can I start stop pause resume the thread because nothing worked from what I had tried, I think the problem is from the foreach loop
I never used threads, and I can not find an example similar with mine in order to understand how should I do.
What you are asking implies that you want to use the Thread.Suspend and Thread.Resume methods. Possibly like this:
private volatile Thread _printThread;
private async void DGW6BtnPrint_Click(object sender, EventArgs e)
{
Work.Printer_ Print = new Work.Printer_();
await Task.Run(() =>
{
_printThread = Thread.CurrentThread;
try
{
Print.Print_File(this, dataGridView6, StatusText, progressBar1,
varriablesStatus);
}
finally { _printThread = null; }
});
}
public void BTN6PPauza_Click(object sender, EventArgs e)
{
var printThread = _printThread;
if (printThread != null)
{
if (printThread.ThreadState.HasFlag(ThreadState.Running))
{
printThread.Suspend();
}
else if (printThread.ThreadState.HasFlag(ThreadState.Suspended))
{
printThread.Resume();
}
}
}
The documentation of these two methods includes several cautionary warnings that discourage usage:
Thread.Suspend has been deprecated. Use other classes in System.Threading, such as Monitor, Mutex, Event, and Semaphore, to synchronize Threads or protect resources.
Do not use the Suspend and Resume methods to synchronize the activities of threads. You have no way of knowing what code a thread is executing when you suspend it. If you suspend a thread while it holds locks during a security permission evaluation, other threads in the AppDomain might be blocked. If you suspend a thread while it is executing a class constructor, other threads in the AppDomain that attempt to use that class are blocked. Deadlocks can occur very easily.
It's up to you if you want to accept these risks. If you ask me, you shouldn't.
Note: The Suspend and Resume methods are not supported on .NET Core and later platforms. On these platforms they throw a PlatformNotSupportedException exception. You can use them only if you target the .NET Framework platform.
i made this work, i do not know if it is the right way but for the moment it works
public partial class Program_Form : Form
{
readonly BackgroundWorker m_oWorker;
CancellationTokenSource _tokenSource = null;
[STAThread]
private void Program_Form_Load(object sender, EventArgs e)
{
// long code here
}
private async void DGW6BtnPrint_Click(object sender, EventArgs e)
{
_tokenSource = new CancellationTokenSource();
var token = _tokenSource.Token;
Work.Printer_ Print = new Work.Printer_();
await Task.Run(() =>
{
Print.Print_File(this, dataGridView6, StatusText, progressBar1, token);
});
}
public void BTN6PPauza_Click(object sender, EventArgs e)
{
_tokenSource.Cancel();
}
}
Referenced class:
namespace OfficeTools.Work
{
class Printer_
{
public void Print_File(Program_Form callForm, DataGridView DGW, TextBox Status, ProgressBar Progress, CancellationToken Token)
{
foreach (DataGridViewRow Row in DGW.Rows)
{
file = DGW.Rows[Row.Index].Cells[4].Value.ToString();
PrintFiles.Print_Word(file);
if (Token.IsCancellationRequested)
{
try
{
Winword.Quit(ref missing, ref missing, ref missing);
winword = null;
}
catch { }
return;
}
}
}
}
}
Kind regards all
thanks for reading this topic.
For a new WPF application (build in C#) I have a question regarding the design.
The past few days I have read a lot about Async programming in C# (based on .NET 4.5).
What we would like to do is: Create a new async thread, which does independent background tasks. When this thread has data available: then send this data to the main program (by an public interface). So, the thread will set data in the main program and immediately return to the thread again. The main program will raise an event (INotifyPropertyChanged) when data has been changed.
What will be the best way to create this Async thread? Or at least, what would be the best way to design this feature?
At the moment I have build an application which creates a thread.
This does not work Async at the moment:
public MainWindow()
{
InitializeComponent();
InitGuiInterface(this);
//Create thread
new OuterLabel_Thread(this);
}
And the class "OuterLabel_Thread.cs"here below:
public class OuterLabel_Thread
{
private MainWindow context = null;
private bool exit = false;
private int count = 0;
public OuterLabel_Thread(MainWindow context)
{
this.context = context;
Console.WriteLine("Running sample thread");
Thread thread = new Thread(delegate ()
{
Console.WriteLine("Sample thread started");
//start new task
//run();
Task.Factory.StartNew(run);
});
thread.Start();
}
public void Exit()
{
exit = true;
}
private void run()
{
while (!exit)
{
DateTime Time1 = DateTime.Now;
if (context != null && context.GuiInterface != null)
{
//context.GuiInterface.UpdateThreadCount(count, "label_code_content");
}
Console.WriteLine("Background thread count = " + count);
count++;
if (count > 1000)
{
exit = true;
}
//Console.WriteLine((DateTime.Now - Time1).TotalMilliseconds.ToString());
Thread.Sleep(10);
}
}
}
Many thanks in advance!
Kind regards,
Rein.
as you want to keep the thread alive and as far as I understand, you don't know exactly when or if you will reach the 1000 mark, async might be the wrong choice. Correct me if i'm wrong.
For your case I would recommend using the BackgroundWorker:
private void BackgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
int count = 0;
BackgroundWorker worker = sender as BackgroundWorker;
while (!exit)
{
DateTime Time1 = DateTime.Now;
worker.ReportProgress(count);
count++;
if (count > 1000)
{
exit = true;
}
Thread.Sleep(10);
}
}
// This event handler updates the progress.
private void BackgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
resultLabel.Text = ("Background thread count = " + e.ProgressPercentage.ToString());
}
private void BackgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Cancelled == true)
{
resultLabel.Text = "Canceled!";
}
else if (e.Error != null)
{
resultLabel.Text = "Error: " + e.Error.Message;
}
else
{
resultLabel.Text = "Done!";
}
}
The best way would be using async+await and tasks.
private async void LaunchButton_OnClick(object sender, RoutedEventArgs e)
{
resultLabel.Content = "Task running";
resultLabel.Content = await SomeLongRunningTaskAsync();
}
private Task<string> SomeLongRunningTaskAsync()
{
return Task.Run(
() =>
{
// Put your background work in here. with Task.Run it's not going to run on UI
int count = 0;
while (count < 1000)
{
count++;
Thread.Sleep(10);
}
return "Task done";
});
}
I can't figure out if you are looking for a service or a long running task.
Since the others have good examples of long running tasks I've made a Service
It uses some advanced concpets like SynchronizationContext that you should read up on before using this in production code. Google async await and Stephen Cleary.
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
var foo = new FooService();
foo.StartService(); // UI thrad calling
}
}
public class FooService
{
private SynchronizationContext _context;
private CancellationTokenSource _cts;
private CancellationToken _token;
private Task _task;
public void StartService()
{
_context = SynchronizationContext.Current; // Depends on the UI thread being the one to start the service or this will fail
_cts = new CancellationTokenSource(10000); // Run for 10 seconds
_token = _cts.Token;
_task = Task.Run(() => Run(), _token);
}
public async Task Stop()
{
_cts.Cancel();
await _task; // wait for task to finish
}
private void Run()
{
while (!_token.IsCancellationRequested)
{
// Do work
Thread.Sleep(1000);
// Alternative use Control.Invoke() if you have access to a UI element, to delegate to the UI thread
_context.Send((id) => Console.WriteLine($"Delegate from thread {id} to thread {Thread.CurrentThread.ManagedThreadId}"), Thread.CurrentThread.ManagedThreadId);
}
}
}
My constructor besides other things call another method DoWork
public MyTask(TaskAction action)
{
DoWork(action);
}
DoWork method goes to another method Calc(2)
private void Calc (int 2){
... calc and save result into file
}
How can I alert MyTask that Calc is done and let MyTask to continue further.
P.S. I could read hdd every few secs in order to see whether file with result is save and based on that continue further, but I assume that there is better way.
BackgroundWorker class allows you to easily manage your async work.
BackgroundWorker _worker = new BackgroundWorker();
public Cnt()
{
InitializeComponent();
_worker.DoWork += WorkerOnDoWork;
_worker.RunWorkerCompleted += WorkerOnRunWorkerCompleted;
//start your work
_worker.RunWorkerAsync();
}
private void WorkerOnRunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
//Worker completed event
}
private void WorkerOnDoWork(object sender, DoWorkEventArgs e)
{
//Do
}
There are many ways to do this.The latest recommended is using tasks
Task taskA = new Task(() => { Console.WriteLine("Task A started"); });
taskA.ContinueWith((ss) => { Console.WriteLine("Task A finished"); });
taskA.Start();
http://msdn.microsoft.com/en-us/library/ee372288(v=vs.110).aspx
This way you can block the current thread if you want.
Another way is the BackGroundWorker Class
Also, you can use a custom callback like this
using System;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
DoWorkA(DoWorkFinished);
Console.Read();
}
private static void DoWorkA(Action whatToDoWhenFinished)
{
Console.WriteLine("Doing something");
whatToDoWhenFinished();
}
private static void DoWorkFinished()
{
Console.WriteLine("Doing something Else");
}
}
}
I have the following code in a WinForms application with one button and one label:
using System;
using System.IO;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private async void button1_Click(object sender, EventArgs e)
{
await Run();
}
private async Task Run()
{
await Task.Run(async () => {
await File.AppendText("temp.dat").WriteAsync("a");
label1.Text = "test";
});
}
}
}
This is a simplified version of the real application I'm working on. I was under the impression that by using async/await in my Task.Run I could set the label1.Text property. However, when running this code I get the error that I'm not on the UI thread and I can't access the control.
Why can't I access the label control?
When you use Task.Run(), you're saing that you don't want the code to run on the current context, so that's exactly what happens.
But there is no need to use Task.Run() in your code. Correctly written async methods won't block the current thread, so you can use them from the UI thread directly. If you do that, await will make sure the method resumes back on the UI thread.
This means that if you write your code like this, it will work:
private async void button1_Click(object sender, EventArgs e)
{
await Run();
}
private async Task Run()
{
await File.AppendText("temp.dat").WriteAsync("a");
label1.Text = "test";
}
Try this:
replace
label1.Text = "test";
with
SetLabel1Text("test");
and add the following to your class:
private void SetLabel1Text(string text)
{
if (InvokeRequired)
{
Invoke((Action<string>)SetLabel1Text, text);
return;
}
label1.Text = text;
}
The InvokeRequired returns true if you are NOT on the UI thread. The Invoke() method takes the delegate and parameters, switches to the UI thread and then calls the method recursively. You return after the Invoke() call because the method has already been called recursively prior to the Invoke() returning. If you happen to be on the UI thread when the method is called, the InvokeRequired is false and the assignment is performed directly.
Try this
private async Task Run()
{
await Task.Run(async () => {
await File.AppendText("temp.dat").WriteAsync("a");
});
label1.Text = "test";
}
Or
private async Task Run()
{
await File.AppendText("temp.dat").WriteAsync("a");
label1.Text = "test";
}
Or
private async Task Run()
{
var task = Task.Run(async () => {
await File.AppendText("temp.dat").WriteAsync("a");
});
var continuation = task.ContinueWith(antecedent=> label1.Text = "test",TaskScheduler.FromCurrentSynchronizationContext());
await task;//I think await here is redundant
}
async/await doesn't guarantee that it will run in UI thread. await will capture the current SynchronizationContext and continues execution with the captured context once the task completed.
So in your case you have a nested await which is inside Task.Run hence second await will capture the context which is not going to be UiSynchronizationContext because it is being executed by WorkerThread from ThreadPool.
Does this answers your question?
Why do you use Task.Run? that start a new worker thread (cpu bound), and it causes your problem.
you should probably just do that:
private async Task Run()
{
await File.AppendText("temp.dat").WriteAsync("a");
label1.Text = "test";
}
await ensure you will continue on the same context except if you use .ConfigureAwait(false);
Because it's on a different thread and cross-thread calls aren't allowed.
You will need to pass on the "context" to the thread you are starting. See an example here: http://reedcopsey.com/2009/11/17/synchronizing-net-4-tasks-with-the-ui-thread/
I am going to give you my latest answer that I have given for async understanding.
The solution is as you know that when you are calling async method you need to run as a task.
Here is a quick console app code that you can use for your reference, it will make it easy for you to understand the concept.
using System;
using System.Threading;
using System.Threading.Tasks;
public class Program
{
public static void Main()
{
Console.WriteLine("Starting Send Mail Async Task");
Task task = new Task(SendMessage);
task.Start();
Console.WriteLine("Update Database");
UpdateDatabase();
while (true)
{
// dummy wait for background send mail.
if (task.Status == TaskStatus.RanToCompletion)
{
break;
}
}
}
public static async void SendMessage()
{
// Calls to TaskOfTResult_MethodAsync
Task<bool> returnedTaskTResult = MailSenderAsync();
bool result = await returnedTaskTResult;
if (result)
{
UpdateDatabase();
}
Console.WriteLine("Mail Sent!");
}
private static void UpdateDatabase()
{
for (var i = 1; i < 1000; i++) ;
Console.WriteLine("Database Updated!");
}
private static async Task<bool> MailSenderAsync()
{
Console.WriteLine("Send Mail Start.");
for (var i = 1; i < 1000000000; i++) ;
return true;
}
}
Here I am trying to initiate task called send mail. Interim I want to update database, while the background is performing send mail task.
Once the database update has happened, it is waiting for the send mail task to be completed. However, with this approach it is quite clear that I can run task at the background and still proceed with original (main) thread.
I've gotten this type of thing working in the past with a BackgroundWorker, but I want to use the new async/await approach of .NET 4.5. I may be barking up the wrong tree. Please advise.
Goal: Create a component that will do some long-running work and show a modal form with a progress bar as it's doing the work. The component will get the handle to a window to block interaction while it's executing the long-running work.
Status: See the code below. I thought I was doing well until I tried interacting with the windows. If I leave things alone (i.e. don't touch!), everything runs "perfectly", but if I do so much as click on either window the program hangs after the long-running work ends. Actual interactions (dragging) are ignored as though the UI thread is blocked.
Questions: Can my code be fixed fairly easily? If so, how? Or, should I be using a different approach (e.g. BackgroundWorker)?
Code (Form1 is a standard form with a ProgressBar and a public method, UpdateProgress, that sets the ProgressBar's Value):
using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Starting..");
var mgr = new Manager();
mgr.GoAsync();
Console.WriteLine("..Ended");
Console.ReadKey();
}
}
class Manager
{
private static Form1 _progressForm;
public async void GoAsync()
{
var owner = new Win32Window(Process.GetCurrentProcess().MainWindowHandle);
_progressForm = new Form1();
_progressForm.Show(owner);
await Go();
_progressForm.Hide();
}
private async Task<bool> Go()
{
var job = new LongJob();
job.OnProgress += job_OnProgress;
job.Spin();
return true;
}
void job_OnProgress(int percent)
{
_progressForm.UpdateProgress(percent);
}
}
class LongJob
{
public event Progressed OnProgress;
public delegate void Progressed(int percent);
public void Spin()
{
for (var i = 1; i <= 100; i++)
{
Thread.Sleep(25);
if (OnProgress != null)
{
OnProgress(i);
}
}
}
}
class Win32Window : IWin32Window
{
private readonly IntPtr _hwnd;
public Win32Window(IntPtr handle)
{
_hwnd = handle;
}
public IntPtr Handle
{
get
{
return _hwnd;
}
}
}
}
The async and await keywords do not mean "run on a background thread." I have an async/await intro on my blog that describes what they do mean. You must explicitly place CPU-bound operations on a background thread, e.g., Task.Run.
Also, the Task-based Asynchronous Pattern documentation describes the common approaches with async code, e.g., progress reporting.
class Manager
{
private static Form1 _progressForm;
public async Task GoAsync()
{
var owner = new Win32Window(Process.GetCurrentProcess().MainWindowHandle);
_progressForm = new Form1();
_progressForm.Show(owner);
var progress = new Progress<int>(value => _progressForm.UpdateProgress(value));
await Go(progress);
_progressForm.Hide();
}
private Task<bool> Go(IProgress<int> progress)
{
return Task.Run(() =>
{
var job = new LongJob();
job.Spin(progress);
return true;
});
}
}
class LongJob
{
public void Spin(IProgress<int> progress)
{
for (var i = 1; i <= 100; i++)
{
Thread.Sleep(25);
if (progress != null)
{
progress.Report(i);
}
}
}
}
Note that the Progress<T> type properly handles thread marshaling, so there's no need for marshaling within Form1.UpdateProgress.
#StephenCleary's answer is correct. Though, I had to make a little modification to his answer to get the behavior what I think OP wants.
public void GoAsync() //no longer async as it blocks on Appication.Run
{
var owner = new Win32Window(Process.GetCurrentProcess().MainWindowHandle);
_progressForm = new Form1();
var progress = new Progress<int>(value => _progressForm.UpdateProgress(value));
_progressForm.Activated += async (sender, args) =>
{
await Go(progress);
_progressForm.Close();
};
Application.Run(_progressForm);
}
private async void button1_Click(object sender, EventArgs e)
{
IProgress<int> progress = new Progress<int>(value => { progressBar1.Value = value; });
await Task.Run(() =>
{
for (int i = 0; i <= 100; i++)
progress.Report(i);
});
}
Correct me if I'm wrong, but this seems to be the easiest way to update a progress bar.