Performing work asynchronously in .NET 4

Question

I have legacy code which performs some very long operations on the UI thread. What I want to do is to show a progress bar with message and run the work on another thread. Unfortunately , for now I don't have access to VS2012 so I can't use the async keyword. I've written some code which works fine with operations of 0-1 parameters and no return value using Action. But when I tried adjusting it to support Func I encountered some issues with invoking the tasks and returning TResult. Attached is my original code, would appreciate any suggestions. Thanks, Omer

 public partial class FreeProgressBarFrm : System.Windows.Forms.Form { #region Members /// <summary> /// timer for the progress bar. /// </summary> private Timer m_Timer = new Timer(); /// <summary> /// Delegate for the background operation to perform. /// </summary> private Action m_backgroundOperation; /// <summary> /// Standard operation to show the user while the operation is in progress. /// </summary> private static readonly string m_performingUpdatesMessage = IO_Global.GetResourceString("Performing updates, please wait", "Performing updates, please wait", null); #endregion #region Constructor /// <summary> /// Constructor /// </summary> /// <param name="backgroundDelegate"> Delegate for the background operation to perform</param> /// <param name="operationName">meessage to show the user while the operation is in progress.</param> public FreeProgressBarFrm(Action backgroundDelegate, string operationName) { InitializeComponent(); m_backgroundOperation = backgroundDelegate; this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None; this.lblOperation.Text = operationName; m_Timer.Interval = 1000; m_Timer.Tick += new EventHandler(m_Timer_Tick); } /// <summary> /// Constructor , for progressbar with defalt user message (performing updates, please wait). /// </summary> /// <param name="backgroundDelegate"> Delegate for the background operation to perform</param> /// <param name="operationName">operation display name</param> public FreeProgressBarFrm(Action backgroundDelegate): this(backgroundDelegate, m_performingUpdatesMessage) { } #endregion #region Methods /// <summary> /// Call this method to begin backgorund operation while /// showing the progress bar to the client. /// </summary> public void Wait() { ShowDialog(ControlsHelper.MainFrm); } /// <summary> /// Advance the progress bar /// </summary> /// <param name="sender"></param> /// <param name="e"></param> private void m_Timer_Tick(object sender, EventArgs e) { PerformStep(); } /// <summary> /// Advance the progress bar /// </summary> private void PerformStep() { this.progressBar1.PerformStep(); this.lblOperation.Refresh(); if (this.progressBar1.Value == this.progressBar1.Maximum) { this.progressBar1.Value = this.progressBar1.Minimum; } } /// <summary> /// Load the form , start the progress bar and backroud task. /// </summary> /// <param name="sender"></param> /// <param name="e"></param> private void ProgressBarFrm_Load(object sender, EventArgs e) { m_Timer.Start(); this.lblOperation.Refresh(); Task task = new Task(m_backgroundOperation); Task UITask = task.ContinueWith(delegate { OnWorkCompleted(); }, TaskScheduler.FromCurrentSynchronizationContext()); try { task.Start(); } catch (Exception) { Close(); throw; } } /// <summary> /// Called when the work has been completed. /// </summary> private void OnWorkCompleted() { Close(); } /// <summary> /// Close the timer. /// </summary> /// <param name="sender"></param> /// <param name="e"></param> private void ProgressBarFrm_FormClosing(object sender, FormClosingEventArgs e) { if (m_Timer != null) { m_Timer.Dispose(); m_Timer = null; } } #endregion }

Could you give us some more information about the issues you are getting? — Matthew Watson
– Matthew Watson, Commented Feb 18, 2013 at 9:45
The only API to create task with parameter I see passes an object as the state. this is not suitable because like I've said I'm dealing with legacy code which means I want to map the Func to an existing method which probably uses and inherited type as parameter- not Object directly. — omer schleifer
– omer schleifer, Commented Feb 18, 2013 at 10:05

hackp0int · Accepted Answer · 2013-02-18 11:49:11Z

Here is the way i'm executing some async work,

public static class TaskExecuter { private static readonly ThreadLocal<List<BackgroundTask>> TasksToExecute = new ThreadLocal<List<BackgroundTask>>(() => new List<BackgroundTask>()); public static Action<Exception> ExceptionHandler { get; set; } public static void ExecuteLater(BackgroundTask task) { TasksToExecute.Value.Add(task); } public static void Discard() { TasksToExecute.Value.Clear(); } public static void StartExecuting() { var value = TasksToExecute.Value; var copy = value.ToArray(); value.Clear(); if (copy.Length > 0) { Task.Factory.StartNew(() => { foreach (var backgroundTask in copy) ExecuteTask(backgroundTask); }, TaskCreationOptions.LongRunning) .ContinueWith(task => { if (ExceptionHandler != null) ExceptionHandler(task.Exception); }, TaskContinuationOptions.OnlyOnFaulted); } } public static void ExecuteTask(BackgroundTask task) { task.Run(); } }

Here is the base class

 public abstract class BackgroundTask { protected readonly Logger Logger = LogManager.GetCurrentClassLogger(); protected virtual void Initialize() { } protected virtual void OnError(Exception e) { //do some work } public bool? Run() { Logger.Info("Started task: {0}", GetType().Name); Initialize(); try { Execute(); TaskExecuter.StartExecuting(); return true; } catch (Exception e) { Logger.ErrorException("Could not execute task " + GetType().Name, e); OnError(e); return false; } finally { TaskExecuter.Discard(); Logger.Info("Finished task: {0}", GetType().Name); } } public abstract void Execute(); }

Here is the example of using

public class SendEmailTask : BackgroundTask { private const string MailServerIp = "yourip"; public string[] To { get; set; } public string From { get; set; } public string Template { get; set; } public object ViewContext { get; set; } public string[] Attachments { get; set; } public string Subject { get; set; } public override void Execute() { MailMessage message = new MailMessage(); try { MailAddress mailAddress = new MailAddress(From); message.From = mailAddress; foreach (string to in To) message.To.Add(to); message.Subject = Subject; if (Attachments.ReturnSuccess()) { foreach (string attachment in Attachments) message.Attachments.Add(new Attachment(attachment)); } message.Priority = MailPriority.High; message.Body = Template; message.AlternateViews .Add(AlternateView .CreateAlternateViewFromString(ViewContext.ToString(), new ContentType("text/html"))); message.IsBodyHtml = true; new SmtpClient(MailServerIp) { Port = 25, UseDefaultCredentials = true }.Send(message); } catch (Exception e) { Logger.FatalException("Error sending email:", e); } finally { message.Dispose(); } } public override string ToString() { return string.Format("To: {0}, From: {1}, Template: {2}, ViewContext: {3}, Attachments: {4}, Subject: {5}", To, From, Template, ViewContext, Attachments, Subject); } }

Here i've added a changed version for your needs

public static class AsyncExecuter { private static readonly ThreadLocal<List<Action>> TasksToExecute = new ThreadLocal<List<Action>>(() => new List<BackgroundTask>()); public static Action<Exception> ExceptionHandler { get; set; } public static void ExecuteLater(BackgroundTask task) { TasksToExecute.Value.Add(task); } public static void Discard() { TasksToExecute.Value.Clear(); } public static void StartExecuting() { var value = TasksToExecute.Value; var copy = value.ToArray(); value.Clear(); if (copy.Length > 0) { Task.Factory.StartNew(() => { foreach (var backgroundTask in copy) ExecuteTask(backgroundTask); }, TaskCreationOptions.LongRunning) .ContinueWith(task => { if (ExceptionHandler != null) ExceptionHandler(task.Exception); }, TaskContinuationOptions.OnlyOnFaulted); } } public static void ExecuteTask(Action task) { task.Invoke(); } }

Thanks for your suggestion. However, I'm looking for a way to do the work asynchronously with minimum impact to the legacy code.
If you look at my example, I didn't have to change anything in the existing code. Instead of calling a method directly I passed it as an Action to the FreeProgressBar control. If I am to use your code as a reference, than for every method I will have to write an xxxTask with matching members and to invoke it instead of the method, right?
Ohhhh no you don't have to do it, Just rewrite it to match your needs, that's just an idia, like you searched for, instead of Background task just send any Func<> you like
@omerschleifer here i've added an example of task executor for your needs

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