Develop Reference

Crash from Invoke when MainForm is Disposed in FormClosing

I have an issue that relates to threading, cleaning up unmanaged resources and shutting down my app.
In the main UI thread I have a method that creates a new instance of class Worker. In Worker's constructor I start a new thread that has a while(Scanning) loop that updates some controls in my UI using Invoke() continuously (until Scanning bool is set to false). In the UI thread I raise the event FormClosing() whenever the application is closing down (through X button or Application.Exit() etc.). In FormClosing() I set Scanning to false and do some cleanup of unmanaged resources (that can only be done after the worker thread is done, because it uses those resources. The problem is that when I close the app down the MainForm apparently gets instantly disposed, so the app crashes at the Invoke (because it is trying to make a delegate run from UI thread, but that thread is disposed).
In an attempt to make the worker finish before the UI closes I tried to create a method StopWorker() in the worker class where I put Scanning = false, and then Thread.Join. As you can imagine the Join caused a deadlock as it makes the UI thread sleep but the Invoke needs the UI thread to move on.
In summary I need to cleanup unmanaged resources in FormClosing. I need the worker thread to be done before I do that though, as it uses these resources. The worker thread cannot finish (it uses Invoke) if the MainForm is disposed, therefore creating a tricky situation.

Based on Hans Passant's answer here, I created the below solution. It seems to be working very well.
In UI class/thread:
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
var button = sender as Button;
if (button != null && string.Equals(button.Name, #"CloseButton"))
{
//FormClosing event raised by a user-created button action
}
else
{
//FormClosing event raised by program or the X in top right corner
//Do cleanup work (stop threads and clean up unmanaged resources)
if (_bw.Scanning)
{
_bw.Scanning = false;
ClosePending = true;
e.Cancel = true;
return;
}
//Code to clean up unmanaged resources goes here (dummy code below)
ApplicationLogger.Get.Log("Doing final cleanup work and exiting application...");
MemoryHandler.Get.Dispose();
ApplicationLogger.Get.Dispose();
}
}
My worker thread is in another class that has a public bool property called Scanning. It also has this while loop (notice the line at the bottom):
private void Worker()
{
while (Scanning)
{
Thread.Sleep(50);
_sendBackValue[0] = "lbOne";
_sendBackValue[1] = "blaBla";
_synch.Invoke(_valueDelegate, _sendBackValue);
_sendBackValue[0] = "lbTwo";
_sendBackValue[1] = "blaBla";
_synch.Invoke(_valueDelegate, _sendBackValue);
_sendBackValue[0] = "lbThree";
_sendBackValue[1] = "blaBla";
_synch.Invoke(_valueDelegate, _sendBackValue);
}
MainForm.Get.Invoke((Action)(() => MainForm.Get.StopScanning()));
}
Finally, back in the UI class/thread I have this method:
public void StopScanning()
{
if (!ClosePending) return;
ApplicationLogger.Get.Log("Worker thread is closing the application...");
Close();
}

Could you not better use the BackgroundWorker class/control? It is much easier to use because it has already a lot of synchronization stuff in it.
But if you have a separate thread, in your FormClosing event, use:
yourThread.Abort();
yourThread.Join(); // or yourThread.Join(1000); where 1000 is some kind of time out value
in your thread use try-excpet-finally construct
try
{
// do your stuff
}
catch (ThreadAbortException)
{
// do someting when your thread is aborted
}
finally
{
// do the clean up. Don't let it take too long.
}
Note that the Join command will block further execution until the thread has stopped. Therefore, I would recommend a not too high value for the time out parameter, otherwise the user interface will be blocked and will irritate users.

Disclaimer: I do not advocate the use of Thread, ManualResetEvent and, above all, volatile in the .NET 4.5+ era, but since the .NET version was not specified I've done my best to address the problem while keeping things as backwards-compatible as possible.
Here's a solution which uses a polling variable and a ManualResetEvent to block the execution of the FormClosing handler until the loop has completed - without any deadlocks. In your scenario if you have a class-level reference to the Thread which runs the loop, you can use Thread.Join instead of ManualResetEvent.WaitOne in the FormClosing handler - the semantics will be the same.
using System;
using System.Threading;
using System.Windows.Forms;
namespace FormClosingExample
{
public partial class Form1 : Form
{
private volatile bool Scanning = true;
private readonly ManualResetEvent LoopFinishedMre = new ManualResetEvent(false);
private readonly SynchronizationContext UiContext;
public Form1()
{
this.InitializeComponent();
// Capture UI context.
this.UiContext = SynchronizationContext.Current;
// Spin up the worker thread.
new Thread(this.Loop).Start();
}
private void Loop()
{
int i = 0;
while (this.Scanning)
{
// Some operation on unmanaged resource.
i++;
// Asynchronous UI-bound action (progress reporting).
// We can't use Send here because it will deadlock if
// the call to WaitOne sneaks in between the Scanning
// check and sync context dispatch.
this.UiContext.Post(_ =>
{
// Note that it is possible that this will
// execute *after* Scanning is set to false
// (read: when the form has already closed),
// in which case the control *might* have
// already been disposed.
if (this.Scanning)
{
this.Text = i.ToString();
}
}, null);
// Artifical delay.
Thread.Sleep(1000);
}
// Tell the FormClosing handler that the
// loop has finished and it is safe to
// dispose of the unmanaged resource.
this.LoopFinishedMre.Set();
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
// Tell the worker that it needs
// to break out of the loop.
this.Scanning = false;
// Block UI thread until Loop() has finished.
this.LoopFinishedMre.WaitOne();
// The loop has finished. It is safe to do cleanup.
MessageBox.Show("It is now safe to dispose of the unmanaged resource.");
}
}
}
Now, while this solution is (somewhat) tailored to your description of the problem (which I interpreted to the best of my ability), I had to make a large number of assumptions. If you want a better answer, you'll need to post a concise repro of the problem - not necessarily your production code, but at least a trimmed down working version which still has all the main nuts and bolts in place and exhibits the problem you've described.

C# controlling threads (resume/suspend)

I'm trying to simulate (very basic & simple) OS process manager subsystem, I have three "processes" (workers) writing something to console (this is an example):
public class Message
{
public Message() { }
public void Show()
{
while (true)
{
Console.WriteLine("Something");
Thread.Sleep(100);
}
}
}
Each worker is supposed to be run on a different thread. That's how I do it now:
I have a Process class which constructor takes Action delegate and starts a thread from it and suspends it.
public class Process
{
Thread thrd;
Action act;
public Process(Action act)
{
this.act = act;
thrd = new Thread(new ThreadStart(this.act));
thrd.Start();
thrd.Suspend();
}
public void Suspend()
{
thrd.Suspend();
}
public void Resume()
{
thrd.Resume();
}
}
In that state it waits before my scheduler resumes it, gives it a time slice to run, then suspends it again.
public void Scheduler()
{
while (true)
{
//ProcessQueue is just FIFO queue for processes
//MainQueue is FIFO queue for ProcessQueue's
ProcessQueue currentQueue = mainQueue.Dequeue();
int count = currentQueue.Count;
if (currentQueue.Count > 0)
{
while (count > 0)
{
Process currentProcess = currentQueue.GetNext();
currentProcess.Resume();
//this is the time slice given to the process
Thread.Sleep(1000);
currentProcess.Suspend();
Console.WriteLine();
currentQueue.Add(currentProcess);
count--;
}
}
mainQueue.Enqueue(currentQueue);
}
}
The problem is that it doesn't work consistently. It even doesn't work at all in this state, i have to add Thread.Sleep() before WriteLine in Show() method of the worker, like this.
public void Show()
{
while (true)
{
Thread.Sleep(100); //Without this line code doesn't work
Console.WriteLine("Something");
Thread.Sleep(100);
}
}
I've been trying to use ManualResetEvent instead of suspend/resume, it works, but since that event is shared, all threads relying on it wake up simultaneously, while I need only one specific thread to be active at one time.
If some could help me figure out how to pause/resume task/thread normally, that'd be great.
What I'm doing is trying to simulate simple preemptive multitasking.
Thanks.

Thread.Suspend is evil. It is about as evil as Thread.Abort. Almost no code is safe in the presence of being paused at arbitrary, unpredictable locations. It might hold a lock that causes other threads to pause as well. You quickly run into deadlocks or unpredictable stalls in other parts of the system.
Imagine you were accidentally pausing the static constructor of string. Now all code that wants to use a string is halted as well. Regex internally uses a locked cache. If you pause while this lock is taken all Regex related code might pause. These are just two egregious examples.
Probably, suspending some code deep inside the Console class is having unintended consequences.
I'm not sure what to recommend to you. This seems to be an academic exercise so thankfully this is not a production problem for you. User-mode waiting and cancellation must be cooperative in practice.

I manage to solve this problem using static class with array of ManualResetEvent's, where each process is identified by it's unique ID. But I think it's pretty dirty way to do it. I'm open to other ways of accomplishing this.
UPD: added locks to guarantee thread safety
public sealed class ControlEvent
{
private static ManualResetEvent[] control = new ManualResetEvent[100];
private static readonly object _locker = new object();
private ControlEvent() { }
public static object Locker
{
get
{
return _locker;
}
}
public static void Set(int PID)
{
control[PID].Set();
}
public static void Reset(int PID)
{
control[PID].Reset();
}
public static ManualResetEvent Init(int PID)
{
control[PID] = new ManualResetEvent(false);
return control[PID];
}
}
In worker class
public class RandomNumber
{
static Random R = new Random();
ManualResetEvent evt;
public ManualResetEvent Event
{
get
{
return evt;
}
set
{
evt = value;
}
}
public void Show()
{
while (true)
{
evt.WaitOne();
lock (ControlEvent.Locker)
{
Console.WriteLine("Random number: " + R.Next(1000));
}
Thread.Sleep(100);
}
}
}
At Process creation event
RandomNumber R = new RandomNumber();
Process proc = new Process(new Action(R.Show));
R.Event = ControlEvent.Init(proc.PID);
And, finally, in scheduler
public void Scheduler()
{
while (true)
{
ProcessQueue currentQueue = mainQueue.Dequeue();
int count = currentQueue.Count;
if (currentQueue.Count > 0)
{
while (count > 0)
{
Process currentProcess = currentQueue.GetNext();
//this wakes the thread
ControlEvent.Set(currentProcess.PID);
Thread.Sleep(quant);
//this makes it wait again
ControlEvent.Reset(currentProcess.PID);
currentQueue.Add(currentProcess);
count--;
}
}
mainQueue.Enqueue(currentQueue);
}
}

The single best advice I can give with regard to Suspend() and Resume(): Don't use it. You are doing it wrong™.
Whenever you feel a temptation to use Suspend() and Resume() pairs to control your threads, you should step back immediately and ask yourself, what you are doing here. I understand, that programmers tend to think of the execution of code paths as of something that must be controlled, like some dumb zombie worker that needs permament command and control. That's probably a function of the stuff learned about computers in school and university: Computers do only what you tell them.
Ladies & Gentlemen, here's the bad news: If you are doing it that way, this is called "micro management", and some even would call it "control freak thinking".
Instead, I would strongly encorage you to think about it in a different way. Try to think of your threads as intelligent entities, that do no harm and the only thing they want is to be fed with enough work. They just need a little guidance, that's all. You may place a container full of work just in front of them (work task queue) and have them pulling the tasks from that container themselves, as soon as the finished their previous task. When the container is empty, all tasks are processed and there's nothing left to do, they are allowed to fall asleep and WaitFor(alarm) which will be signaled whenever new tasks arrive.
So instead of command-and-controlling a herd of dumb zombie slaves that can't do anything right without you cracking the whip behind them, you deliberately guide a team of intelligent co-workers and just let it happen. That's the way a scalable architecture is built. You don't have to be a control freak, just have a little faith in your own code.
Of course, as always, there are exceptions to that rule. But there aren't that many, and I would recommend to start with the work hypothesis, that your code is probably the rule, rather than the exception.

WPF/C# Cancelling BackgroundWorker call outside DoWork

I have a BackgroundWorker DoWork function as follows
private void WorkerGetFeedData(object sender, DoWorkEventArgs args)
{
_feed.FetchUserData(_userNameCollection);
}
The FetchUserData is a function in another class(whose object is _feed) in another project in the same solution. The data fetch process takes considerable time and I'd like for the user to be able to cancel the process if necessary. How do I convey a cancel operation from the user to a function call elsewhere and just stop it?

You can use BackgroundWorker.CancelAsync method. Here's more info with example: MSDN
To be more exact to your problem, pass the worker to FetchUserData. It is the sender parameter. Then in the FetchUserData function you can check if the flag BackgroundWorker.CancellationPending is set and finish your method.
void FetchUserData(IEnumerable<Users> userNameCollection, BackgroundWorker worker)
{
// ...
if(worker.CancellationPending)
{
// Finish method..
}
}
And the WorkerGetFeedData method:
private void WorkerGetFeedData(object sender, DoWorkEventArgs args)
{
var worker = sender as BackgroundWorker;
if(worker != null)
_feed.FetchUserData(_userNameCollection, worker);
}

Send a message (event) to the worker thread that changes a boolean, indicating that the worker thread should end/cancel itself.
Edit: I was a bit quick reading your question, missing the important part. While trying to make up I found this interesting article which might help:
http://ondotnet.com/pub/a/dotnet/2003/02/18/threadabort.html
It does work when simulating a long running process with Thread.Sleep(), being at work I dont have time right now to write code to test it on a proper application/long running task.
class Program
{
static void Main(string[] args)
{
Thread thread = new Thread(new ThreadStart(Foo));
thread.Start();
Console.ReadKey();
thread.Abort(); // cause ThreadAbortException to be thrown
Console.ReadKey();
}
static void Foo()
{
try
{
while( true )
{
Console.WriteLine("Long running process...");
Thread.Sleep(100000);
}
}
catch( ThreadAbortException ex )
{
Console.WriteLine(ex.Message);
}
finally
{
Console.WriteLine("Thread Closing ...");
}
}
}
The problem with this approach is - it uses Thread.Abort() - which interrupts the thread no matter what it is doing. This can lead to left open handles, memory leaks, etc. So while it may help it would most likely be very unwise to use.
Ian Griffiths supposes that another way to (force) cancel a thread would be to run it in its own, seperate process: http://www.interact-sw.co.uk/iangblog/2004/11/12/cancellation which you can kill whenever without affecting your process's internal state.

How to respond events while a threaded operation is running in .NET

I have a class to launch background operations in a WinForms application. I need to write this background worker since my requisites are using .NET 1.1, so I cannot use BackgroundWorker, that is only available from .NET 2.0
This class get a delegate and execute it in a thread. I want the main thread to respond to events.
I also want to indicate that the operation is running setting the application cursor to Cursors.WaitCursor.
What do you think about current implementation? I'm interested in the method WaitTillThreadFinishes(), because I'm not sure about Application.DoEvents(), please read the code and share with me opinions about WaitTillThreadFinishes.
The following code executes the operation:
private object ExecuteOperation (Delegate target, params object[] parameters)
{
mTargetDelegate = target;
mTargetParameters = parameters;
mTargetThread = new Thread(new ThreadStart(ThreadProc));
mTargetThread.Name = mTargetDelegate.Method.Name;
mOperationFinished = false;
// start threaded operation
mTargetThread.Start();
// perform active waiting
WaitTillThreadFinishes();
return mTargetResult;
}
The following code is executed in a thread, simply call the delegate, and wrap exceptions:
protected virtual void ThreadProc()
{
try
{
mTargetResult = mTargetDelegate.DynamicInvoke(mTargetParameters);
}
catch (ThreadAbortException) { }
catch (Exception ex)
{
//manage exceptions here ...
}
finally
{
mOperationFinished = true;
}
}
And this is the code performs an active waiting. I'm interested on share with you. Any better option? Any pain calling Application.DoEvents() massively?
private void WaitTillThreadFinishes ()
{
// Active wait to respond to events with a WaitCursor
while (!mOperationFinished)
{
// sleep to avoid CPU usage
System.Threading.Thread.Sleep(100);
Application.DoEvents();
Cursor.Current = Cursors.WaitCursor;
}
Cursor.Current = Cursors.Default;
}
Thanks in advance.

Please let me know if i understood your question correctly.
Why dont you use an event to notify the UI that the worker finished his job?
This way, the UI doen't get blocked by the worker, and you avoid busy waiting.
Sample Implementation
public class MyBackgroundWorker
{
// Fields
private Delegate _target;
private object[] _arguments;
// Events
public event EventHandler RunWorkerStarted;
public event EventHandler<RunWorkerCompletedEventArgs> RunWorkerCompleted;
// Event Invocators
public void InvokeRunWorkerStarted()
{
var handler = RunWorkerStarted;
if (handler != null) handler(this, new EventArgs());
}
public void InvokeRunWorkerCompleted(object result)
{
var handler = RunWorkerCompleted;
if (handler != null) handler(this, new RunWorkerCompletedEventArgs(result));
}
public void RunWorkerAsync(Delegate target, params object[] arguments)
{
_target = target;
_arguments = arguments;
new Thread(DoWork).Start(arguments);
}
// Helper method to run the target delegate
private void DoWork(object obj)
{
_target.DynamicInvoke(_arguments);
// Retrieve the target delegate's result and invoke the RunWorkerCompleted event with it (for simplicity, I'm sending null)
InvokeRunWorkerCompleted(null);
}
}
internal class RunWorkerCompletedEventArgs : EventArgs
{
public RunWorkerCompletedEventArgs(object result)
{
Result = result;
}
public object Result { get; set; }
}
Usage
In the UI you can use it this way:
private void button1_Click(object sender, EventArgs e)
{
var worker = new MyBackgroundWorker();
worker.RunWorkerStarted += worker_RunWorkerStarted;
worker.RunWorkerCompleted += worker_Completed;
worker.RunWorkerAsync(new MethodInvoker(SomeLengthyOperation), null);
}
void worker_RunWorkerStarted(object sender, EventArgs e)
{
}
void worker_Completed(object sender, EventArgs e)
{
MessageBox.Show("Worker completed");
}
private void SomeLengthyOperation()
{
Thread.Sleep(5000);
}
Final Notes
Remember to Invoke() in the event handlers to access the UI thread correctly. You can also modify the worker so this is done in a safe way.

There isn't much support in 1.1 for doing this, but I'll tell you what I'd do (sorry, no code at this time).
As for the asynchronous operation, I'd use the APM to kick off and complete the asynchronous method. This is fully supported in 1.1, so no worries there.
The idea is that in the UI, you store some indication that work is being done (a boolean field, for example) and (optionally) a Timer used to "wake up" the UI on a regular basis to check on the current status of the background work and indicate this to the user.
You would set the boolean to indicate you are working in the background, call BeginInvoke() on your delegate (using the overload that takes a callback search for "Executing a Callback Method When an Asynchronous Call Completes
"), and start the Timer. When the user attempts to use the UI, you would optionally check the boolean and cancel the operation, thus preventing the user from doing something harmful while you are waiting. When the timer Ticks, you can check the status of your asynchronous method by, say, a shared field that the method writes updates to and the UI reads. For example, a double which the UI uses to update a progress bar.
Once the callback fires, you clean up your asynchronous mess (i.e., call EndInvoke, and handle any exceptions thrown, etc), turn off the Timer and reset your boolean running indication field.
By using this method, you can keep the UI completely responsive (and partially usable, depending on your overall design), can set up a mechanism to abort the background worker (through the use of another field, the reverse of the boolean mentioned earlier, and inform the user of the status of the operation.

There is occasionally a case for kicking off a thread and waiting for its return, if you are doing other things in the meantime, but in this case, with the code you have shown, it is meaningless.
If you want the threadProc to allow for events to be processed, then call doevents in that, which will free up the CPU briefly, allowing for processing.
Unless you have a particular reason for needing to thread processes, you should not do it. Getting it right - as Ian Boyd has said - is difficult, and the more you need to interact with it the harder it is. If you can run fire-and-forget threads, that is the easiest.

Ideally you start the asynchronous operation and leave your form alone (aside from maybe using the Cursors.AppStarting cursor).
When your threaded operation completes, it then needs to fire some sort of BackgroundOperationComplete event. This is where your would call from your asynchronous delegate code:
form.Invoke(BackgroundOperationComplete);
The form's BackgroundOperationComplete method is where you can handle the fact that the background operation is complete:
void BackgroundOperationComplete()
{
this.Cursor = Cursors.DefaultCursor;
lblAnswer.Text = "The thread is done";
}
If all else fails, keep the operation synchronous, and use an IProgressDialog. (brief conceptual pseudo-code from memory):
void DoStuff()
{
IProgressDialog pd = new ProgressDialog();
pd.SetTitle = "Calculating Widgets";
pd.StartTimer(PDTIMER_RESET, NULL)
pd.StartProgressDialog(this.Handle, NULL, PROGDLG_MODAL | PROGDLG_NOTIME | PROGDLG_NOPROGRESSBAR | PROGDLG_NOCANCEL, NULL);
try
{
pd.SetLine(1, "Please wait while the widgets are frobbed");
DoTheThingThatDoesTheSynchronousStuff();
}
finally
{
pd.StopProgressDialog();
}
pd = null;
}

UI Thread .Invoke() causing handle leak?

In what circumstances would updating a UI control from a non-UI thread could cause the processes' handles to continually increase, when using a delegate and .InvokeRequired?
For example:
public delegate void DelegateUIUpdate();
private void UIUpdate()
{
if (someControl.InvokeRequired)
{
someControl.Invoke(new DelegateUIUpdate(UIUpdate));
return;
}
// do something with someControl
}
When this is called in a loop or on timer intervals, the handles for the program consistently increase.
EDIT:
If the above is commented out and amended as such:
public delegate void DelegateUIUpdate();
private void UIUpdate()
{
//if (someControl.InvokeRequired)
//{
// someControl.Invoke(new DelegateUIUpdate(UIUpdate));
// return;
//}
CheckForIllegalCrossThreadCalls = false;
// do something with someControl
}
...then the handles stop incrementing, however I don't want to allow cross thread calls, of course.
EDIT 2:
Here is a sample that shows the handles increase:
Thread thread;
private delegate void UpdateGUI();
bool UpdateTheGui = false;
public Form1()
{
InitializeComponent();
thread = new Thread(new ThreadStart(MyThreadLoop));
thread.Start();
}
private void MyThreadLoop()
{
while (true)
{
Thread.Sleep(500);
if (UpdateTheGui)
{
UpdateTheGui = false;
UpdateTheGuiNow();
}
}
}
private void UpdateTheGuiNow()
{
if (label1.InvokeRequired)
{
label1.Invoke(new UpdateGUI(UpdateTheGuiNow));
return;
}
label1.Text = DateTime.Now.ToString("MM-dd-yyyy HH:mm:ss");
label2.Text = DateTime.Now.ToString("MM-dd-yyyy HH:mm:ss");
label3.Text = DateTime.Now.ToString("MM-dd-yyyy HH:mm:ss");
}
private void btnInvoke_Click(object sender, EventArgs e)
{
UpdateTheGui = true;
}

I had the same problem with
this.Invoke(new DelegateClockUpdate(ChangeClock), sender, e);
creating one handle each call.
The handle increments because Invoke is Synchronous and effectively the handle has been left hanging.
Either a Wait Handle should be used to process the result or the Asynchronous BeginInvoke method as shown below.
this.BeginInvoke(new DelegateClockUpdate(ChangeClock), sender, e);

The Control.Invoke() method doesn't consume any handles. However, this code is clearly called from a thread. A Thread does consume handles, 5 of them.
The Thread class doesn't have a Dispose() method, although it ought to have one. That was probably by design, it would be very difficult to call reliably, impossibly so for threadpool threads. The 5 handles that a thread requires are released by the finalizer. Your program will require ever increasing amounts of handles if the finalizer never runs.
Not getting the finalizer to run is quite unusual. You would have to have a program that starts a lot of threads but doesn't allocate a lot of memory. This tends to only happen in static tests. You can diagnose this condition with Perfmon.exe, use the .NET memory performance counters and check if gen #0 collections are being done.
If this happens in a production program then you'll have to call GC.Collect() yourself to avoid a runaway handle leak.

I've seen the same thing in my code. I fixed it by replacing Invoke with BeginInvoke. The handle leak went away.
Doron.

I actually see the same problem occuring as JYelton. I have the same call from within a thread to update the UI.
As soon as the line someControl.Invoke(new DelegateUIUpdate(UIUpdate)); is called, the handle increases by one. There is certainly a leak of some kind on the invoke, but I have no idea what is causing it. This has been verified on several systems.

Aync call with explicit handle finalize. Exapmle:
public static class ActionExtensions
{
private static readonly ILog log = LogManager.GetLogger(typeof(ActionExtensions));
/// <summary>
/// Async exec action.
/// </summary>
/// <param name="action">Action.</param>
public static void AsyncInvokeHandlers(
this Action action)
{
if (action == null)
{
return;
}
foreach (Action handler in action.GetInvocationList())
{
// Initiate the asychronous call. Include an AsyncCallback
// delegate representing the callback method, and the data
// needed to call EndInvoke.
handler.BeginInvoke(
ar =>
{
try
{
// Retrieve the delegate.
var handlerToFinalize = (Action)ar.AsyncState;
// Call EndInvoke to free resources.
handlerToFinalize.EndInvoke(ar);
var handle = ar.AsyncWaitHandle;
if (handle.SafeWaitHandle != null && !handle.SafeWaitHandle.IsInvalid && !handle.SafeWaitHandle.IsClosed)
{
((IDisposable)handle).Dispose();
}
}
catch (Exception exception)
{
log.Error("Async Action exec error.", exception);
}
},
handler);
}
}
}
See http://msdn.microsoft.com/en-us/library/system.iasyncresult.asyncwaithandle.aspx note:
When you use the BeginInvoke method of a delegate to call a method asynchronously and obtain a wait handle from the resulting IAsyncResult, we recommend that you close the wait handle as soon as you are finished using it, by calling the WaitHandle.Close method. If you simply release all references to the wait handle, system resources are freed when garbage collection reclaims the wait handle, but garbage collection works more efficiently when disposable objects are explicitly closed or disposed. For more information, see the AsyncResult.AsyncWaitHandle property.

Here's an extension method which functions similarly to the normal Invoke call, but will clean up the handle after:
namespace ExtensionMethods
{
public static class ExtensionMethods
{
public static void InvokeAndClose(this Control self, MethodInvoker func)
{
IAsyncResult result = self.BeginInvoke(func);
self.EndInvoke(result);
result.AsyncWaitHandle.Close();
}
}
}
You can then call it very similarly to a normal invoke:
myForm.InvokeAndClose((MethodInvoker)delegate
{
someControl.Text = "New Value";
});
It will block and wait for the delegate to execute, then close the handle before returning.

This is the standard pattern for using Invoke to marshall updates to the UI thread.
Are you sure your problem is not being caused by other code in your application that is not included in your question?

I don't think it is related. Perhaps just waiting for the garbage collector to dispose the newly allocated object(s) inside Invoke().