I have a class that handles some realtime action in a thread that it starts. There are other theads in play in this application as it is very complex. When This rt action starts i need to pop up a window and close it when it is done. Sounds easy.
There are events that I hook to when this action starts and stops. In those event handlers I place the code:
private void Voice_SpeakStarted(object sender, TMSpeakStartedEventArgs e)
{
InfoWindow = new Form();
InfoWindow.Show();
}
/// <summary>
/// this is the event handler speaking stops
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void Voice_SpeakCompleted(object sender, TMSpeakCompletedEventArgs e)
{
if (InfoWindow.InvokeRequired)
{
InfoWindow.Invoke(new Action(() =>
{
InfoWindow.Close();
}));
InfoWindow.Hide();
}
}
There are times I get an error that the thread has terminated. (An error occurred invoking the method. The destination thread no longer exists.)
I always seem to get the window to show. I can not seem to get the window to close.
I also see that sometime the handler themselves do not get called.
I need help bad. I can post more code if it would be helpful.
Edited - added more code
This is how I start the class
public void start()
{
//It's already alive, nothing to do
if (alive) return;
//Make sure this is the only place where alive is set to true
alive = true;
Voice.SpeakCompleted += new Speech.TMSpeakCompletedDelegate(Voice_SpeakCompleted);
Voice.SpeakStarted += new Speech.TMSpeakStartedDelegate(Voice_SpeakStarted);
dispatch = new Thread(new ThreadStart(ProcessSayList));
dispatch.Start();
}
The constructor of the class is
public AnimationControl(dynamic parent)
{
Parent = parent;
Voice = new Speech();
q = Queue.Synchronized(new Queue(1000));
start();
}
You should really specialize your thread and stop calling code managed by other thread form any thread. Use message queues to communicate actions to your thread. This is the safest way to do multi-threading.
Example in pseudo-code:
Thread1
{
while (1)
{
read my last message in my queue;
do something according to this message like:
openwindow();
or closewindow();
}
}
Thread2
{
My life is short, I just need to post a message to thread1
}
Thread3
{
etc.
}
There are ready-to-use structures for such a thing on every system. And by doing so, it will be much more easy to understand what's happening in case of problem like that. Of course, if you don't take care, your threaded program can become absolutely linear; the goal is to make sure some parts of actions can be made in parallel and do not create a chain of threads waiting each other, one by one :)
Check my answer here for some information on the thread terminated error, and UI threading in general: understanding InvalidAsynchronousStateException occurrences
Well for one thing you're calling Hide on your window on the wrong thread even if InvokeRequired returns true.
I can also guess that you're creating your Voice instance on a new thread and returning when you get a "close" message, thus sometimes killing the thread you're trying to route windows messages through. Consider holding on to the thread until your window is actually closed.
And yes, you should post more code, there isn't a single line of code that shows how you create/dispose of that thread.
Related
As part of my App's startup procedure, it checks data integrity, and if it finds a problem it pops up a message to the user telling them that it might take a while to repair things.
I'm showing the message using MessageBox.Show. Because the data check is done from a worker thread, I'm switching over to the UI thread to make that call, and then setting a ManualResetEvent to tell the worker thread when the user has acknowledged the message.
I kick off the data check/load very early in the app's lifecycle from the constructor in the main Application class, by spinning off a worker thread (using the ThreadPool).
When I run with the debugger, and the message is displayed, the app just waits for input. When I run without the debugger, the app terminates after displaying the dialog for 10 seconds.
That 10 seconds is a big clue - it tells me that the OS thinks the app took too long to initialize (the OS kills apps that take too long to start up).
I think that my MessageBox.Show is blocking the UI thread before the App.RootFrameNavigating has a chance to be invoked.
My questions:
Does my diagnosis sound right?
I'd prefer to kick off my data load early, because it is almost entirely IO, except for this Message Box, and the sooner I can get my Model loaded, the better, but do you normally delay your data load until later in the app lifecycle?
Any other ideas/suggestions? I can't guarantee which page will be the start page, because the app could be resuming to any page. I'm also thinking of having the MessageBox.Show delay itself until the app has initialized, perhaps polling away for a flag set by App.RootFrameNavigating - does that make sense?
I think your problem is a result of kicking off the worker thread in the Application constructor. You should use the appropriate life-cycle event, in this case: PhoneApplicationService.Activated Event
So, the solution I've come up with is to still kick off the data load in a worker-thread from the Application's constructor, but in my PhoneService's class ShowDialog method that I invoke to invoke MessageBox.Show, I check to see if the initial navigation has occurred:
private readonly ManualResetEvent _appInitialized = new ManualResetEvent(false);
public void AppInitialized()
{
_appInitialized.Set();
}
public void ShowDialog(string caption, string text, Action<MessageBoxResult> callback, MessageBoxButton button = MessageBoxButton.OKCancel)
{
_appInitialized.WaitOne();
DispatcherHelper.CheckBeginInvokeOnUI(() =>
{
var result = MessageBox.Show(text, caption, button);
if (callback != null)
{
callback(result);
}
});
}
Then in my Application class:
private bool _firstNavigate = true;
private void RootFrameNavigating(object sender, NavigatingCancelEventArgs e)
{
if (_firstNavigate)
{
_firstNavigate = false;
var navigationService = (NavigationService) sender;
navigationService.Navigated += NavigationServiceNavigated;
}
....
private void NavigationServiceNavigated(object sender, NavigationEventArgs e)
{
var navigationService = (NavigationService)sender;
navigationService.Navigated -= NavigationServiceNavigated;
PhoneServices.Current.AppInitialized();
}
Anyone see any issues with this approach? Anyone come up with a better way?
Could someone shed some light on an issue I'm having?
I'm working on a wpf project. The scenario is as below:
I need to pop up a window(model window) on main UI thread and then close it. These works are started from another UI thread (to deter user from clicking on the main UI window.) then I close this window. The main code are displayed below. And it works.
As far as I know the close method would not get excuted before ShowDialog() returns (at least this is the case on UI thread, I mean code without dispatcher), does anyone have experience with multithread?
Window window;
private void Button_Click(object sender, RoutedEventArgs e)
{
Thread thread = new Thread(() =>
{
//create a window and let user work from this thread
//code is omitted.
//create another window on main UI thread
Application.Current.Dispatcher.BeginInvoke(new Action(() =>
{
window = new Window();
window.ShowDialog();
}));
//do some work here
Thread.Sleep(1000);
Application.Current.Dispatcher.BeginInvoke(new Action(() =>
{
//Thread.Sleep(1000);
window.Close();
}));
});
thread.Start();
}
Thank you for your time!
So if I understand your question correctly, you're saying that this code works exactly the way you want, but you're just trying to understand how (and why) it works?
Here's how it works. First, your thread runs this code:
Application.Current.Dispatcher.BeginInvoke(new Action(() =>
{
window = new Window();
window.ShowDialog();
}));
That queues your action on the main (UI) thread's dispatcher queue, and then returns immediately: your worker thread continues running.
When the Application first started up (typically via the compiler-generated code that initializes your App.xaml object, though you can also do it explicitly by calling Application.Run), it started its message loop, which goes something like this (pseudocode, very very simplified):
public class Application {
public void Run() {
while (!Exited && action = Dispatcher.DequeueAction())
action();
}
}
So at some point shortly after you queue the action, the UI thread will get around to pulling your action off the queue and running it, at which point your action creates a window and shows it modally.
The modal window now starts its own message loop, which goes something like this (again, very simplified):
public class Window {
public bool? ShowDialog() {
DisableOtherWindowsAndShow();
while (!IsClosed && action = Dispatcher.DequeueAction())
action();
EnableOtherWindowsAndHide();
return DialogResult;
}
}
Later, your worker thread runs this code:
Application.Current.Dispatcher.BeginInvoke(new Action(() =>
{
window.Close();
}));
Again, your action is queued to the UI thread's dispatcher queue, and then the BeginInvoke call returns immediately and your worker thread continues running.
So sooner or later, the UI thread's message loop will get around to dequeuing and executing your action, which tells the window to close. This has essentially the same effect as the user clicking the title bar's "X" button, which of course is perfectly OK to do even when you're inside a modal dialog. This causes ShowDialog's message loop to terminate (because the window is now closed), at which point the dialog is hidden and the other windows are re-enabled, ShowDialog returns, your original (ShowDialog) action is complete and so returns, and control falls back to the original message loop in Application.Run.
Note that there's one dispatcher queue per thread, not one per message loop. So your "close" action goes into the same queue that your "show dialog" action did. It's a different piece of code doing the message-loop polling now (the one inside ShowDialog instead of the one inside Application.Run), but the basics of the loop are the same.
BeginInvoke is a non-blocking method; it adds the action to the dispatcher queue, and doesn't wait for its completion. You should use Invoke instead, which calls the method synchronously on the dispatcher thread.
First of all its not a splash-screen what i want... just to be clear... ok... lets go to the description of the problem:
i have a form that fire N number of threads (i dont know how many, the user must choose)... each thread has a object, and during several moments the objects may fire a event to signal some change... there must be a form for each thread to "report" the messages that the events are sending...
my problem is: the threads create the forms perfectally... but the desappear... out of nowhere... they appear on the screen... and vanish... poof.... gone! how can i avoid that undesired "disposing"?!?!
Your threads must either
use proper InvokeRequired + Invoke logic
or run their own MessagePump (Application.Run)
Which one did you (not) do?
If you create a form in a thread, the form will vanish when the thread is done. If you want the form to survive longer than that you need to either keep the thread alive, or create the form on the application's main thread. The latter would be preferable. Just make sure that each to hook up event listener for the object in the corresponding form, and use Invoke or BeginInvoke as needed when updating the form.
A simple example:
First a worker:
class Worker
{
public event EventHandler SomethingHappened;
protected void OnSomethingHappened(EventArgs e)
{
var evnt = SomethingHappened;
if (evnt != null)
{
evnt(this, e);
}
}
public void Work()
{
// do lots of work, occasionally calling
// OnSomethingHappened
}
}
Then, in a form we have an event handler for the SomethingHappened event:
public void SomethingHappenedHandler(object sender, EventArgs e)
{
if (this.InvokeRequired)
{
this.Invoke(new Action(() => SomethingHappenedHandler(sender, e)));
return;
}
// update gui here
}
Then it's really just a matter of wiring it all together:
Worker w = new Worker();
ProgressForm f = new ProgressForm;
w.SomethingHappened += f.SomethingHappenedHandler;
f.Show();
Thread t = new Thread(w.Work);
t.Start();
Disclaimer: this sample is quickly tossed together and somewhat untested (sitting on the train, about to get off ;) ).
A Form must be hosted on a thread with a message loop. You can create a message loop by either calling Application.Run or Form.ShowDialog. However, unless you have really good reason for doing so I would avoid having more than one thread with a windows message loop.
I would also avoid creating N threads. There are better ways to parallelize N operations other than creating one thread per operation. To name only two: 1) queue a work item in the ThreadPool or 2) use the Task Parallel Library via the Task class. The problem with creating N threads is that each thread consumes a certain amount of resources. More threads means more resources will be consumed and more context switching will occur. More is not always better in the world of multithreading.
I have a windows form on the main thread and another thread that does some calculations. I'd like to update the status bar on my form from the work being done in the other thread. What's the best way to do this?
So far everything I've tried just makes things run really slowly. I'm using Visual Studio 2005.
You can use the marshaling techniques like Control.Invoke to execute a delegate on the UI thread where UI elements can be safely manipulated, but that approach is not very good. Actually, it is a terrible approach if all you want to do is update simple progress information.
By far the best method for doing this is:
Have your worker thread publish progress information to a shared variable.
Have your UI thread poll for it via a System.Windows.Forms.Timers on an interval that works well for you.
Here is what it might look like.
public class Example : Form
{
private volatile int percentComplete = 0;
private void StartThreadButton_Click(object sender, EventArgs args)
{
StatusBarUpdateTimer.Enabled = true;
new Thread(
() =>
{
for (int i = 1; i <= 100; i++)
{
DoSomeWork();
percentComplete = i;
}
}).Start();
}
private void StatusBarUpdateTimer_Tick(object sender, EventArgs args)
{
yourStatusBarPanel.Text = percentComplete.ToString() + "%";
StatusBarUpdateTimer.Enabled = percentComplete < 100;
}
}
This works well because:
The percentComplete field is declared 'volatile' ensuring its value can be reliably read from multiple threads.
The UI thread gets to dictate when and how often the UI gets updated...the way it should be!
The worker thread does not have to wait for a response from the UI thread before it can proceed as would be the case with Invoke.
It breaks the tight coupling between the UI and worker threads that Invoke would impose.
It is more efficient...considerably.
You get more throughput on both the UI and worker threads.
There is no chance of saturating the UI message queue as could be the case with BeginInvoke.
You do not have to litter you code with Invoke calls everytime you need to update the UI from the worker thread.
Make sure that you only update the user interface from the main thread or else you will have problems. You can switch your thread context by calling Invoke. There's a good post here on that.
You can send messages to the main thread and get it to update the progress bar, although you then need to check for the messages. You could also do the same sort of thing as a polling function.
What is the best way to update a label on a Windows Forms application while processing?
I have a loop that does some processing to files on the user's system when the user clicks a button.
foreach (System.IO.FileInfo f in dir.GetFiles("*.txt"))
{
// Do processing
// Show progress bar
// Update Label on Form, "f.Name is done processing, now processing..."
}
What would be some sample code?
What exactly is this called? Is it threading or delegates?
A quick fix for you would be:
Label1.Text = f.Name + " is done processing, now processing...";
Label1.Refresh();
You really want to avoid DoEvents, otherwise you'll have problems if your user repeatedly presses buttons on your form.
You should be doing this on another thread, and then updating your UI thread from that thread. You are blocking further processing by performing this work on the UI thread.
If you can't move this code to the UI thread, then you could always call Application.DoEvents, but I strongly suggest you explore these options first:
System.ComponentModel.BackgroundWorker
System.Threading.ThreadPool
System.Threading.Thread
System.Threading.Tasks namespace
You'll need to get your data from one thread to the other. This can be done in a couple of ways...
First, your "background" thread could update some kind of "CurrentStatus" string variable that it changes as it goes along. You could then put a timer on your form that would then grab the CurrentStatus variable and update the label with it.
Second, you could simply invoke the operation from the background thread to the UI thread with a delegate using the InvokeRequired property of the label control. So for example...
private delegate void UpdateStatusDelegate(string status);
private void UpdateStatus(string status)
{
if (this.label1.InvokeRequired)
{
this.Invoke(new UpdateStatusDelegate(this.UpdateStatus), new object[] { status });
return;
}
this.label1.Text = status;
}
You can call that UpdateStatus() method from any thread (UI or background), and it will detect whether or not it needs to invoke the operation on the main UI thread (and if so, does it).
To actually set up the thread, you can do so like this:
private void StartProcessing()
{
System.Threading.Thread procThread = new System.Threading.Thread(this.Process);
procThread.Start();
}
private void Process() // This is the actual method of the thread
{
foreach (System.IO.FileInfo f in dir.GetFiles("*.txt"))
{
// Do processing
// Show progress bar
// Update Label on Form, "f.Name is done processing, now processing..."
UpdateStatus("Processing " + f.Name + "...");
}
}
Then when the user clicks the "GO" button you'll simply call StartProcessing().
If your processing is lengthy do it in a backgroundworker thread.
http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.aspx
I also recommend to use :
Application.DoEvents();
Processes all Windows messages currently in the message queue.