I'm testing my app with mono in prevision of a Linux port, and I have a threading problem. I initially considered pasting 3000 code lines here, but finally I've devised a small minimal example ;)
You have a form with a button (poetically named Button1, and a label (which bears, without surprise, the name Label1)). The whole lot is living a happy life on a form called Form1. Clicking Button1 launches an infinite loop that increments a local counter and updates Label1 (using Invoke) to reflect its value.
Now in Mono, if you resize the form, the label stops updating, never to restart. This doesn't happen with MS implementation. BeginInvoke doesn't work any better; worse, it makes the UI hang in both cases.
Do you know where this discrepancy comes from? How would you solve it? And finally, why doesn't BeginInvoke work here? I must be making a huge mistake... but which?
EDIT: Some progress so far:
- Calling BeginInvoke does in fact work; only, the UI just doesn't refresh fast enough, so it seems to stop.
- On mono, what happens is that the whole thread hangs when you insert a message in the UI queue (eg by resizing the form). In fact, the synchronous
Invokecall never returns. I'm trying to understand why. - Of interest: even using
BeginInvoke, the asynchronous calls don't get executed before the resizing operation ends. On MS.Net, they keep running while resizing.
The code looks like this (C# version lower):
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim T As New Threading.Thread(AddressOf Increment)
T.Start()
End Sub
Sub UpdateLabel(ByVal Text As String)
Label1.Text = Text
End Sub
Delegate Sub UpdateLabelHandler(ByVal Text As String)
Sub Increment()
Dim i As Long = 0
Dim UpdateLabelDelegate As New UpdateLabelHandler(AddressOf UpdateLabel)
Try
While True
i = (i + 1) Mod (Long.MaxValue - 1)
Me.Invoke(UpdateLabelDelegate, New Object() {i.ToString})
End While
Catch Ex As ObjectDisposedException
End Try
End Sub
End Class
Or, in C#,
public class Form1
{
private void Button1_Click(System.Object sender, System.EventArgs e)
{
System.Threading.Thread T = new System.Threading.Thread(Increment);
T.Start();
}
public void UpdateLabel(string Text)
{
Label1.Text = Text;
}
public delegate void UpdateLabelHandler(string Text);
public void Increment()
{
long i = 0;
UpdateLabelHandler UpdateLabelDelegate = new UpdateLabelHandler(UpdateLabel);
try {
while (true) {
i = (i + 1) % (long.MaxValue - 1);
this.Invoke(UpdateLabelDelegate, new object[] { i.ToString() });
}
} catch (ObjectDisposedException Ex) {
}
}
}