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Asked: 2026-06-18T07:39:26+00:00

I have this code: private void timer1_Tick(object sender, EventArgs e) { MessageBox.Show(Thread.CurrentThread.ManagedThreadId.ToString()); } the

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I have this code:

    private void timer1_Tick(object sender, EventArgs e)
    {
        MessageBox.Show(Thread.CurrentThread.ManagedThreadId.ToString());
    }

the timer is enabled, with interval = 100.

This result in an infinite number of message boxes to appear over each other, when I was expecting them to simply BLOCK the next event until the current messagebox is closed.

In more complicated applications this could lead to unpreditable results, and its as if more than 1 thread have access to the same function, but actually it is the same thread.

Why is this happening ?

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1 Answer

  1. Editorial Team

    The message box is a modal dialog which pumps the message queue. And so that allows for the timer tick messages to fire, since they are posted to the GUI thread’s message queue.

    This is always the case for a modal dialog that is shown in the GUI thread. Since each thread has only one message queue, the modal dialog’s message pump will pull of the timer tick messages.

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