How do I suppress a thread.abort() error C# ?

Question

I am showing a splash screen on a background thread while my program loads. Once it loads I am aborting the Thread as it's only purpose was to show a Now Loading splash form.

My problem is that when aborting a Thread it throws a ThreadAbortException that the user can just click Continue on.

How do I deal with this? I was trying to suppress it like so -->

            try
        {
            Program.splashThread.Abort();
        }
        catch(Exception ex)
        {

        }

but I have a feeling that is going to get me yelled at here and it doesn't work any way.

Thanks!

Answer 1

Change the exception type to ThreadAbortException and add a call to ResetAbort()

    try
    {
        Program.splashThread.Abort();
    }
    catch(ThreadAbortException ex)
    {
        Thread.ResetAbort();
    }

In general, aborting threads is considered very bad practice and can lead to all sorts of hard to track down bugs. Have you considered figuring out a way to just close the splash window or use some sort of polling to stop the thread when a flag has been set?

Answer 2

Please refer to the following link obtained doing a Google search (first result returned):

http://msdn.microsoft.com/en-us/library/5b50fdsz.aspx

Pay special attention to this part:

When this method is invoked on a thread, the system throws a ThreadAbortException in the thread to abort it. ThreadAbortException is a special exception that can be caught by application code, but is re-thrown at the end of the catch block unless ResetAbort is called. ResetAbort cancels the request to abort, and prevents the ThreadAbortException from terminating the thread. Unexecuted finally blocks are executed before the thread is aborted.

Answer 3

Why would you do that? Just set a flag that the thread polls, then eventually when the thread picks it up it'll close itself.

Answer 4

Using Threadabort is not recommened. It's evil. Why not use another mechanism like an (Auto/Manual)ResetEvent? Start the thread with the splash-screen, wait on the event. If the other code is done loading stuff, set the event en allow the splash-screen to close itself the normal (nice) way.

Answer 5

I think you should also look at this post as a very good explanation of canceling a thread.

Answer 6

You don't need to cancel the thread. I'll exemplify with code.

In the splash screen form:

public void CloseSplash()
{
    Invoke((MethodInvoker)delegate
    {
        this.Close();
    });
}

In the Program.cs file:

private static Splash _splash = null;
public static void CloseSplash()
{
    if (_splash!= null)
    {
        _splash.CloseSplash();
    }
}

Now, when your Main method starts, show the splash in a thread:

Thread t = new Thread(new ThreadStart(delegate
{
    _splash = new Splash();
    _splash.ShowDialog();
}));

t.Start();

...and when you want it to close, just close it:

Program.CloseSplash();

Then you don't need to worry about aborting the thread; it will exit gracefully.

Answer 7

Some points. The ThreadAbort exception IS the reason the thread aborts. It is not a side effect of you calling abort. When you call abort on a thread, the runtime forces a threadabort exception to be propagated to the thread. This exception can be caught because it allows the user to perform some cleanup before the thread aborts.

The exception is then rethrown automatically to ensure that the thread is aborted. If the exception was caught and if it was not rethrown the thread would never abort.

Really intelligent design actually.

So it is really OK to catch that exception. In fact you should. But catch only that specific exception and not the general exception. (as shown below) catch(ThreadAbortException ex) { //This is an expected exception. The thread is being aborted }

Answer 8

I've used the solution suggested by Fredrik Mörk. It's very clear and elegant. Otherwise I found a problem if we instantiate the splash form before launching the real application (application.run (mainform...)):

it raises an invalidOprationException caused by the form-handle still not exists in the calling-thread. To create the handle directly in the thread t (and skip this exception!) try to launch the splash form in this way:

Thread t = new Thread(new ThreadStart(delegate
{
    _splash = new Splash();
     Application.Run(_splash);
}));

t.Start();

and, if you plan to call the closeSplash method in more branches of the program, force the null value after the first call:

    private static Splash _splash = null;
    public static void CloseSplash()
    {
        if (_splash!= null)
        {
            _splash.CloseSplash();
            _splash=null;
        }
}