Why is Application.Restart() not reliable?

There could be a lot of reasons for this. It's not that the method doesn't work; rather, many times programmers forget that they've put something in their code that would stop the application from automatically shutting down, or starting up. Two examples:

• The Closing event on a form can stop an app's shutdown
• If you're doing checking for an already-running process, the old one may not be closing fast enough to allow the new one to start up.

Check your code for gotchas like that. If you're seeing this behaviour within a blank application, then that's more likely to be a problem with the actual function than your code.

Check Microsoft's sourcecode of application restart.

The only time I've run into this kind of issue is when in my main form I had a custom FormClosing event handler, that performed logic and canceled the event.

EDIT:

I have now run into another instance and based on your comments it possibly mirrors what you were experiencing.

When running a single instance application, using a Mutex, I was calling Application.Restart() from a fairly embedded location, that had a lot of cleanup to do. So it seems the restart was launching a new instance before the previous instance was complete, so the Mutex was keeping the new instance from starting.

Try locking before dumping. Here's how I initiate a full app-dump. Might work for you, might not.

Context.Application.Lock();
Context.Session.Abandon();
Context.Application.RemoveAll();
Context.Application.Restart();
Context.Application.UnLock();

I Tried with below code and it is working fine

static class Program
{
    static Mutex _mutex = new Mutex(false, "MYAPP");

    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        if (!_mutex.WaitOne(1000, false))
        {
            MessageBox.Show("Another instance is already running!!!", "Already Running", MessageBoxButtons.OK,
                MessageBoxIcon.Error);
            return;
        }

        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new PrimaryForm());

        _mutex.ReleaseMutex();
    }
}

//the place where i am calling application restart used this code

Application.Restart();
Application.ExitThread();

Reference Link
https://www.codeproject.com/articles/25674/preventing-multiple-application-instances-when-usi

I have this very same issue with .Net 4.7 framework. The accepted answer was key for my success. I did had code in the FormClosing event that was taking some time and stopping the restart process. What I did was to put a sentinel like this:

If JustCloseIT = False Then
   'all closing code, like logging the session log-out to a database and all those goodies we all do.
 End If

only then the Application.Restart() worked!