Prevent multiple instances of a given app in .NET?

Question

In .NET, what's the best way to prevent multiple instances of an app from running at the same time? And if there's no "best" technique, what are some of the caveats to consider with each solution?

Answer 1

Be sure to consider security when restricting an application to a single instance:

Full article: https://blogs.msdn.microsoft.com/oldnewthing/20060620-13/?p=30813

We are using a named mutex with a fixed name in order to detect whether another copy of the program is running. But that also means an attacker can create the mutex first, thereby preventing our program from running at all! How can I prevent this type of denial of service attack?

...

If the attacker is running in the same security context as your program is (or would be) running in, then there is nothing you can do. Whatever "secret handshake" you come up with to determine whether another copy of your program is running, the attacker can mimic it. Since it is running in the correct security context, it can do anything that the "real" program can do.

...

Clearly you can't protect yourself from an attacker running at the same security privilege, but you can still protect yourself against unprivileged attackers running at other security privileges.

Try setting a DACL on your mutex, here's the .NET way: https://msdn.microsoft.com/en-us/library/system.security.accesscontrol.mutexsecurity(v=vs.110).aspx

Answer 2

http://www.codeproject.com/KB/cs/SingleInstancingWithIpc.aspx

Answer 3

Use VB.NET! No: really ;)

using Microsoft.VisualBasic.ApplicationServices;

The WindowsFormsApplicationBase from VB.Net provides you with a "SingleInstace" Property, which determines other Instances and let only one Instance run.

Answer 4

You have to use System.Diagnostics.Process.

Check out: http://www.devx.com/tips/Tip/20044

Answer 5

After trying multiple solutions i the question. I ended up using the example for WPF here: http://www.c-sharpcorner.com/UploadFile/f9f215/how-to-restrict-the-application-to-just-one-instance/

public partial class App : Application  
{  
    private static Mutex _mutex = null;  

    protected override void OnStartup(StartupEventArgs e)  
    {  
        const string appName = "MyAppName";  
        bool createdNew;  

        _mutex = new Mutex(true, appName, out createdNew);  

        if (!createdNew)  
        {  
            //app is already running! Exiting the application  
            Application.Current.Shutdown();  
        }  

    }          
}  

In App.xaml:

x:Class="*YourNameSpace*.App"
StartupUri="MainWindow.xaml"
Startup="App_Startup"

Answer 6

[STAThread]
static void Main()                  // args are OK here, of course
{
    bool ok;
    m = new System.Threading.Mutex(true, "YourNameHere", out ok);

    if (! ok)
    {
        MessageBox.Show("Another instance is already running.");
        return;
    }

    Application.Run(new Form1());   // or whatever was there

    GC.KeepAlive(m);                // important!
}

From: Ensuring a single instance of .NET Application

and: Single Instance Application Mutex

Same answer as @Smink and @Imjustpondering with a twist:

Jon Skeet's FAQ on C# to find out why GC.KeepAlive matters