What is the safest way to prevent multiple instances of a program?

Question

I am trying to prevent my program from running multiple instances at any given time. I have read about using mutex and windows events, however both threads were several years old, and I'm curious if with .net4 there is a more simple, and more elegant way to deal with this? I thought I had read about a setting for the form that allowed you to deny multiple instances by the property? Could someone shed some light on what the safest and/or simplest way to prevent multiple instances of a program is?

The safest way is to use the built-in support in .NET, WindowsFormsApplicationBase.IsSingleInstance property. Hard to guess if it is appropriate, you didn't make much effort describing your exact needs. And no, nothing changed in the past 5 years. — Hans Passant, Jan 07 '12 at 00:38
Create a named event. Take a look on how to do it [here][1] [1]: http://stackoverflow.com/questions/447546/creating-win32-events-from-c-sharp — Odys, Jan 07 '12 at 00:42
Hans if you'll make that comment an actual answer I'll award you with the chosen answer. — Fuzz Evans, Jan 22 '12 at 20:09

score 5 · Accepted Answer · answered Jun 04 '12 at 18:41

The safest way is to use the built-in support in .NET, WindowsFormsApplicationBase.IsSingleInstance property. Hard to guess if it is appropriate, you didn't make much effort describing your exact needs. And no, nothing changed in the past 5 years. – Hans Passant Jan 7 at 0:38

This was the best answer but Hans didn't submit it as an answer.

Sam Axe · Answer 2 · 2012-01-07T01:05:38.377

In VB you can set this at the project level (Properties > General) for Winforms projects.

In C# you can use code similar to this.. needs conversion of course..

Dim tGrantedMutexOwnership As Boolean = False
Dim tSingleInstanceMutex As Mutex = New Mutex(True, "MUTEX NAME HERE", tGrantedMutexOwnership)

If Not tGrantedMutexOwnership Then
'
' Application is already running, so shut down this instance
'
Else
' 
' No other instances are running
'
End If

Whoops, I forgot to mention that you will need to place GC.KeepAlive(tSingleInstanceMutex) after your Application.Run() call

score 1 · Answer 3 · answered Jan 06 '13 at 09:48

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Windows.Forms;

namespace YourNameSpaceGoesHere
{
    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {

            if (Process.GetProcessesByName("YourFriendlyProcessNameGoesHere").Length > 1)
            {
                MessageBox.Show(Application.ProductName + " already running!");
                Application.ExitThread();
            }
            else
            {
                Application.EnableVisualStyles();
                Application.SetCompatibleTextRenderingDefault(false);
                Application.Run(new YourStartUpObjectFormNameGoesHere());
            }

        }
    }
}

What is the safest way to prevent multiple instances of a program?

3 Answers3