Last Modified September 29, 2026
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Implementing MUTEX protection

MUTEX protection will allow just one instance of the Application to be running on a given computer / server.

You would typically apply this strategy for an enterprise application to protect against the following:

  • the Application running on a computer accessed by multiple users using Remote Desktop to run multiple instances of the application simultaneously
  • the Application being run on a Server with multiple concurrent instances of the Application

The implementation requires a change to the main program file to create a MUTEX, detect if the Application is already running and taking an action if an instance is already running (ex: stop the application, bring the current instance to the forefront, ...).

In the code sample page, we have included a MUTEX variant of the HelloWord C# Win32 code sample, where we have replaced the program.cs code as follows:

                    
                    
                    	// non-MUTEX version of program.cs of HelloWorld project
                        
                        using System;
                        using System.Collections.Generic;
                        using System.Linq;
                        using System.Threading.Tasks;
                        using System.Windows.Forms;
                        
                        namespace HelloWorld
                        {
                            static class Program
                            {
                                /// 
                                /// The main entry point for the application.
                                /// 
                                [STAThread]
                                static void Main()
                                {
                                    Application.EnableVisualStyles();
                                    Application.SetCompatibleTextRenderingDefault(false);
                                    Application.Run(new HelloWorld());
                                }
                            }
                        }
                    
                    
                    
                    
                    	// MUTEX version of program.cs of HelloWorld project
                        
                        using System;
                        using System.Collections.Generic;
                        using System.Linq;
                        using System.Threading.Tasks;
                        using System.Threading;
                        using System.Runtime.InteropServices;
                        using System.Windows.Forms;
                        
                        namespace HelloWorld
                        {
                            static class Program
                            {
                                /// 
                                /// The main entry point for the application.
                                /// 
                                [STAThread]
                                static void Main()
                                {
                                    // set up MUTEX, and run only if this is only instance of the App HelloWorld
                                    
                                    bool createdNew = true;
                                    using (Mutex mutex = new Mutex(true, "HelloWorld", out createdNew))
                                    {
                                        if (createdNew)
                                        {
                                            Application.EnableVisualStyles();
                                            Application.SetCompatibleTextRenderingDefault(false);
                                            Application.Run(new HelloWorld());
                                        }
                                        else
                                        {
                                            // code for when more than one instance is running
                                            //
                                            // here we just show message box message
                                            MessageBox.Show("HelloWorld is already running.");
                                        }
                                    }
                                 }
                            }
                        }