How to prevent same process to be executed more than once at the same time?

Standard Windows Forms applications can be launched multiple times and each instance used completely independently from the others. However, sometimes it is required to restrict the user to run only a single instance of a program.

 Process class 

Process class contains a function that allows us  to get the processes that are currently executing in Windows. This class can be used to find, is there any other instances of an application are running or not.

The following code is performing by checking the number of matching processes and showing an error message if, another instance is already running. The method is then simply returned from to close the application. This has to be done before the main form of the application is loaded.

static void Main() {     // finding existing instances     string processName = Process.GetCurrentProcess().ProcessName;     Process[] instances = Process.GetProcessesByName(processName);     if (instances.Length > 1)     {        MessageBox.Show("This application is already running!");        return;     }         Application.EnableVisualStyles();     Application.SetCompatibleTextRenderingDefault(false);     Application.Run(new Form1()); }

The above code does work perfectly till we have not renamed application. But it does not work, if we renamed application.

For Example,

1.       Open application, lets assume named as “TestApp.exe”. So now one instance of application started

2.       Rename “TestApp.exe” to “TestApp2.exe” and start application. Now second instance also started. But this is not expected.

Let’s see how we can solve this problem also. We can achieve this using Mutex as shown below,

      using System.Diagnostics;

using System.Threading

 [STAThread]

        static void Main()

        {

            bool createdNew;

            Mutex testMutex = new Mutex(true, "singleInstance", out createdNew);

            if (createdNew)

            {

                Application.EnableVisualStyles();

                Application.SetCompatibleTextRenderingDefault(false);

                Application.Run(new Form1());

                testMutex.ReleaseMutex();

            }

            else

            {

                MessageBox.Show("This application is already running.");

                return;

            }

        }

Here, "createdNew" variable will be assigned to false if the mutex object is already created. So, even though we renamed application and start again this will restrict from opening.

That's it, we are done now.