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Using Mutex to restrict number of application instances

Symptoms​

You have created an application (console application example given below) and if two instances were to run then they could interfere with each other.

Cause​

Applications can be run multiple times in Windows. You must write your own restriction to prevent that from happening.

Resolution​

A  mutex (mutual exclusion object) is a program object that is created so that multiple program thread can take turns sharing the same resource, such as access to a file.

The mutex contructor below uses three parameters: bool initiallyOwned, string? name, out bool createdNew 

  • initiallyOwned - should the application request ownership of the mutex created.
  • name - should be unique to this application but shared in all instances of the application, hence using the name of the containing assembly
  • createdNew - indicates if the new mutex was successfully created. Will be false if the mutex of that name already exists.

`Question - will this work between different users logged in to the same machine?

internal class Program { private static Mutex mutex = null;

static void Main(string[] args)
{
    string appName = Assembly.GetExecutingAssembly().GetName().Name;

    bool createdNew;
    mutex = new Mutex(true, appName, out createdNew);

    if (createdNew == false)
    {
        var currentColour = Console.ForegroundColor;
        Console.ForegroundColor = ConsoleColor.Red;
        Console.WriteLine(appName + " is already running! Exiting the application.");
        Console.ForegroundColor = currentColour;
        return;
    }
}

}