How to implement single instance per machine application?

Question

I have to restrict my .net 4 WPF application so that it can be run only once per machine. Note that I said per machine, not per session.
I implemented single instance applications using a simple mutex until now, but unfortunately such a mutex is per session.

Is there a way to create a machine wide mutex or is there any other solution to implement a single instance per machine application?

Answer 1

I would do this with a global Mutex object that must be kept for the life of your application.

MutexSecurity oMutexSecurity;

//Set the security object
oMutexSecurity = new MutexSecurity();
oMutexSecurity.AddAccessRule(new MutexAccessRule(new SecurityIdentifier(WellKnownSidType.BuiltinUsersSid, null), MutexRights.FullControl, AccessControlType.Allow));

//Create the global mutex and set its security
moGlobalMutex = new Mutex(True, "Global\\{5076d41c-a40a-4f4d-9eed-bf274a5bedcb}", bFirstInstance);
moGlobalMutex.SetAccessControl(oMutexSecurity);

Where bFirstInstance returns if this is the first instance of your application running globally. If you omited the Global part of the mutex or replaced it with Local then the mutex would only be per session (this is proberbly how your current code is working).

I believe that I got this technique first from Jon Skeet.

The MSDN topic on the Mutex object explains about the two scopes for a Mutex object and highlights why this is important when using terminal services (see second to last note).

Answer 2

I think what you need to do is use a system sempahore to track the instances of your application.

If you create a Semaphore object using a constructor that accepts a name, it is associated with an operating-system semaphore of that name.

Named system semaphores are visible throughout the operating system, and can be used to synchronize the activities of processes.

EDIT: Note that I am not aware if this approach works across multiple windows sessions on a machine. I think it should as its an OS level construct but I cant say for sure as i havent tested it that way.

EDIT 2: I did not know this but after reading Stevo2000's answer, i did some looking up as well and I think that the "Global\" prefixing to make the the object applicable to the global namespace would apply to semaphores as well and semaphore, if created this way, should work.

Answer 3

You could open a file with exclusive rights somewhere in %PROGRAMDATA% The second instance that starts will try to open the same file and fail if it's already open.

Answer 4

How about using the registry?

1. You can create a registry entry under HKEY_LOCAL_MACHINE.
2. Let the value be the flag if the application is started or not.
3. Encrypt the key using some standard symmetric key encryption method so that no one else can tamper with the value.
4. On application start-up check for the key and abort\continue accordingly.
5. Do not forget to obfuscate your assembly, which does this encryption\decryption part, so that no one can hack the key in registry by looking at the code in reflector.

Answer 5

I did something similar once.

When staring up the application list, I checked all running processes for a process with identical name, and if it existed I would not allow to start the program.

This is not bulletproof of course, since if another application have the exact same process name, your application will never start, but if you use a non-generic name it will probably be more than good enough.

Answer 6

For the sake of completeness, I'd like to add the following which I just found now:
This web site has an interesting approach in sending Win32 messages to other processes. This would fix the problem of the user renaming the assembly to bypass the test and of other assemblies with the same name.
They're using the message to activate the main window of the other process, but it seems like the message could be a dummy message only used to see whether the other process is responding to it to know whether it is our process or not.

Note that I haven't tested it yet.

Answer 7

See below for full example of how a single instace app is done in WPF 3.5

public class SingleInstanceApplicationWrapper :
Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase
{
public SingleInstanceApplicationWrapper()
{
// Enable single-instance mode.
this.IsSingleInstance = true;
}
// Create the WPF application class.
private WpfApp app;
protected override bool OnStartup(
Microsoft.VisualBasic.ApplicationServices.StartupEventArgs e)
{
app = new WpfApp();
app.Run();
return false;
}
// Direct multiple instances.
protected override void OnStartupNextInstance(
Microsoft.VisualBasic.ApplicationServices.StartupNextInstanceEventArgs e)
{
if (e.CommandLine.Count > 0)
{
app.ShowDocument(e.CommandLine[0]);
}
}
}

Second part:

public class WpfApp : System.Windows.Application
{
protected override void OnStartup(System.Windows.StartupEventArgs e)
{
base.OnStartup(e);
WpfApp.current = this;
// Load the main window.
DocumentList list = new DocumentList();
this.MainWindow = list;
list.Show();
// Load the document that was specified as an argument.
if (e.Args.Length > 0) ShowDocument(e.Args[0]);
}
public void ShowDocument(string filename)
{
try
{
Document doc = new Document();
doc.LoadFile(filename);
doc.Owner = this.MainWindow;
doc.Show();
// If the application is already loaded, it may not be visible.
// This attempts to give focus to the new window.
doc.Activate();
}
catch
{
MessageBox.Show("Could not load document.");
}
}
}

Third part:

 public class Startup
    {
    [STAThread]
    public static void Main(string[] args)
    {
    SingleInstanceApplicationWrapper wrapper =
    new SingleInstanceApplicationWrapper();
    wrapper.Run(args);
    }
    }

You may need to add soem references and add some using statements but it shoudl work.

You can also download a VS example complete solution by downloading the source code of the book from here.

Taken From "Pro WPF in C#3 2008 , Apress , Matthew MacDonald" , buy the book is gold. I did.