How can I check for a running process per user session?

Question

I have a .NET application that I only allow to run a single process at a time of, however that app is used on Citrix boxes from time to time, and as such, can be run by multiple users on the same machine.

I want to check and make sure that the application is only running once per user session, because right now if user A is running the app, then user B gets the "App already in use" message, and should not.

This is what I have now that checks for the running process:

Process[] p = Process.GetProcessesByName(Process.GetCurrentProcess().ProcessName);
            if (p.Length > 1)
            {
#if !DEBUG
                allowedToOpen &= false;
                errorMessage +=
                    string.Format("{0} is already running.{1}", Constants.AssemblyTitle, Environment.NewLine);
#endif
            }

Answer 1

EDIT: Improved the answer according to this cw question ...

You can use a mutex for checking wether the app already runs:

using( var mutex = new Mutex( false, AppGuid ) )
{
    try
    {
        try
        {
            if( !mutex.WaitOne( 0, false ) )
            {
                MessageBox.Show( "Another instance is already running." );
                return;
            }
        }
        catch( AbandonedMutexException )
        {
            // Log the fact the mutex was abandoned in another process,
            // it will still get aquired
        }

        Application.Run(new Form1());
    }
    finally
    {
        mutex.ReleaseMutex();
    }
}

Important is the AppGuid - you could make it depend on the user.

Maybe you like to read this article: the misunderstood mutex

Answer 2

As tanascius already say, you can use the Mutex.

On a server that is running Terminal Services, a named system mutex can have two levels of visibility. If its name begins with the prefix "Global\", the mutex is visible in all terminal server sessions. If its name begins with the prefix "Local\", the mutex is visible only in the terminal server session where it was created.

Source: msdn, Mutex Class

Answer 3

Just stating the obvious - although Mutex is usually considered better solution, you can still solve the single-instance-per-session issue without Mutex - just test the SessionId as well.

    private static bool ApplicationIsAlreadyRunning()
    {
        var currentProcess = Process.GetCurrentProcess();
        var processes = Process.GetProcessesByName(currentProcess.ProcessName);

        // test if there's another process running in current session.
        var intTotalRunningInCurrentSession = processes.Count(prc => prc.SessionId == currentProcess.SessionId);

        return intTotalRunningInCurrentSession > 1;
    }

Source (no Linq)