WindowsFormsApplicationBase.IsSingleInstance applications are global on a machine, not per user #3715
Description
-
.NET Core Version:
v5.0.0-preview.7 -
Have you experienced this same bug with .NET Framework?:
No
Problem description:
The implementation of WindowsFormsApplicationBase.IsSingleInstance from #3200 uses a named pipe as its synchronization and communication tool, but named pipes are in a global namespace (at least on Windows) and thus any assembly can only be running once on any given machine.
Expected behavior:
Able to start this executable in multiple user accounts (under terminal services or fast user switching) at once.
Actual behaviour:
Starting the executable in a second user account produces an uncaught CantStartSingleInstanceException exception.
Strictly speaking this is a potential denial of service issue; by using a named pipe with a predictable name, users can prevent others on the same machine from ever starting the application. Adding the session identifier to the pipe name is enough to make the named pipe session-local, but not enough to prevent others from creating a pipe with the same name.
I don't know what other options there are; mutexes and event handles have a session namespace, but don't allow for data transfer. Local TCP runs into trouble with firewalls (as the old Remoting implementation did). Cursory reading shows that named memory mappings are Windows only, and require marshalling/synchronisation to a much greater degree, though perhaps a memory mapping containing only the randomly-generated named pipe name is the way to go (like WCF).
Minimal repro:
Borrowed from https://stackoverflow.com/a/19326/125549:
public class SingleInstanceApplication : System.Windows.Application
{
protected override void OnStartup(System.Windows.StartupEventArgs e)
{
// Call the OnStartup event on our base class
base.OnStartup(e);
// Create our MainWindow and show it
MainWindow window = new MainWindow();
window.Show();
}
public void Activate()
{
// Reactivate the main window
MainWindow.Activate();
}
}
public class SingleInstanceManager : Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase
{
private SingleInstanceApplication _application;
private System.Collections.ObjectModel.ReadOnlyCollection<string> _commandLine;
public SingleInstanceManager()
{
IsSingleInstance = true;
}
protected override bool OnStartup(Microsoft.VisualBasic.ApplicationServices.StartupEventArgs eventArgs)
{
// First time _application is launched
_commandLine = eventArgs.CommandLine;
_application = new SingleInstanceApplication();
_application.Run();
return false;
}
protected override void OnStartupNextInstance(StartupNextInstanceEventArgs eventArgs)
{
// Subsequent launches
base.OnStartupNextInstance(eventArgs);
_commandLine = eventArgs.CommandLine;
_application.Activate();
}
}
public class EntryPoint
{
[STAThread]
public static void Main(string[] args)
{
SingleInstanceManager manager = new SingleInstanceManager();
manager.Run(args);
}
}