Programmatically Lock workstation from Windows Service

Question

From my Windows Service, I'm trying to lock my Workstation using the below code:

[DllImport("user32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool LockWorkStation();

if (!LockWorkStation()){
 //Workstation was unable to lock(Write this on event log)
}

but the above code is not working.

Anybody has a solution for this?

Answer 1

You can do it with the WTSDisconnectSession Windows API, it will log out user in the same way LockWorkStation does.

However as the service is in a special session, you can't just disconnect WTS_CURRENT_SESSION and have to disconnect every active session on the computer.

using System;
using System.Runtime.InteropServices;

public class LockWorkstation
{
    [DllImport("wtsapi32.dll", SetLastError = true)]
    static extern bool WTSDisconnectSession(IntPtr hServer, int sessionId, bool bWait);

    [DllImport("wtsapi32.dll", SetLastError = true)]
    static extern int WTSEnumerateSessions(IntPtr hServer, int Reserved, int Version, ref IntPtr ppSessionInfo, ref int pCount);

    [DllImport("wtsapi32.dll")]
    static extern void WTSFreeMemory(IntPtr pMemory);

    [StructLayout(LayoutKind.Sequential)]
    private struct WTS_SESSION_INFO
    {
        public Int32 SessionID;

        [MarshalAs(UnmanagedType.LPStr)]
        public String pWinStationName;

        public WTS_CONNECTSTATE_CLASS State;
    }

    private enum WTS_INFO_CLASS
    {
        WTSInitialProgram,
        WTSApplicationName,
        WTSWorkingDirectory,
        WTSOEMId,
        WTSSessionId,
        WTSUserName,
        WTSWinStationName,
        WTSDomainName,
        WTSConnectState,
        WTSClientBuildNumber,
        WTSClientName,
        WTSClientDirectory,
        WTSClientProductId,
        WTSClientHardwareId,
        WTSClientAddress,
        WTSClientDisplay,
        WTSClientProtocolType
    }

    private enum WTS_CONNECTSTATE_CLASS
    {
        WTSActive,
        WTSConnected,
        WTSConnectQuery,
        WTSShadow,
        WTSDisconnected,
        WTSIdle,
        WTSListen,
        WTSReset,
        WTSDown,
        WTSInit
    }

    public static void LockWorkStation()
    {
        IntPtr ppSessionInfo = IntPtr.Zero;
        Int32 count = 0;
        Int32 retval = WTSEnumerateSessions(IntPtr.Zero, 0, 1, ref ppSessionInfo, ref count);
        Int32 dataSize = Marshal.SizeOf(typeof(WTS_SESSION_INFO));
        IntPtr currentSession = ppSessionInfo;

        if (retval == 0) return;

        for (int i = 0; i < count; i++)
        {
            WTS_SESSION_INFO si = (WTS_SESSION_INFO)Marshal.PtrToStructure(currentSession, typeof(WTS_SESSION_INFO));
            if (si.State == WTS_CONNECTSTATE_CLASS.WTSActive) WTSDisconnectSession(IntPtr.Zero, si.SessionID, false);
            currentSession += dataSize;
        }
        WTSFreeMemory(ppSessionInfo);
    }
}