如何知道Windows服务是否有活动的交互式会话？

Question

I'm coding a windows service and in one point I need to know if there is an active interactive session.

I tried using OnSessionChange() and keep in a variable the last SessionChangeReason. When I reach to the mentioned point I compare if it's equal to SessionChangeReason.SessionLogOn. This works with the inconvenient that the service has a delayed start so if the user logs on before the service starts running this information is lost.

I have also seen the System.Environment.Interactive property but as I understand this refers to the process of the current service which is not interactive, so it wouldn't give me the information I need (I might misunderstood this, though).

Is there a way to get this info 'on demand' without having to keep register of the SessionChangeReason?

Edit: Maybe I wasn't clear about this point. Aside from knowing that there is an interactive session I also need to know that it isn't locked.

Answer 1

P/Invoke WTSEnumerateSessions to see if there are additional sessions and what their connected states are. You obviously have to ignore session 0 on Vista+.

You should only do this when your service is started, the session change notification should be used to detect further changes.

Answer 2

Finally I've resigned to knowing specifically that there is a session and isn't locked so we'll work with whether there is an active session or not.

If only knowing there is an active session works for you and you don't want to use pInvoke you can either:

a) Search for the explorer process

Process[] ps = Process.GetProcessesByName("explorer");
bool explorerActive = (ps.Length > 0);

b) Use the following WMI query to get the UserName of the active session:

using System.Management;

ConnectionOptions oConn = new ConnectionOptions();
ManagementScope oMs = new ManagementScope("\\\\localhost", oConn);

ObjectQuery oQuery = new ObjectQuery("select * from Win32_ComputerSystem");
ManagementObjectSearcher oSearcher = new ManagementObjectSearcher(oMs, oQuery);
ManagementObjectCollection oReturnCollection = oSearcher.Get();


foreach (ManagementObject oReturn in oReturnCollection)
{
    if (oReturn["UserName"] == null)
    {
        // No active session
        Console.Write("UserName: null");
    }
    else
    {
        // Active session
        Console.Write("UserName: " + oReturn["UserName"].ToString());
    }                            
}

If you want to use pInvoke see Anders' answer.