CreateProcessAsUser Multiple Application Instances?

Question

The steps you outlined above will generate one process per execution of the method createProcessAsUser(). Now this method does not contain any code to terminate or kill the process so repeatidly calling this method will generate more than one process. As your code is displayed the method will inface generate only one process.

I think the real answer is how are you calling this method. As you stated in the comment

I'm trying to launch the .exe in the user session

I can only assume you may be calling this process from the Session start, Application_BeginRequest or another method that may be executed multiple times depending on how your application is designed (the calling code for this method would be great as an edit).

As I stated earlier the exe is being executed every time the method is called and not terminated. If you only ever want one instance of the application running you will have to examine the process tree to identify if the process is already running. Now if you should have one process running per user you will need to do the above but also maintain a reference the process ID that was created the first time the application started.

Review the code below for the changes (simplified)

public void createProcessAsUser()
{
    //one process per session
    object sessionPID = Session["_servicePID"];
    if (sessionPID != null && sessionPID is int && Process.GetProcessById((int)sessionPID) != null)
        return; //<-- Return process already running for session
    else
        Session.Remove("_servicePID");

    //one process per application
    object applicationPID = Application["_applicationPID"];
    if (applicationPID != null && applicationPID is int && Process.GetProcessById((int)applicationPID) != null)
        return; //<-- Process running for application
    else
        Application.Remove("_applicationPID");

    //omitted starting code

    if (ret == false)
        // omitted log failed
    else
    {
        // omitted log started

        //for one process per session
        Session["_servicePID"] = Convert.ToInt32(pi.dwProcessId);

        //for one process per application
        Application["_applicationPID"] = Convert.ToInt32(pi.dwProcessId);

        //close handles
    }

    // omitted the rest of the method
}

This simple saves a reference to the Process ID that was created for the application into either the Session state for one process per user or the Application state for one process per application instance.

Now if this is the intended result you may also want to look at Terminating the process either when the application shutdown (gracefully) or the session ends. That would be very similar to our first check but can be done as seen below. *note this doesn't take into account the worker process shutting down without calling the session \ application end events those should be handled as well possibly in the application start.

//session end
void Session_End(object sender, EventArgs e)
{
    object sessionPID = Session["_servicePID"];
    if (sessionPID != null && sessionPID is int)
    {
        Process runningProcess = Process.GetProcessById((int)sessionPID);
        if (runningProcess != null)
            runningProcess.Kill();
    }
}

//application end
void Application_End(object sender, EventArgs e)
{
    object applicationPID = Application["_applicationPID"];
    if (applicationPID != null && applicationPID is int && Process.GetProcessById((int)applicationPID) != null)
    {
        Process runningProcess = Process.GetProcessById((int)applicationPID);
        if (runningProcess != null)
            runningProcess.Kill();
    }
}

Again, back to the original question how do you stop the multiple instances. The answer is simply stop the ability to spawn multiple instances by examining how you start the instances (I.e. the calling code to the method createProcessAsUser()) and adjust your method accordingly to avoid multiple calls.

Please post an edit if this inst helpful with details on how the createProcessAsUser() method is called.

Update 1:

Session \ Application does not exist in the context. This will happen if the method createProcessUser() is in a different class than an ASPX page (as it is on the tutorial).

Because of this you will need to change for the existance of an HttpContext this can simply done by calling

HttpContext.Currrent

I have adapted the method above to include checks to the HttpContext

public void createProcessAsUser()
{
    //find the http context
    var ctx = HttpContext.Current;
    if (ctx == null)
        throw new Exception("No Http Context");

    //use the following code for 1 process per user session
    object sessionPID = ctx.Session["_servicePID"];
    if (sessionPID != null && sessionPID is int && Process.GetProcessById((int)sessionPID) != null)
        return; //<-- Return process already running for session
    else
        ctx.Session.Remove("_servicePID");

    //use the following code for 1 process per application instance
    object applicationPID = ctx.Application["_applicationPID"];
    if (applicationPID != null && applicationPID is int && Process.GetProcessById((int)sessionPID) != null)
        return; //<-- Process running for application
    else
        ctx.Application.Remove("_applicationPID");

    // omitted code

    if (ret == false)
    {
        //omitted logging
    }
    else
    {
        //omitted logging

        CloseHandle(pi.hProcess);
        CloseHandle(pi.hThread);


        //for one process per session
        ctx.Session["_servicePID"] = Convert.ToInt32(pi.dwProcessId);

        //for one process per application
        ctx.Application["_applicationPID"] = Convert.ToInt32(pi.dwProcessId);
    }

    //omitted the rest
}

You will not the changes are in the first few lines where it gets the current HttpContext (you must add using System.Web) by calling var ctx = HttpContext.Current

Next we just check that the ctx variable is not null. If it is null I am throwing an exception, however you can handle this anyway you wish.

From there instead of directly calling Session and Application I have changed the references to ctx.Session... and ctx.Application...

Update 2:

This is a Windows Application calling the method above. Now this changes the ball game as the code above is really meant to start a process as the impersonated windows identity. Now Impersonation is typcially done in WebApplications not WinForms (can be done though).

If you are not impersonating a different user than the user who is running the application. Meaning the user logged in is the user that is running the application. If this is so then your code becomes ALOT easier.

Below is an example of how this can be achieved.

/// <summary>
/// static process ID value
/// </summary>
static int? processID = null;

public void startProcess()
{
    //check if the processID has a value and if the process ID is active
    if (processID.HasValue && Process.GetProcessById(processID.Value) != null)
        return;

    //start a new process
    var process = new Process();
    var processStartInfo = new ProcessStartInfo(@"C:\myProg.exe");
    processStartInfo.CreateNoWindow = true;
    processStartInfo.UseShellExecute = false;
    process.StartInfo = processStartInfo;
    process.Start();
    //set the process id
    processID = process.Id;
}

Again as this is a Win Forms application you can use the Process object to launch a process, this windows application will run as the user running the Windows Forms application. In this example we also hold a static reference to the processID and check the if the processID (if found) is already running.