Delegate not called from win32 api in C# windows service

[gushie]

I have a C# library which calls TAPI2 Win32 methods, declared using DllImport (tapi32.dll).

 

One of these routines is passed a delegate, which should then be frequently called by Tapi.

 

If I use my library from a Windows Form application, then all works well and my callback is successfully called.

However, if I use it from a Windows service, then although everything else works, my delegate never gets called.

 

I have searched for reasons why this may be the case, and found that the ApartmentState may have something to do with it, but adding a [sTAThread] before the Main() function in the service hasn't made any difference.

 

Does anyone know anything else I may need to do?

 

Thanks,

Jonathan Corwin.

[PlausiblyDamp]

Could you post the relevant code? Or at least give afew more details about what the callback function does.

[gushie]

Could you post the relevant code? Or at least give afew more details about what the callback function does.

 

Yes, here is the code. I was just initially checking there wasn't anything "obvious" that I may not have done. (I'm relatively new to .Net)

 

Relevant bits from the service:

namespace CtiServerCS
{
public class Service1 : System.ServiceProcess.ServiceBase
{
	BMSTapi.Tapi t;
	BMSTapi.NetworkUserCollection u;
	BMSTapi.NetworkListener nl;
	private System.ComponentModel.Container components = null;

	public Service1()
	{
		InitializeComponent();
	}

	[sTAThread]
	static void Main()
	{
		System.ServiceProcess.ServiceBase[] ServicesToRun;
		ServicesToRun = new System.ServiceProcess.ServiceBase[] { new Service1() };
		System.ServiceProcess.ServiceBase.Run(ServicesToRun);
	}
	protected override void OnStart(string[] args)
	{
		t = new BMSTapi.Tapi();
		u = new BMSTapi.NetworkUserCollection();
		nl = new BMSTapi.NetworkListener(t, u);
		nl.Start();
	}
...
}
}

 

And relevant bits from the BMSTapi library:

 

namespace BMSTapi
{
public class Tapi
{

[structLayout(LayoutKind.Sequential)]
public struct LineInitializeExParams
{
	public uint dwTotalSize;
	public uint dwNeededSize;
	public uint dwUsedSize;
	public uint dwOptions;
	public System.IntPtr hEvent;
	public System.IntPtr hCompletionPort;
	public uint dwCompletionKey;
}

	private System.IntPtr _hTapi;
	private LineCallBackFunc _hCallBackFunc;

	public delegate void LineCallBackFunc(uint hDevice, uint dwMsg, uint dwCallbackInstance,
		uint dwParam1, uint dwParam2, uint dwParam3);

	[DllImport("Tapi32.dll", EntryPoint="lineInitializeExW", CharSet=CharSet.Auto, SetLastError=true)]
	internal static extern LineErrReturn lineInitializeEx(
		out IntPtr hLineApp, 
		IntPtr hAppHandle, 
		LineCallBackFunc lCallBack,
		string FriendlyAppName, 
		out uint NumDevices, 
		ref uint APIVersion,
		ref LineInitializeExParams lineExInitParams);

	public TapiApi.LineCallBackFunc CallBackFunc
	{
		get
		{
			return _hCallBackFunc;
		}
	}
	public Tapi()
	{
		InitialiseTapi();
	}
	
	public void LineEventHandler(uint dwDevice, uint dwMsg, uint dwCallbackInstance,
		uint dwParam1, uint dwParam2, uint dwParam3)
	{
			
		// Code that never ever gets reached from the service, but does from the form
	}

	private void InitialiseTapi()
	{
		LineErrReturn ret;
		uint apiVers = TapiConstants.ApiHighVers;

		LineInitializeExParams tapiParams = new LineInitializeExParams();
		tapiParams.dwTotalSize = (uint) Marshal.SizeOf(tapiParams);
		tapiParams.dwNeededSize = tapiParams.dwTotalSize;
		tapiParams.dwUsedSize = tapiParams.dwUsedSize;
		tapiParams.dwOptions = (uint)LineInitializeExOptions.UseHiddenWindow;
		tapiParams.hEvent = System.IntPtr.Zero;
		tapiParams.hEvent = System.IntPtr.Zero;
		tapiParams.hCompletionPort = System.IntPtr.Zero;
		_hCallBackFunc = new TapiApi.LineCallBackFunc(LineEventHandler);
		ret = lineInitializeEx(out _hTapi, System.IntPtr.Zero, _hCallBackFunc, "BMSTAPI", out _lineCnt, ref apiVers, ref tapiParams);
	}
}

public class NetworkListener
{
	private TcpListener _netListen;
	private System.Timers.Timer _netClientTimer;
	private Tapi _tapi;
	private NetworkUserCollection _users;    
	private NetworkClientCollection _netClients = new NetworkClientCollection();

	public NetworkListener(Tapi tapi, NetworkUserCollection users)
	{
		_netListen = new TcpListener(IPAddress.Parse("0.0.0.0"), 33334);
		_netClientTimer = new System.Timers.Timer();
		_netClientTimer.Interval = 500;
		_netClientTimer.Elapsed+=new ElapsedEventHandler(netClientTimer_Elapsed);
	}
	public void Start()
	{
		_netListen.Start();
		_netClientTimer.Start();
		_tapi.EventMessage("Started");
	}
	private void netClientTimer_Elapsed(object sender, ElapsedEventArgs e)
	{
		TcpClient client;
		NetworkClient netClient;
		if(_netListen.Pending())
		{
			client = _netListen.AcceptTcpClient();
			netClient = new NetworkClient(client, _tapi, _users);
			_netClients.Add(netClient);
			Thread t = new Thread(new ThreadStart(netClient.Start));
			t.ApartmentState = ApartmentState.STA;	//Added to see if this made a difference
			t.Start();
		}
	}
}
}

[Derek Stone]

Make sure that the garbage collector isn't disposing your delegate prior to the callback function being invoked by TAPI.

 

You might need to call [msdn=System.GC.KeepAlive]GC.KeepAlive()[/msdn] on the object.

[gushie]

The problem ended up being down to me not reading the Tapi documentation properly, so apologies for taking up your time.

 

For anyone who may be interested:

I was calling lineInitializeEx with a parameter USEHIDDENWINDOW, which tells the routine to use a hidden window for its event handling. As no message queue exists in a windows service, the messages didn't get very far.

Using the USEEVENT parameter instead, and using the lineGetMessage routine to get the messages rather than a delegate solved the problem.