Callbacks from unmanaged code...

[Guest]

Hi there,

I'm new to C# (but not to C++), and I'm trying to create a web service that
calls some of our older software, located in a DLL. I'm getting most the
calls to work ok, but one of them needs a callback into the managed code. I
thought I had it all worked out, but it seems like when the callback is
getting hit, things might be going out of scope and crashing the app.

Here's my little web service function; I hacked out a bunch of other stuff
for brevity, but the general idea is, I call the "Initialize" function,
providing a callback to the DLL so the DLL can call me when certain
operations in the "LoginUser2" complete.

You can see where I tried to keep the callback around in a session object,
but, being a novice, I'm not sure this is the right approach. Essentially, I
need this callback alive for the whole life of the user's session.

[WebMethod(EnableSession = true)]
public string HelloArguments(string sLogin, string sPassword)
{
Test.TNInitializeCallbackType cb = new
Test.TNInitializeCallbackType(Test.TNAPICallback);
Session["Callback"] = cb;

hWho = Test.Initialize(cb);

result2 = Test.LogonUser2(hWho, sLogin, sPassword);

return sResult;
}

and some defs:

class Test
{
[DllImport("mydll.dll")]
public static extern Int32 LogonUser2(IntPtr hWho, string pszLogin,
string pszPassword);

public delegate IntPtr TNInitializeCallbackType(IntPtr hWho, Int32
a1, Int32 a2, Int32 a3);

[DllImport("mydll.dll")]
public static extern IntPtr Initialize(TNInitializeCallbackType
callback);

public static IntPtr TNAPICallback(IntPtr hWho, Int32 a1, Int32 a2,
Int32 a3)
{
return (IntPtr)0;
}

Thanks for any help or pointers as to where I can read up on this.

 

[Guest]

In .NET, the calling convention for methods is StdCall. What is the calling
convention for your unmanaged *.dll? I'm assumming it is probably cdecl,
which will cause problems in your managed callback. The stack is probably
being popped one too many times after your call back executes.

You can use the CallingConvention property of the DllImport attribute to
define the calling convention for that method, but I'm not sure if this can
be applied to delegates.

[DllImport("mydll.dll", CallingConvention=CallingConvention.Cdecl )]
public static extern IntPtr Initialize(TNInitializeCallbackType callback);

Not sure if the above code will work for a delegate, but you can give it a
shot. If you have the unmanaged souce code, you can probably create another
method called something like "InitializeStdCall" using the StdCall calling
convention and then in there, call "Initialize". This will act as a wrapper.

Hope this helps or points you in the right direction.

 

[Guest]

Hi - thanks for your response!

The definition is actually __stdcall in the unmanaged code; here's the C++
prototype definition for the callback that has to be passed to C++:

typedef long (*TNAPI_CALLBACK)(HANDLE, DWORD, DWORD, DWORD);
HANDLE CALLBACK TN_Initialize(TNAPI_CALLBACK pFunc);

So the idea is that in C# I need to call TN_Initilalize and pass it a
callback function, so that the unmanaged DLL can make calls to the provided
callback.

It seems to be (mostly) working; I can set breakpoints in the C# provided
callback, and it's getting called...but I think something's munged because
sometimes the app just croaks.

In .NET, the calling convention for methods is StdCall. What is the calling
convention for your unmanaged *.dll? I'm assumming it is probably cdecl,
which will cause problems in your managed callback. The stack is probably
being popped one too many times after your call back executes.

You can use the CallingConvention property of the DllImport attribute to
define the calling convention for that method, but I'm not sure if this can
be applied to delegates.

[DllImport("mydll.dll", CallingConvention=CallingConvention.Cdecl )]
public static extern IntPtr Initialize(TNInitializeCallbackType callback);

Not sure if the above code will work for a delegate, but you can give it a
shot. If you have the unmanaged souce code, you can probably create another
method called something like "InitializeStdCall" using the StdCall calling
convention and then in there, call "Initialize". This will act as a wrapper.

Hope this helps or points you in the right direction.

Hi there,

I'm new to C# (but not to C++), and I'm trying to create a web service that
calls some of our older software, located in a DLL. I'm getting most the
calls to work ok, but one of them needs a callback into the managed code. I
thought I had it all worked out, but it seems like when the callback is
getting hit, things might be going out of scope and crashing the app.

Here's my little web service function; I hacked out a bunch of other stuff
for brevity, but the general idea is, I call the "Initialize" function,
providing a callback to the DLL so the DLL can call me when certain
operations in the "LoginUser2" complete.

You can see where I tried to keep the callback around in a session object,
but, being a novice, I'm not sure this is the right approach. Essentially, I
need this callback alive for the whole life of the user's session.

[WebMethod(EnableSession = true)]
public string HelloArguments(string sLogin, string sPassword)
{
Test.TNInitializeCallbackType cb = new
Test.TNInitializeCallbackType(Test.TNAPICallback);
Session["Callback"] = cb;

hWho = Test.Initialize(cb);

result2 = Test.LogonUser2(hWho, sLogin, sPassword);

return sResult;
}

and some defs:

class Test
{
[DllImport("mydll.dll")]
public static extern Int32 LogonUser2(IntPtr hWho, string pszLogin,
string pszPassword);

public delegate IntPtr TNInitializeCallbackType(IntPtr hWho, Int32
a1, Int32 a2, Int32 a3);

[DllImport("mydll.dll")]
public static extern IntPtr Initialize(TNInitializeCallbackType
callback);

public static IntPtr TNAPICallback(IntPtr hWho, Int32 a1, Int32 a2,
Int32 a3)
{
return (IntPtr)0;
}

Thanks for any help or pointers as to where I can read up on this.