public static void Unregister(int instanceId, IntPtr serviceHandle)
{
// This method could be called by the GC finalizer thread. If it is then a direct call to the DDEML will fail since the DDEML is
// thread specific. A message will be posted to the DDEML thread instead.
lock (_Table)
{
if (_Table.ContainsKey(serviceHandle))
{
// Determine if the current thread matches what is in the table.
int threadId = (int)_Table[serviceHandle];
if (threadId == Ddeml.GetCurrentThreadId())
{
// Unregister the service name.
Ddeml.DdeNameService(instanceId, serviceHandle, IntPtr.Zero, Ddeml.DNS_UNREGISTER);
// Free the service string handle.
Ddeml.DdeFreeStringHandle(instanceId, serviceHandle);
}
else
{
// Post a message to the thread that needs to execute the Ddeml.DdeXXX methods.
PostThreadMessage(threadId, WM_APP + 3, new IntPtr(instanceId), serviceHandle);
}
// Remove the service handle from the table because it is no longer in use.
_Table.Remove(serviceHandle);
}
}
}
public static IntPtr Register(int instanceId, string service)
{
lock (_Table)
{
// Create a string handle for the service name.
IntPtr serviceHandle = Ddeml.DdeCreateStringHandle(instanceId, service, Ddeml.CP_WINANSI);
// Register the service name.
IntPtr result = Ddeml.DdeNameService(instanceId, serviceHandle, IntPtr.Zero, Ddeml.DNS_REGISTER);
if (result != IntPtr.Zero)
{
// Make sure this thread has an IMessageFilter on it.
LocalDataStoreSlot slot = Thread.GetNamedDataSlot(DataSlot);
if (Thread.GetData(slot) == null)
{
RegistrationManager filter = new RegistrationManager();
Application.AddMessageFilter(filter);
Thread.SetData(slot, filter);
}
// Add an entry to the table that maps the service handle to the current thread.
_Table.Add(serviceHandle, Ddeml.GetCurrentThreadId());
}
else
{
// Free the string handle created earlier.
Ddeml.DdeFreeStringHandle(instanceId, serviceHandle);
serviceHandle = IntPtr.Zero;
}
return serviceHandle;
}
}
bool IMessageFilter.PreFilterMessage(ref Message m)
{
if (m.Msg == WM_APP + 3)
{
// Unregister the service name.
Ddeml.DdeNameService(m.WParam.ToInt32(), m.LParam, IntPtr.Zero, Ddeml.DNS_UNREGISTER);
// Free the service string handle.
Ddeml.DdeFreeStringHandle(m.WParam.ToInt32(), m.LParam);
}
return false;
}