I have written a C++ DDE client (console) app that talks to a third party dde server. This works fine when my client and server are in the same session. I then moved my client code into a win32 service running as SYSTEM. The client code is unable to get a server list in spite of trying the following: 1. I tried to enable "Allow service to interact with desktop" on Win7. 2. I have impersonated the user in the thread that tries to talk to the server. 3 I have tried to execute the client code as system.
I can understand the primary issue being comms across multiple sessions. But is there any way of achieving elegantly?
Starting with Vista, "interactive" services do not work anymore, because of Session 0 Isolation.
DDE is a User32-based technology (it uses window messages internally), and as such cannot be used across session boundaries.
To do what you are attempting, you will have to create a separate non-service app that runs in the context of a user session and uses DDE as needed, communicating back and forth with the service via a session-agnostic IPC mechanism, such as a named pipe, socket, or COM object. The service can use
WTSQueryUserToken()andCreateProcessAsUser()to run the app within a specific user session when needed. Or you can configure the app to auto-run when a user logs in.