As was explained, server threads are automatically spawned by the RPC runtime in the server manager to handle incoming remote procedure calls from clients. The number of calls that can be concurrently handled depends on the value of the max_calls_exec parameter specified in the call to rpc_server_listen( ). The thread is created by the RPC runtime and begins execution in the operation requested. When the operation is completed, the thread is automatically terminated (by the RPC runtime).
See also the OSF DCE Application Development Guide - Core Components and the OSF DCE Application Development Reference for a comprehensive discussion of DCE threads.
More:
Getting the Client's Credentials
Making the Authorization Decision
Returning the Results and Resuming Listening