A server consists of three parts. First, a "main" program, when run, provides an address space for the objects it manages, and one or more process "threads" that can execute method calls. (Windows and AIX currently do not have multi-thread support, while OS/2 and AIX 4.1 do.) Second, a server object, derived from the SOMDServer class, provides methods used to manage objects in the server process. Third, one or more class libraries provide object implementations. Usually these libraries are constructed as dynamically linked libraries (DLLs), so they can be loaded and linked by a server program dynamically.
In this simple example, we can use the default DSOM server program, which is already compiled and linked. The default server behaves as a simple server, in that it simply receives and executes requests continuously. The default server creates its server object from the class, SOMDServer. The default server will load any class libraries it needs upon demand.
The "Stack" class library, "stack.dll", can be used without modification in the distributed application. This is possible because the "Stack" class is "well formed"; in other words, there are no methods that implicitly assume the client and the object are in the same address space.
Thus, by using the default server and the existing class library, a simple "Stack" server can be provided without any additional programming!
An application may require more functionality in the server program or the server object than the default implementations provide. A discussion on how to implement server programs and server objects is found later in this chapter, in section 6.4, "Basic Server Programming".