LUA Concepts

The Windows LUA for Microsoft SNA Server provides one common API to port applications from various operating environments to Microsoft Windows NT and Windows version 3.x. The LUA verbs (both Request Unit Interface [RUI] and Session Level Interface [SLI]), routines, and information contained in the Microsoft SNA Server SDK represent an evolving Windows LUA that is based on IBM ES for OS/2 version 1.0. The SDK also includes a set of Windows enhancements for application development.

An application accesses the LUA through either the RUI or SLI verbs and routines. Each verb, defined by a structure called the verb control block (VCB), supplies parameters to the LUA, which performs the desired function and returns parameters to the application.

By design, the LUA is asynchronous and uses semaphores for notification messages. While semaphores work extremely well for the Windows NT and OS/2 systems, the Windows enhancements built into the Windows LUA also allow for asynchronous support for Windows version 3.x-based applications in the LUA interface. The Windows LUA provides the following entry points for both RUI and SLI verbs: RUI, SLI, WinRUI, and WinSLI. WinRUI and WinSLI provide asynchronous message notification for all Windows-based RUI and SLI verbs, while RUI and SLI provide support for event notification. Windows 3.x-based applications use WinRUI and WinSLI for asynchronous message notification.

The only Windows extensions required for the Windows LUA are for initialization (WinRUIStartup or WinSLIStartup) and termination (WinRUICleanup or WinSLICleanup) purposes. Depending on your application, other Windows extensions may be useful to you, but are not required.

Several LUA calls and Windows enhancements are of particular importance and should be reviewed before using Microsoft SNA Server: