ZIY

The first ZIY implemented on NT was similar to its predecessors in that it was an application program with a GUI interface meant for a human user, generaly someone in the metrology group. Following the model of most Win32 programs, the ZIY was an event driven program. It consisted of a collection of ZY clients, each running in its own thread, each responsible for communications with one corresponding ZY server. The GUI portion of the program, in response to user input, generates an event and places it into the main ZIY event input queue. The ZIY (also running in a separate thread) then takes the event from the queue and processes it, often sending one or more commands to one or more ZYs. When the ZYs process the commands, they send responses to the ZY client objects on the ZIY. These in turn process the data, and if necessary place an event in the GUI event queue. The GUI then displays the data, error messages, status of ZY etc. The GUI portion of the program and the rest of the ZIY thus communicated exclusively through these two message queues. Data in the event objects placed in these queues never included pointers. Thus, tere was a natural ``tear point'' between the GUI portion and the rest of the ZIY. Eventually the ZIY program was divided along this tear point to provide the ZIY with a binary program interface, with the GUI portion becoming the Metrology Group's ZIY Client. To the end user, there is no difference in operation of the system. Now, however, the ZIY Client can be the Metrology GUI client, or it can be an M&C Manager, or anything else. As currently implemented, the ZIY is an NT service. A service is a program that runs on NT independent of any user. The NT Service Manager starts a service soon after boot up, and the service continues to run until the Service Manager ends it, or the computer is shut down. The ZIY service runs at a higher priority level than the default used for user programs, so a logged on user will have little adverse effect on the service.