2 Connecting The Server

Chapter Index

General Procedure

2.1 General Procedure

The API for the SCF server connection is defined in DataConnection class. This is a singleton, and its shared instance can be obtained with getInstance() static method. DataConnection can have only one connection to the SCF server at a time. The class is used by all underlying services, such as the naming service and the data acquisition service.

The connection can be in three possible states: connected, disconnected, and pending. The pending status is used during transitions between two others statuses. The connection process can take a while, because before the server gets connected, it sends a request to the Kerberos Module on the client side to reads the user's ticket. DataConnection class monitors the communications and can automatically restore the link if it gets broken on some lower level (e.g., because of a network failure). If the server can not be reached for a certain period of time, the connection is closed. Thus, even if the server is not available on-line, the status can be connected until a timeout expires. The naming service requires the server to be on-line: all remote naming requests will block otherwise, or will fail if the server is disconnected. However, the data acquisition service does not require on-line communications at all: event if the status is disconnected, you can manipulate jobs and settings (of course, without getting any actual data...) DataConnection is invariant to the server name: if there is a connection to the server A and a bunch of data acquisition jobs running on it, you can disconnect A and connect another server B, without stopping and loosing these jobs. All the necessary information will be moved between A and B automatically.

Besides connecting the server, this class is used to enable and disable settings, and register JobStatusListeners.

There are several means to control the connection.

From a program, connect() and disconnect() methods can be used to open and close the connection; enableSettings() and disableSettings() enables and disables setting data to the data acquisition system.

For Application Framework, in the classes like JControlsFrame you can have a connection button similar to that for DAE. The button opens a connection dialog. The current SCF server name is defined by scf.server.name application property. The default and an actual user's values are stored in the property database on the server.

The SCF connection dialog can be set up in few steps:

In the application property file (one per application), disable DAE connection support:
```
dae.enabled=0
```
In order to open an SCF connection automatically during the application startup, add one more line:
```
scf.connect=1
```
In the XML frame descriptors (one per frame) set a new status bar ID in the root frame element:
```
<frame statusBarID="ScfStatusBar">
```

The SCF connection dialog can also be opened through Tools|SCF Connection menu item.