How SCO Visual Tcl works
The following is a high-level look at what happens when a
user runs a SCO Visual Tcl application:
A user starts an application (also referred to as a client)
written using SCO Visual Tcl, either from the command line (by entering
vtcl progname) or by clicking on the application's icon.
In either case, the vtcl interpreter processes the
vtcl attempts to contact the server process over a guaranteed
connection (named pipe).
If the SCO Visual Tcl server process for the type of display is not
yet running, one starts automatically. For example, if a user at a
character terminal starts an application and cm_vtcld is
not running, the process starts.
The SCO Visual Tcl application (client) makes a connection to the server,
and the server displays the appropriate information on the user's
screen. This information consists of
items such as menus, buttons, and text-entry fields.
The user performs
on these widgets.
An event is an action such as clicking on a button, choosing a menu
item, entering text in a text field, and so on.
For each widget, the programmer defined the possible events in
the application's script. When the user performs the event (such as
pressing a button), a specified
This callback calls a procedure in the application's script,
which can then call additional operating system or Tcl
Additional events and callbacks are performed until the user
exits the program. At that time, the communication channel between
the client and server is dropped, but the server process
remains active until the system shuts down, listening for additional requests.
Basic components of SCO Visual Tcl
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003