Configuring Systems for Terminals, Printers, and Other Serial Devices (32022-90051)

Chapter 9 175

Describing Asynchronous Devices

How Devices Are Owned and Why

Devices (terminals, printers, plotters, etc.) are subject to ownership. If a

device is owned by a process, then use of the device by other processes is

restricted. For instance, when a session owns a terminal, only the

process which initiated the session or its child process, can access the

terminal.

To determine which process owns a device, use the MPE/iX SHOWDEV

command. Asynchronous devices will be listed as one of the following:

• Available. The device is not owned. Any process that wants to claim

ownership of the device can do so. For terminals, this means that no

one is logged on to the device or no other process has

programmatically opened the terminal. For printers, it means that

the device is not spooled, nor has it been opened by a user program.

• Unavailable. The device is owned. The owner—a job, a session, or

the system—is also listed.

• Spooled. The device is owned by the spooler while data is being

transferred between a spoolﬁle (on disk) and the device. Other

processes can access the device through the spooler, but only the

spooler process owns the device. Printers and plotters are the only

asynchronous devices that are spooled.

NOTE

UPS devices are always owned by the system.