GDSX Manual

Design and Development

Extended General Device Support (GDSX) Manual–134303

2-8

System Tasks

Listener Task

This task is created during GDSX process initialization and is always active thereafter.

There is only one listener task per GDSX process, and it is always task number 2.

The kernel forwards all system messages (except BREAK and 3270 status) received by

GDSX to the listener task. The listener task executes an endless loop that processes or

routes system messages such as:

The Listener also acts as an agent for the kernel. When TSCODE receives a request by

means of $RECEIVE, it may be the case that resources required to process the message

(for example, pool space) are not currently available. In such cases, the request is

passed to the Listener, which acquires the missing resources before forwarding the

request to the appropriate task.

The listener task maintains a count of currently active system tasks (including Monitor,

Listener, and Backup if GDSX is running as a process pair). Upon receipt of a system

message that requires a system task to handle it, if five system tasks are active, the

Listener waits until one of the five tasks terminates before initiating the new task.

$RECEIVE is blocked while the Listener is waiting for an available task.

Backup Task

If GDSX is run as a process pair, TSCODE creates a backup task (task 3) during GDSX

primary process initialization, which in turn creates a GDSX backup process and

checkpoints data to the backup process. There is only one backup task per GDSX

process, and it is always active after it is started.

UserInit Task

This task exists temporarily upon startup of a GDSX process.

Netmon Task

When the listener task receives a NETMON system message (CPU UP or CPU DOWN),

this task is created temporarily to oversee the creation of a DOWNCPU task or the

processing of an UPCPU system message.

DownCPU Task

This task exists temporarily during the processing of a DOWNCPU system message.

Open Task

During an open of a line or device this task creates a new DEVICE^HANDLER task or

LINE^HANDLER task and then is deleted.

ABEND

CONTROL

CPU DOWN

CPU RELOAD/UP

DEVICEINFO

NET MONITOR

OPEN

STOP