SNAX/HLS Application Programming Manual

Life Cycle of a Session
Sessions
3–6 104707 Tandem Computers Incorporated
Partner Data or Other Event—Partner data or other event messages reflect some
message or event associated with the systems operator or partner. They are
identified by a data type, explained later in this section.
If a RECEIVE–DATA verb is used, then in all three cases the top element is removed
from the receive data queue and delivered to the application. If, however, the
RECEIVE–CONTROL–WAIT verb is used, this is true only in the first two cases. If
partner data (or an other event) arrives, the completion of the
RECEIVE–CONTROL–WAIT verb serves as a notification of this event and the data
can then be retrieved with a subsequent RECEIVE–DATA verb. This mechanism
permits the application to be able to await the arrival of large amounts of data without
requiring large amounts of physical memory while the verb is outstanding.
Some of the possible responses occur only if the RDT PROFILE attributes enable them,
such as SSCP text, bind data, and so on.
The HLS–RESPOND verb is used to acknowledge the receipt of previously received
partner data. It allows you to send either positive or negative responses. A PROFILE
attribute must be enabled to use this function or SNAX/HLS generates responses on
your behalf.
Status Requests SNAX/HLS supports verbs that control the flow of traffic on the session. The
SEND–STATUS verb sends SNA sense data to the partner using the LU status
(LUSTAT) message. The REQUEST–SEND–STATE verb can be used on half–duplex
flows to request the right to send data. It can also be used to send an SNA signal
request, single code (%H0001) on sessions that are not half–duplex or are already in
the SEND state, if the PROFILE attribute FORCE–RTS is set.
The PREPARE–TO–CLOSE verb is used to initiate orderly termination of data traffic in
anticipation of session closure. The HLS–FLOW–CONTROL verb sends message and
transaction flow control messages. Finally, the RECEIVE–CONTROL verb is provided
to allow applications to check for messages and other events without actually
dequeuing partner data.
Receive Type Verbs There are three receive–type verbs that are part of SNAX/HLS: the RECEIVE–DATA,
RECEIVE–CONTROL and RECEIVE–CONTROL–WAIT verbs. The RECEIVE–DATA
verb always dequeues the top element of the receive queue for the session and delivers
it to the application. The RECEIVE–CONTROL and RECEIVE–CONTROL–WAIT
verbs allow the application to check for messages and other events without
dequeueing partner data.