SNAX/HLS Application Programming Manual

Life Cycle of a Session
Sessions
3–4 104707 Tandem Computers Incorporated
In the operation of the OPEN–SESSION verb, ACCEPT and ACQUIRE differences
come into play:
If the PROFILE for the session specifies ACQUIRE open mode, SNAX/HLS
immediately attempt s to contact the session partner. If the application program is
a PLU, a BIND is sent to the SLU session partner. If the application program is a
SLU, an INIT-SELF is sent to the PLU session partner. Thus, in ACQUIRE mode,
the application program essentially tries to directly acquire the session partner.
If the PROFILE for the session specifies ACCEPT open mode, SNAX/HLS queues
the verb, awaiting an invitation to begin the session from the session partner. If
the application program is a PLU, SNAX/HLS awaits a subsequent INIT-SELF
from the session partner. If the application program is a SLU, SNAX/HLS awaits
a a BIND from the session partner.
Simple and Enhanced
Verbs
The enhanced verbs offer the following capabilities, which are not available with the
simple verbs:
Nowait open session actions (when using waited IO). By use of the queued
completion mode, your application need not be idle while awaiting a session open.
Specification of user data. The new verbs enable you to specify the text of the
user–data area provided on the BIND and INIT–SELF records.
Support for 24 byte LUNAME (for remote passthrough.
Data–Transfer Verbs SNAX/HLS supports five verbs that manage the exchange of application data between
session partners: RECEIVE–DATA, RECEIVE–CONTROL–WAIT, SEND–DATA,
SEND–AND–RECEIVE–DATA, and HLS–RESPOND. To understand the operation of
these verbs, you must look at the structure of the work queues within SNAX/HLS.
For each LU managed by SNAX/HLS, there is a receive queue of data and status
messages. Execution of a RECEIVE–DATA verb or of the receive portion of a SEND–
AND–RECEIVE–DATA verb results in the top element of the receive queue being
returned to the user (if the queue is empty, the verb is queued internally by
SNAX/HLS). Note that the receive queue can exist even after the session is terminated
by the session partner. In other words, if the SNAX/HLS user has several messages
on its receive queue and the partner terminates the session, the receive queue is not
flushed. The process can receive all messages before receiving a return code of RC–
SESSION–TERMINATED on a receive–type verb.