SNAX/HLS Application Programming Manual

HLS-OPEN Verb
SNAX/HLS Verbs
5–32 104707 Tandem Computers Incorporated
HLS-OPEN Verb The HLS–OPEN verb is used to make sure that the resource that was allocated in a
previous HLS–ALLOCATE verb is now ready for traffic. This operation performs the
SNA operations of INIT–SELF or BIND, and STSN and SDT as required by the session
rules.
If the session is already open, the request is accepted and completed immediately.
This is the only way in which this request with COMPLETION–MODE is I can
complete with RC–OK.
A session can have more than one opener. This typically happens when multiple
applications are using pipelined LUs. When multiple HLS–OPENs are pending for one
session, all open requests complete when the session becomes active.
Application programs that attempt to reestablish a session using HLS–CLOSE and
HLS–OPEN without an intervening HLS–DEALLOCATE and HLS–ALLOCATE
should be aware that HLS–CLOSE does not purge the queue of data awaiting delivery
to the application program. Thus, unless precautions are taken, data received while an
earlier session was in effect may be interpreted as arriving during a new session.
To guard against this phenomenon, you have two choices:
1 Always use HLS–DEALLOCATE and HLS–ALLOCATE. This has the effect of
discarding all the old data and really starting with no prior history.
2 Discard all queued data prior to reopening the session. You can accomplish this
by the following algorithm:
Issue HLS–CLOSE to close the old session.
Loop while RECEIVE–CONTROL indicates data present.
If application data is indicated,
issue RECEIVE–DATA to accept the data
ignore the data
End Loop
Issue HLS–OPEN to initiate a new session