Pathway/iTS TCP and Terminal Programming Guide

TCP SETMODE Functions and CONTROL
Operations
Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001
9-4
CONTROL 26 Defined
CONTROL 26 Defined
CONTROL 26 is a CONTROL file system procedure call that allows nonprivileged
processes to cooperate with one another in bringing about the orderly termination of
outstanding read operations.
When an IDS requester is communicating with an FEP that supports the use of
CONTROL 26, the two processes use CONTROL 26 calls and the appropriate responses
jointly to terminate execution of the underlying read operation with no loss of data or
context. As used within the Pathway environment, the general format of a CONTROL
26 procedure call is as follows:
fnum
identifies the file to the FEP.
parameter
= 1 triggers an initialization sequence.
= 300 specifies that a CONTROL 26 request is to be issued to the FEP and that both
the original read and the CONTROL 26 must be completed within five minutes (300
seconds).
tag
is an optional tag field.
In the rest of this section, the phrase CONTROL 26,1 refers to a CONTROL 26 call
whose parameter field contains the value 1, while the phrase CONTROL 26,300
refers to a CONTROL 26 call whose parameter field contains the value 300.
How CONTROL 26 Works
Essentially, the TCP uses CONTROL 26 as follows. When a timeout or escape on
unsolicited message occurs, the TCP issues a CONTROL 26 call to the FEP that is
responsible for completing the read. That process then has up to five minutes (300
seconds) to do any of the following:
•
Complete the outstanding read by sending the requested data (return code = 0)
•
Complete the outstanding read by specifying that it has no data to send (return code
= 187)
•
Complete the outstanding read by specifying that something wrong has happened
that compromises the integrity of subsequent data (return code = 188)
CONTROL ( fnum
, 26
, parameter
, tag ) ;