Guardian Procedure Calls Reference Manual

Table 11 CONTROL Operations 2 Through 27 (continued)
Description of <param>DescriptionOperation
NoneMagnetic tape, force end-of-volume (EOV). Next volume in set
is requested and current volume is unloaded.
24
Valid only for ANSI or IBM label tape.
NoneRequests immediate completion of all outstanding I/O requests
without loss of data by the recipient of the CONTROL 26
request.
26
Wait for DP2 disk file write.27
This operation is not supported for queue files.
This operation finishes when a WRITE, WRITEUPDATE, or
WRITEUPDATEUNLOCK occurs on a DP2 disk file designated
by filenum. Not valid for partitioned files.
Do not assume that the file contains any new data when a call
to CONTROL 27 finishes; assume only that it is time to check
the file for new data.
CONTROL 27 also finishes when a WRITE or WRITEUPDATE
occurs as part of a logical undo of a transaction by the backout
process or when a volume goes down.
If SETMODE function 146 was specified, each write completes
only one CONTROL 27; otherwise each write completes all
pending CONTROL 27 operations.
To ensure that no updates are missed, issue a nowait
CONTROL 27 call on one open to a file, then read data from
the file on another open, and finally wait for the CONTROL
operation to finish. If CONTROL 27 were executed after
reading, a write by another process could occur between the
read and the CONTROL operations. The file open that is used
for the CONTROL operation must have a syncdepth of 0. Path
errors and network errors might indicate successful completion.
See the discussion of CONTROL operation 27 in the Guardian
Programmer's Guide.
1
These values are supported only on unstructured opens of secondary partitions of enhanced key-sequenced files.
Considerations
• Nowait and CONTROL
If the CONTROL procedure is used on a file that is opened nowait, it must be completed with
a call to the AWAITIO procedure.
• Disk files
Writing EOF to an unstructured file
Writing EOF to an unstructured disk file sets the EOF pointer to the relative byte address
indicated by the setting of the next-record pointer and writes the new EOF setting in the
file label on disk. Specifically, write:
◦
end-of-file pointer := next-record pointer;
(File pointer action for CONTROL operation 2, write EOF.)
210 Guardian Procedure Calls (C)