The operation of the FCLOSE intrinsic as used with unlabeled magnetic tape is
outlined in the flowchart of Figure 6-1 “Using the FCLOSE Intrinsic with Unlabeled Magnetic Tape ”.
Note that a tape closed with the temporary no-rewind disposition is
rewound and unloaded if certain additional conditions are not met. It is
possible for a single process to open a magnetic tape device using the device
class option of HPFOPEN/FOPEN, then again open the already-allocated device by
specifying its logical device number (ldev) using the device name option of
HPFOPEN/FOPEN. This may be done in such a manner that both magnetic tape files
are open concurrently. The second HPFOPEN/FOPEN does not require any operator
intervention to allocate the device. When file open and file close calls are
arranged in a nested fashion, tape files may be closed without deallocating the
physical device, as follows:
----
| HPFOPEN allocated tape
| ----
| | HPFOPEN
| | FCLOSE
| ----
| tape remains allocated
| ----
| | FOPEN
| | FCLOSE
| ----
| FCLOSE deallocated tape
----
|
Such nesting of HPFOPEN/FOPEN and FCLOSE pairs is required to keep from rewinding a tape closed
with FCLOSE. A tape closed with the temporary, no-rewind disposition is
rewound and unloaded unless the process closing it has another file currently
open on the device.
When a temporary no-rewind tape is deallocated, the file system has not placed
an EOF (end-of-file mark) at the end of the data file.
The FCLOSE intrinsic can be used to maintain position when creating or reading
a labeled tape file that is part of a volume set. If you close the file with a
disposition code of 0 or 3, the tape does not rewind, but remains positioned at
the next file. If you close the file with a disposition code of 2, the tape
rewinds to the beginning of the file, but is not unloaded. A subsequent
request to open the file does not reposition the tape if the sequence (seq)
subparameter is NEXT or default (1). A disposition code of 1 (save permanent)
implies the close of an entire tape volume set.
Printable version
