HP 3000 Manuals

Accessing Files Programmer's Guide

Closing a Magnetic Tape File 

The operation of the FCLOSE intrinsic as used with unlabeled magnetic
tape is outlined in the flowchart of Figure 6-1 .


          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.

MPE/iX 5.0 Documentation