MPE/iX Intrinsics Reference Manual (32650-90875)

126 Chapter5
Command Definitions (FCONTROL - FLOCK)
FCONTROL
Only valid for terminal and message files. Only affects the next read if the
file is being read from the terminal; it must be reissued for each read. If
this code is applied to a message file,
item specifies the length of time that
a process waits when reading from an empty file or writing to a full one
and the timeout remains enabled until it is explicitly cancelled.
During block mode reads, the timer halts when a DC2 character is
received. At this time, the block mode read timer is activated by the
system; its values are not user changeable.
5/U16 Reposition file at its beginning:
The next record, read or written, is the first record in the file. Not valid for
files accessed as append-only. On a labeled magnetic tape file or serial disk
file, the tape is positioned at the beginning of the opened file, and not
necessarily at the beginning of the volume. Rejected for spooled DATA
tapes.
Item is ignored.
This
itemnum is supported for byte stream files and all types of directories.
(KSAM) The file is repositioned to the first logical record; the record with
the lowest value in the current key.
6/U16 Write end-of-file:
Marks the end-of-file (EOF) on disk or magnetic tape and is effective only
for those devices:
• If used for a disk file it writes a logical end-of-data marker where the
file was last accessed. The disk file label is updated and written to disk.
• If used for a file residing on unlabeled magnetic tape, a tape mark is
written at that current position.
• If used for message files, it verifies the state of the file by writing the
file label and buffer area to disk; ensures the message file can survive
system crashes. No EOF is written.
• If used for KSAM files, it performs the function of
itemnum =2 and
writes the file label. This guarantees that the end-of-file is correct and
the extent bit map is updated.
Rejected for spooled DATA tapes and labeled magnetic tape files.
Item is ignored.
This
itemnum is supported for byte stream files. It is not applicable to
directories since applications are not permitted to write to directory files.
7/U16 Space forward to tape mark:
Moves a magnetic tape forward until a tape mark is encountered. If used
on labeled magnetic tapes, the tape is positioned at the beginning of user
trailer labels, if any. Rejected for spooled DATA tapes.
Item is ignored.