FTAM/9000 Programmer's Guide

112 Chapter 3
HP FTAM/9000 Data Structures
Ft_concurrency_control
• The ft_open() concurrency control must be identical to—or more
restrictive than—the ft_select() concurrency control; it may not be
less restrictive
CAUTION When a system has an NFS-mounted file system , two different files can
have the same device id and inode number. If both are used by FTAM
concurrently, the locks applied to one file could interfere with a select or
open operation on the other file.
Furthermore, files on NFS-mounted file systems are visible on more than
one host. Therefore, it is possible for FTAM to have locks on the same file
from two different hosts. While each host may believe it has exclusive
access to the file, in fact both hosts have concurrent access.
Table 3-1 Concurrency Control: Default Settings
In the
SELECT
regime:
For actions not set in
the requested_access
parameter,
corresponding locks
default to:
For each action set in
the requested_access
parameter, if the
action is read or
read_attribute, the
corresponding lock
defaults to:
For each action set in
the requested_access
parameter, otherwise,
the corresponding
lock defaults to:
Not Required Shared Exclusive
In the OPEN
regime:
By default, all locks in the OPEN regime are set to the lock value for the
current SELECT regime, either the defaults (above) or user-selected.