Shared Files and Folders
Shared Files and Folders Allow multiple, simultaneous user of applications
Normally, applications on an AppleShare server volume can only be used by
one user at a time. When an application is launched, the Finder checks the
shared bit and the file attributes. The file attributes are used to
determine if the the file is locked, etc., and the shared bit is used to
determine if the launch can proceed even if the file ( application) is already in
use (locked bit set, etc.).
Part of the reason why applications are not automatically sharable is based on
the Operating System, as well as database-like tasks. Even so, it was never
designed to perform multi-user database tasks.
If more than one user opened the same resource file at the same time, and one
of them had write access to the file and modified the resource, it would
possibly corrupt files on disk. If both users had write access to the file and
wrote to the file, an invalid resource file is almost a certainty. Although you
is no way for another user to get a fresh copy of the map in memory if the file
changes.
What this all means is that you should not set the shared bit in your
application unless you know that it will never write to itself on disk. Apple has
several rules to make sure your application is multi-user friendly.
• Make sure your application does not create temporary files with fixed
names in a fixed place (such as the directory containing the application).
• Make sure your application is aware that it may be in a multi-user
environment. For instance, make sure that it works correctly if a volume
containing an existing document is on a locked volume. Make sure to check
By setting the shared bit, you are promising that your application will
work 100% correctly if it is launched by more than one user.
There are several differences to note between AppleShare 2.0.1 and File
Sharing. File Sharing allows both folders and volumes to be shared over a
network. This is done via the Finder's Sharing dialog. Access privileges for the
shared folders can be set by the local user.
To allow applications to see shared folders, bit definitions have been added to
sought about a folder. The figure below shows ioFlAttrib for folders as
Note: These bits are READ-ONLY for folders. Do not try to set them with
PBSetCatInfo. As noted in Inside Macintosh, Volume VI,
PBCatSearch searches only on bits 0 and 4. The additional bits
File Sharing supports a user access privilege called blank access privileges. A
folder with blank user access privileges ignores the other access privilege
bits and uses the access privileges of its parent. This is the default mode for
folders in a shared area. Volumes that support blank access privileges have the
bHasBlankAccessPrivileges bit set in the vMAttrib field in the
Folders with blank access privileges can be identified by calling
PBHGetDirAccess. Use PBHSetDirAccess to set blank access privileges
for a folder.
Note: Only the blank access privileges bit in the high byte of ioACAccess may
be set while calling PBHSetDirAccess. The blank access privilege bit is not
Referenced by (2):