Paranoid::Lockfile(3pm) User Contributed Perl Documentation Paranoid::Lockfile(3pm)NAME
Paranoid::Lockfile - Paranoid Lockfile support
VERSION
$Id: Lockfile.pm,v 0.65 2011/12/08 07:53:07 acorliss Exp $
SYNOPSIS
use Paranoid::Lockfile;
$rv = plock($lockfile);
$rv = punlock($lockfile);
$rv = pcloseLockfile($lockfile);
DESCRIPTION
This modules provides a relatively safe locking mechanism across multiple processes. This does not work over NFS or across remote systems,
this is only intended for use on a single system at a time, and only on those that support flock.
sysopen is used to avoid race conditions with multiple process attempting to create the same file simultaneously.
SUBROUTINES /METHODS
plock
$rv = plock($filename);
This function attempts to safely create or open the lockfile. It uses sysopen with O_CREAT | O_EXCL to avoid race conditions with other
processes. Returns a true if successful.
Your can pass an optional second argument which would be a string of either 'write' or 'shared'. The default is 'write', which locks the
file in exclusive write mode.
You can pass an optional third argument which would be the lockfile filesystem permissions if the file is created. The default is 0600.
NOTE: This function will block until the advisory lock is granted.
punlock
$rv = punlock($filename);
This function removes any existing locks on the specified filename using flock. If no previous lock existed or it was successful it
returns true. This does not, however, close the open filehandle to the lockfile.
pcloseLockfile
$rv = pcloseLockfile($filename);
This function releases any existing locks and closes the open filehandle to the lockfile. Returns true if the file isn't currently open or
the operation succeeds.
DEPENDENCIES
o Fcntl
o Paranoid
o Paranoid::Debug
BUGS AND LIMITATIONS AUTHOR
Arthur Corliss (corliss@digitalmages.com)
LICENSE AND COPYRIGHT
This software is licensed under the same terms as Perl, itself. Please see http://dev.perl.org/licenses/ for more information.
(c) 2005, Arthur Corliss (corliss@digitalmages.com)
perl v5.14.2 2011-12-08 Paranoid::Lockfile(3pm)
Check Out this Related Man Page
lockfile-progs(1) Lockfile programs lockfile-progs(1)NAME
lockfile-progs - command-line programs to safely lock and unlock files and mailboxes (via liblockfile).
SYNOPSIS
mail-lock [--use-pid] [--retry retry-count]
mail-unlock
mail-touchlock [--oneshot]
lockfile-create [--use-pid] [--retry retry-count] [--lock-name] filename
lockfile-remove [--lock-name] filename
lockfile-touch [--oneshot] [--lock-name] filename
lockfile-check [--use-pid] [--lock-name] filename
DESCRIPTION
Lockfile-progs provides a set a programs that can be used to lock and unlock mailboxes and files safely (via liblockfile):
mail-lock - lock the current user's mailbox
mail-unlock - unlock the current user's mailbox
mail-touchlock - touch the lock on the current user's mailbox
lockfile-create - lock a given file
lockfile-remove - remove the lock on a given file
lockfile-touch - touch the lock on a given file
lockfile-check - check the lock on a given file
By default, the filename argument refers to the name of the file to be locked, and the name of the lockfile will be filename .lock. How-
ever, if the --lock-name argument is specified, then filename will be taken as the name of the lockfile itself.
Each of the mail locking commands attempts to lock /var/spool/mail/<user>, where <user> is the name associated with the effective user ID,
as determined by via geteuid(2).
Once a file is locked, the lock must be touched at least once every five minutes or the lock will be considered stale, and subsequent lock
attempts will succeed. Also see the --use-pid option and the lockfile_create(3) manpage.
The lockfile-check command tests whether or not a valid lock already exists.
OPTIONS -q, --quiet
Suppress any output. Success or failure will only be indicated by the exit status.
-v, --verbose
Enable diagnostic output.
-l, --lock-name
Do not append .lock to the filename. This option applies to lockfile-create, lockfile-remove, lockfile-touch, or lockfile-check.
-p, --use-pid
Write the parent process id (PPID) to the lockfile whenever a lockfile is created, and use that pid when checking a lock's validity.
See the lockfile_create(3) manpage for more information. This option applies to lockfile-create and lockfile-check. NOTE: this option
will not work correctly between machines sharing a filesystem.
-o, --oneshot
Touch the lock and exit immediately. This option applies to lockfile-touch and mail-touchlock. When not provided, these commands will
run forever, touching the lock once every minute until killed.
-r retry-count, --retry retry-count
Try to lock filename retry-count times before giving up. Each attempt will be delayed a bit longer than the last (in 5 second incre-
ments) until reaching a maximum delay of one minute between retries. If retry-count is unspecified, the default is 9 which will give
up after 180 seconds (3 minutes) if all 9 lock attempts fail.
EXAMPLES
Locking a file during a lengthy process:
lockfile-create /some/file
lockfile-touch /some/file &
# Save the PID of the lockfile-touch process
BADGER="$!"
do-something-important-with /some/file
kill "${BADGER}"
lockfile-remove /some/file
EXIT STATUS
0
For lockfile-check this indicates that a valid lock exists, otherwise it just indicates successful program execution.
Not 0
For lockfile-check a non-zero exit status indicates that the specified lock does not exist or is not valid. For other programs it
indicates that some problem was encountered.
SEE ALSO maillock(3)touchlock(3)mailunlock(3)lockfile_create(3)lockfile_remove(3)lockfile_touch(3)lockfile_check(3)AUTHOR
Written by Rob Browning <rlb@defaultvalue.org>
0.1.12 2008-02-10 lockfile-progs(1)