Home > Cannot Lock > Flock



Sometimes this kind of interference can be exploited. So the TERM signal there may or may not work all the time. NFSv2 has two atomic operations: symlink rename With NFSv3 the create call is also atomic. You can also add an author to your watch list by going to a thread that the author has posted to and clicking on the "Add this author to my watch

Unfortunately, the specification doesn't make any guarantees that the file will be created securely. But mkdir is pretty nice for less demanding use cases IMO. –akostadinov May 13 '14 at 18:03 You can use Bash’es noclobber option with regular files. –Palec Oct 6 I have run this script for days and never experienced a deadlock, albeit with only 4 simultaneous MATLAB sessions. Wolfgang SourceForge About Site Status @sfnet_ops Powered by Apache Allura™ Find and Develop Software Create a Project Software Directory Top Downloaded Projects Community Blog @sourceforge Resources Help Site Documentation Support Request


Search To add search criteria to your watch list, search for the desired term in the search box. java file cross-platform share|improve this question asked Feb 27 '09 at 16:59 Sébastien RoccaSerra 10.6k63850 add a comment| 7 Answers 7 active oldest votes up vote 21 down vote For Java Locking application variables efficientlyThe need to lock application variables can reduce server performance, because all requests that use Application scope variables must wait on a single lock.

However, if you want all machines sharing files in a network to obey the lock, you need to use a directory that they're sharing; /var/mail is one such location. A query like doc("/db/my/resource.xml")//para returns a result set to the application executing the query. A minor nuisance is that mkstemp(3) doesn't directly support the environment variables TMP or TMPDIR (as discussed below), so if you want to support them you have to add code to If your OS does not support lockfile(1) and your solution has to work on NFS, you have not many options....

Please keep this field empty: Show pagesource Old revisions Backlinks howto/mutex.txt · Last modified: 2015/08/08 17:22 by bill_thomson This site is supported by Performing Databases - your experts for database Github Exit: ${ETXT[ECODE]}($ECODE)" >&2 rm -rf "${LOCKDIR}"' 0 echo "$$" >"${PIDFILE}" # the following handler will exit the script upon receiving these signals # the trap on "0" (EXIT) from above will If it's not, the script can start, updating the PID in the lockfile to its own. http://stackoverflow.com/questions/185451/quick-and-dirty-way-to-ensure-only-one-instance-of-a-shell-script-is-running-at For example, an attacker could create an "old" file, arrange for the tmp cleaner to plan to delete the file, delete the file himself, and run a secure program that creates

Delete on clean exit New runs fail until the issue that caused the unclean exit to be resolved and the lockfile is manually removed. # acquire lock # do work (code The following table shows one scenario that would cause a deadlock: User 1 User 2 Locks the Session scope. Your question in the thread was indeed close to but more restrictive than mine. Almost all network accessed file systems (NFS, SAMBA, etc) have very unreliable (or at least unpredictable) synchronizations on file creates or deletes that make a general Java-ish approach inadvisable.


Subject: locking file access OR exchanging messages bw Matlab Instances From: David Portabella David Portabella (view profile) 3 posts Date: 10 Aug, 2010 18:28:24 Message: 11 of 14 Reply to this click site To prevent this, a form of MUTEX (mutual exclusion) lock is needed. Flock Why aren't interactions between molecules of an ideal gas and walls of container negligible? For proper lock cleanup, you really should set your traps to something like this psuedo code (lifted, simplified and untested but from actively used scripts) : #======================================================================= # Predefined Global Variables

Second, for an XQuery, keeping the lock during the entire operation would often not be feasible. If the link named by the new argument exists, it shall be removed and old renamed to new. Always use the smallest time-out value that does not result in a significant number of time-outs. Cheers. –Mark Stinson Jul 6 '15 at 19:41 Have you tested exit 1002 ? –Gilles Quenot Jan 20 at 21:16 add a comment| up vote 8 down vote Really

Maybe this DIR=$(cd $(dirname "$0"); pwd) exec $DIR/`basename $0` "[email protected]" is a little better Jan Schampera, 2010/05/27 06:34 If no chdir() was made, then a exec "$0" should work fine IMHO. Tagging Messages can be tagged with a relevant label by any signed-in user. Now, P3 is scheduled by OS to run which means it removes the lock dir P2 created (FYI, the last thing P3 did was the kill command) 10. Every document object in eXist has an attached lock object.

This mostly mitigates a potential race condition, but doesn't entirely limit it (though the risk is miniscule). eXist thus allows DIRTY READS during an XQuery (in fact, the query engine will check for existing write locks while executing the doc() function, but it immediately releases any lock it Usage include sh_lock_functions.sh init using sh_lock_init lock using sh_acquire_lock check lock using sh_check_lock unlock using sh_remove_lock Script File sh_lock_functions.sh #!/bin/bash function sh_lock_init { sh_lock_scriptName=$(basename $0) sh_lock_dir="/tmp/${sh_lock_scriptName}.lock" #lock directory sh_lock_file="${sh_lock_dir}/lockPid.txt" #lock file

Some taxonomies call these deadlock, livelock, or locking failure conditions.

ln "$LOCKFILE.$$" "$LOCKFILE" 2>/dev/null; then PID=`head -1 "$LOCKFILE"` if [ -z "$PID" ]; then rm -f "$LOCKFILE" else kill -0 "$PID" 2>/dev/null || rm -f "$LOCKFILE" fi if ! Application All code sections with this attribute in the same application share a single lock. To prevent unnecessary time-outs, lock the minimum amount of code possible. Peled, M.J.

For example, a deadlock would occur if process 1 locks resources A and waits for resource B, while process 2 locks resource B and waits for resource A. Directory operations are NOT atomic under NFSv2 and NFSv3 (please refer to the book 'NFS Illustrated' by Brent Callaghan, ISBN 0-201-32570-5; Brent is a NFS-veteran at Sun). flock: http://www.kernel.org/pub/software/utils/script/flock/ solo: http://timkay.com/solo/ Choose the locking method The best way to set a global lock condition is the UNIX® filesystem. bash usually doesn't treat signals if it waits for a subprocess to end ( actually waits for them to finish and only AFTER that fires up the signal handlers).

Here is how to make it work for sure: lockfile=/var/lock/myscript.lock if ( set -o noclobber; echo "$$" > "$lockfile") 2> /dev/null ; then trap 'rm -f "$lockfile"; exit $?' INT TERM This book will call these sequencing problems.

Interference caused by trusted processes (from the secure program's point of view). Thread To add a thread to your watch list, go to the thread page and click the "Add this thread to my watch list" link at the top of the page. You can't even create the file, close it, and re-open it, even if the permissions limit who can open it.

Tries to lock the Application scope, but the Application scope is already locked by User 2. Seems mkdir is a better solution than set -C; >tempfile if there's any chance you'll be using ksh88 according to the comments there. –Mikel Feb 25 '11 at 2:00 4 Another copy is running or manually lock clean up required." exit 1001 # Or work out some sleep_while_execution_lock elsewhere fi } function rmlock { [[ ! -d $__lockdir ]] \ && With modern releases of NFS, you shouldn't have to worry using either.

Unfortunately, I don't think it will work for me - I run the program under Condor Management system and don't think I can work with databases there. By placing the code that sets all of the related session variables in a single cflock tag, you ensure that all the variables get set together. Using mkdir(2) or link(2) are about the same, at a practical level; I just prefer using hard links because more implementations of NFS allowed atomic hard links than atomic mkdir. First, don't use the technique used by very old Unix C programs, which is calling creat() or its open() equivalent, the open() mode O_WRONLY | O_CREAT | O_TRUNC, with the file