With any POSIX-conforming shell, you can also use:
This works to guarantee that only one process holds the lock (assuming that lockfile is an absolute pathname), but the read could fail if the lock was held at the time you requested the lock but the lock holder terminated before the read was processed. (So, you need to verify that the read worked rather than assume that it will always succeed.)
Hi,
I have written below check lockfile script but need some tweaking on it.
If there is a lockfile from present, I need the script to retry every 10 seconds to see if the lockfile is still there. After 120 seconds it should send an email.
In my current version, if the script encounters... (6 Replies)
Just tried out the following code from "Using lockfiles in shell scripts":
#!/bin/bash
if ; then
echo "File exists"
else
echo "File does not exists. Create file now."
echo 1 > number.txt
fi
lockfile script.lock
a=$(/usr/bin/tail -n 1 number.txt)
if ; then... (1 Reply)
Hi all,
I have to test some user priviliges. The goal is to be sure that an unauthorized user can't restart some modules (ssh, mysql etc...).
I'm trying to automate it with a shell script but in same cases I got the syslog broadcast message.
Is there any way to simply get a return code... (3 Replies)
Hi,
I am new to this forum, could any one please help me to understand the LOCKFILE command with an example and what exactly it is used for and how it is used.
Thanks
Reshu289 (4 Replies)
Hello,
I have been working on using "flock"/file lock to prevent two instances of a bash script from being executed. Below is a simplified version of what I have to illustrate the flock part. It works as it is set up there below however the piece I am trying to figure out is how to get it to... (2 Replies)
I'm changing my mindset from a few big processes moving data from a few sources under an external, dependency-based scheduler to multiple processes moving data from many sources run by each client cron and possibly interfering with each other. It has the benefits of more granular code but I'm... (11 Replies)
Hi i have a script that check pings and i use flock to so the script wont run
multipul times :
its not the whole script but this is the idea :
(
flock -x -w 3 200 || exit 1
/usr/sbin/fping -c$count -i$interval -a $hosts > $FILE1 2>&1
) 200>/var/lock/.myscript.exclusivelock
now i... (4 Replies)
Discussion started by: batchenr
4 Replies
LEARN ABOUT SUSE
thread::semaphore
Thread::Semaphore(3pm) Perl Programmers Reference Guide Thread::Semaphore(3pm)NAME
Thread::Semaphore - Thread-safe semaphores
VERSION
This document describes Thread::Semaphore version 2.09
SYNOPSIS
use Thread::Semaphore;
my $s = Thread::Semaphore->new();
$s->down(); # Also known as the semaphore P operation.
# The guarded section is here
$s->up(); # Also known as the semaphore V operation.
# The default semaphore value is 1
my $s = Thread::Semaphore-new($initial_value);
$s->down($down_value);
$s->up($up_value);
DESCRIPTION
Semaphores provide a mechanism to regulate access to resources. Unlike locks, semaphores aren't tied to particular scalars, and so may be
used to control access to anything you care to use them for.
Semaphores don't limit their values to zero and one, so they can be used to control access to some resource that there may be more than one
of (e.g., filehandles). Increment and decrement amounts aren't fixed at one either, so threads can reserve or return multiple resources at
once.
METHODS
->new()
->new(NUMBER)
"new" creates a new semaphore, and initializes its count to the specified number (which must be an integer). If no number is
specified, the semaphore's count defaults to 1.
->down()
->down(NUMBER)
The "down" method decreases the semaphore's count by the specified number (which must be an integer >= 1), or by one if no number
is specified.
If the semaphore's count would drop below zero, this method will block until such time as the semaphore's count is greater than or
equal to the amount you're "down"ing the semaphore's count by.
This is the semaphore "P operation" (the name derives from the Dutch word "pak", which means "capture" -- the semaphore operations
were named by the late Dijkstra, who was Dutch).
->up()
->up(NUMBER)
The "up" method increases the semaphore's count by the number specified (which must be an integer >= 1), or by one if no number is
specified.
This will unblock any thread that is blocked trying to "down" the semaphore if the "up" raises the semaphore's count above the
amount that the "down" is trying to decrement it by. For example, if three threads are blocked trying to "down" a semaphore by
one, and another thread "up"s the semaphore by two, then two of the blocked threads (which two is indeterminate) will become
unblocked.
This is the semaphore "V operation" (the name derives from the Dutch word "vrij", which means "release").
NOTES
Semaphores created by Thread::Semaphore can be used in both threaded and non-threaded applications. This allows you to write modules and
packages that potentially make use of semaphores, and that will function in either environment.
SEE ALSO
Thread::Semaphore Discussion Forum on CPAN: http://www.cpanforum.com/dist/Thread-Semaphore <http://www.cpanforum.com/dist/Thread-Semaphore>
Annotated POD for Thread::Semaphore: http://annocpan.org/~JDHEDDEN/Thread-Semaphore-2.09/lib/Thread/Semaphore.pm
<http://annocpan.org/~JDHEDDEN/Thread-Semaphore-2.09/lib/Thread/Semaphore.pm>
Source repository: http://code.google.com/p/thread-semaphore/ <http://code.google.com/p/thread-semaphore/>
threads, threads::shared
MAINTAINER
Jerry D. Hedden, <jdhedden AT cpan DOT org>
LICENSE
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl v5.12.1 2010-04-26 Thread::Semaphore(3pm)