[ANN] lockfile-1.4.1


A

Ara.T.Howard

URLS

http://rubyforge.org/projects/codeforpeople/
http://codeforpeople.com/lib/ruby/lockfile/

SYNOPSIS

lib/lockfile.rb : a ruby library for creating NFS safe lockfiles

bin/rlock : ruby command line tool which uses this library to create lockfiles
and to run arbitrary commands while holding them.

for example

rlock lockfile -- cp -r huge/ huge.bak/

run 'rlock -h' for more info

INSTALL

sudo ruby install.rb


BASIC ALGORITHIM

* create a globally uniq filename in the same filesystem as the desired
lockfile - this can be nfs mounted

* link(2) this file to the desired lockfile, ignore all errors

* stat the uniq filename and desired lockfile to determine is they are the
same, use only stat.rdev and stat.ino - ignore stat.nlink as NFS can cause
this report incorrect values

* iff same, you have lock. either return or run optional code block with
optional refresher thread keeping lockfile fresh during execution of code
block, ensuring that the lockfile is removed..

* iff not same try again a few times in rapid succession (poll), then, iff
this fails, sleep using incremental backoff time. optionally remove
lockfile if it is older than a certain time, timeout if more than a certain
amount of time has passed attempting to lock file.


BASIC USAGE

1)
lockfile = Lockfile.new 'file.lock'
begin
lockfile.lock
p 42
ensure
lockfile.unlock
end


2)
require 'pstore' # which is NOT nfs safe on it's own

opts = { # the keys can be symbols or strings

:retries => nil, # we will try forever to aquire the lock

:sleep_inc => 2, # we will sleep 2 seconds longer than the
# previous sleep after each retry, cycling from
# min_sleep upto max_sleep downto min_sleep upto
# max_sleep, etc., etc.

:min_sleep => 2, # we will never sleep less than 2 seconds

:max_sleep => 32, # we will never sleep longer than 32 seconds

:max_age => 1024, # we will blow away any files found to be older
# than this (lockfile.thief? #=> true)

:suspend => 64, # iff we steal the lock from someone else - wait
# this long to give them a chance to realize it

:refresh => 8, # we will spawn a bg thread that touches file
# every 8 sec. this thread also causes a
# StolenLockError to be thrown if the lock
# disappears from under us - note that the
# 'detection' rate is limited to the refresh
# interval - this is a race condition

:timeout => nil, # we will wait forever

:poll_retries => 16, # the initial attempt to grab a lock is done in a
# polling fashion, this number controls how many
# times this is done - the total polling attempts
# are considered ONE actual attempt (see retries
# above)

:poll_max_sleep => 0.08, # when polling a very brief sleep is issued
# between attempts, this is the upper limit of
# that sleep timeout

:dont_clean => false, # normally a finalizer is defined to clean up
# after lockfiles, settin this to true prevents this

:dont_sweep => false, # normally locking causes a sweep to be made. a
# sweep removes any old tmp files created by
# processes of this host only which are no
# longer alive

:debug => true, # trace execution step on stdout
}

pstore = PStore.new 'file.db'
lockfile = Lockfile.new 'file.db.lock', opts
lockfile.lock do
pstore.transaction do
pstore[:last_update_time] = Time.now
end
end

3) same as 1 above - Lockfile.new takes a block and ensures unlock is called

Lockfile.new('file.lock') do
p 42
end

4) watch locking algorithim in action (debugging only)

Lockfile.debug = true
Lockfile.new('file.lock') do
p 42
end

you can also set debugging via the ENV var LOCKFILE_DEBUG, eg.

~ > LOCKFILE_DEBUG=true rlock lockfile

5) simplified interface : no lockfile object required

Lockfile('lock', :retries => 0) do
puts 'only one instance running!'
end


SAMPLES

* see samples/a.rb
* see samples/nfsstore.rb
* see samples/lock.sh
* see bin/rlock

AUTHOR

Ara T. Howard

EMAIL

(e-mail address removed)

BUGS

bugno > 1 && bugno < 42

HISTORY

1.4.1:
- Mike Kasick <[email protected]> reported a bug whereby false/nil
values for options were ignored. patched to address this bug
- added Lockfile method for high level interface sans lockfile object
- updated rlock program to allow nil/true/false values passed on command
line. eg

rlock --max_age=nil lockfile -- date --iso-8601=seconds

enjoy.

-a
 
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B

Bil Kleb

Ara.T.Howard said:
SYNOPSIS

lib/lockfile.rb : a ruby library for creating NFS safe lockfiles

Can this be used to get around a broken NFS lock configuration
like I have on our branch's cluster?

Later,
 
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M

Michael P. Soulier

Can this be used to get around a broken NFS lock configuration
like I have on our branch's cluster?

I didn't think that locking on nfs was ever really all that safe. I've
seen it fail too often.

Mike
 

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