flock unix

boggy

Thanks ;)

1256 dni temu

BRIRLNOTO
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Hello
I've just registered to say your site is very useful and nicely done!
Thank you very much for your work.

Cheers!

Sorry for offtopic.

1260 dni temu

rhethej
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1279 dni temu

MilkaJunkies
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Who enjoys,
Decided to buy a product in shope but they take a pay E-CHECK
Who benefited from this scheme? It is safe?
You must have your bank account?

1285 dni temu

redbusystone
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water watch joke go dog dog

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Meowmeowz
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Теперь этот форум принадлежит мне. Все вопросы и предложения рассматриваются в icq 477345812

1311 dni temu

Meowmeowz
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Теперь этот форум принадлежит мне. Все вопросы и предложения рассматриваются в icq 477345812

1312 dni temu

anonymous
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How to force only one Unix Perl, Python or Ruby script to be running at a time ?

Let’s say you have the script that is executed every minute via cron. Most likely you’ve tested it, whether it is executing in less than one minute or not, but have you tested it while your box CPU resources are consumed at 100% ? Have you tested it how long it will be executing when your system is swapping ?

What if it will be running longer than the scheduled time interval is ? Then you’re likely to hit CPU, memory, number of processes or other resource’s limits.

Such issues can happen, and if your scripts are not immune to such situations, they’ll act just like nails in your system’s coffin. Especially if they’re running with low priority ( like “nice -n 19 ./your_script.sh” for example ).

Securing scripts that way could also be needed, when more then one execution at a time could have bad influence on information consistency - it may be needed to have such executions atomic.

Here are some code examples of how the scripts could be secured. Those examples are showing the trick to lock the script file itself.

For Perl scripts :

#!/usr/bin/perl
use Fcntl qw(:flock);

open SELF, “< $0″ or die;

flock SELF, LOCK_EX | LOCK_NB or exit;

For Python scripts :

#!/usr/local/bin/python
import fcntl
import sys

f = open(sys.argv[0], ‘r+’)
try:
fcntl.flock(f.fileno(),fcntl.LOCK_EX|fcntl.LOCK_NB)
except IOError:
sys.exit(0)

For Ruby scripts :

#!/usr/local/bin/ruby

f = File.open($0, File::RDONLY)
f.flock File::LOCK_EX | File::LOCK_NB or exit

Those snippets are showing the technique of creating exclusive lock on the script file itself. If another instance is trying to obtain that lock, it is not getting it and exits the execution. After the script quits, the lock is released.

You can just place similar code in the beginning of your script to not let it to run more than once at a time.

1661 dni temu

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