File Based Throttling

idsfa has asked for the wisdom of the Perl Monks concerning the following question:

I was challenged (in the CB) to come up with a file based locking mechanism that would solve atcroft's throttling problem. Additionally, I was asked that it

Run on any UNIX
Not leave stale locks if the script dies badly
Not be vulnerable to having lock files deleted
Have no race conditions
Solve world hunger

The following is my best stab. It looks a little too short to be correct ... can anyone see problems (and ideally, solutions)? You may want to cf. LockFile::Simple.

$LOCK = $0;
$MAX_RUNNING = 10;

sub lock_count
{
   return scalar split /\s+/, `fuser $LOCK 2>/dev/null`;
}

die ("Too many running processes")  if (&lock_count >= $MAX_RUNNING);
open(LOCK) or die("Failed to acquire lock");
die ("Too many running processes")  if (&lock_count > $MAX_RUNNING);
[download]

Remember, when you stare long into the abyss, you could have been home eating ice cream.

Comment on File Based Throttling Download Code

Replies are listed 'Best First'.
•Re: File Based Throttling by merlyn (Sage) on Oct 17, 2003 at 16:21 UTC
`[localhost:~] merlyn% fuser fuser: Command not found.` [download] So much for the "any unix" part. {grin} -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply] [d/l]
Re: Re: File Based Throttling by idsfa (Vicar) on Oct 17, 2003 at 16:44 UTC
For the canonical definition of Unix, it's a required utility. atcroft is probably correct about the pathing issue. But then, you already knew that. Remember, when you stare long into the abyss, you could have been home eating ice cream.	[reply]
Re: •Re: File Based Throttling by atcroft (Abbot) on Oct 17, 2003 at 16:32 UTC
My guess is that it may be on the system, but just not in the path. Tried it as well, and on my home linux machine, I found it as /sbin/fuser ; on Solaris 7 and 8 machines I have access to, it was /usr/sbin/fuser. YMMV, however.	[reply]
•Re: Re: •Re: File Based Throttling by merlyn (Sage) on Oct 17, 2003 at 17:46 UTC
Nope, it's nowhere. `[localhost:~] merlyn% man fuser No manual entry for fuser` [download] This is Mac OSX, which is Mach/BSD based, arguably more "unix" than Linux is, because there are parts that were sold under the Unix label, unlike Linux. `fuser` is definitely definitely not-portable. And there's really nothing portable to replace it, either. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply] [d/l]
Re: •Re: File Based Throttling by sweetblood (Prior) on Oct 17, 2003 at 17:11 UTC
Even if you were to find fuser it is usually only available to root.	[reply]
Re: Re: •Re: File Based Throttling by vek (Prior) on Oct 17, 2003 at 21:16 UTC
Even if you were to find fuser it is usually only available to root. Er, that's not strictly true, any user can run `fuser`. I'm just a joe schmo user on a Solaris 9 box: `[vek@alyssa - /home/vek]% fuser -u . .: 2053c(vek) 2017c(vek) 1351c(vek)` [download] -- vek --	[reply] [d/l] [select]