in reply to Re^2: how many instances are running ?
in thread how many instances are running ?

I'm not talking about lockfiles. I'm talking about using the file locking mechanisms that are built into your operating system. If you get an exclusive lock on a file, then any other process trying to get an exclusive lock on the same file will block until the first lock is released.

--

<http://dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg

Replies are listed 'Best First'.
Re^4: how many instances are running ?
by jeanluca (Deacon) on Mar 06, 2007 at 11:40 UTC
    The locking mechanism seems to require a file that can be locked
    My first attempt resulted in a permission denied :)
    But I'm looking for something like
    #! /usr/bin/perl -lw
use strict;

use Shell qw(ps);

my $sh = Shell->new;
my @pids =  grep ( $_ =~ /t\.pl/, $sh->ps('aux'));
print "list of running instances:\n@pids\n" ;
for( @pids ) {
    exit if ( $_ && /t\.pl\s.*\-a/ ) ;
}
print "no other instance running\n" ;

    [download]
    Which actually seems to work quite good :)

    LuCa
[reply]
[d/l]
      The locking mechanism seems to require a file that can be locked My first attempt resulted in a permission denied :)
      Hmm, can we dig into that little problem, please?

      Many systems only allow you to lock a file (actually a file handle) that you have open for writing. Once that condition is met, it really ought to work.

      Oh, and if you try to lock the file in nonblocking mode, it won't wait but instead report failure to lock. Store that result and you will know whether to output anything, or not.

      BTW I'd prefer to always enable warnings, but let every instance have their own copy for the log file.

[reply]
[reply]

In Section Seekers of Perl Wisdom