Re^2: Faster locking

Thank you! I dropped the .lock file and am now locking the script itself. It appears I can lock it again, with no apparent side effect, if it was locked earlier. Found a neat way of referencing the running script without using DATA but now can't find the site to reference it.

The lock_retrieve and lock_nstore were intended to keep other processes waiting, whilst the updated data is being flushed to the cache file.

Herewith the resulting script snippet:

my $cache_ttl = 60;
my $cachefile = '/tmp/mtapi.'.$router.'.cache';
my %bgp_peer;
my $cached = 0;
my $modified = (stat($cachefile))[9];
open our $lockfile, '<', $0 || die $!;
if (defined $modified) {
  if (($modified >= (time-$cache_ttl)) || (!flock $lockfile, LOCK_EX |
+ LOCK_NB)) {
    if (%bgp_peer = %{lock_retrieve($cachefile)}) { $cached = 1 };
  }
}
if ($cached == 0) {
  if (!flock $lockfile, LOCK_EX | LOCK_NB) { print STDERR "Another pro
+cess is already using MikroTik API.\n"; exit 6 };
  $api->connect();
  $api->login();
  %bgp_peer = $api->get_by_key('/routing/bgp/peer/print', 'name');
  $api->logout();
  lock_nstore \%bgp_peer, $cachefile;
  chmod 0660, $cachefile;
  flock $lockfile, LOCK_UN;
}
[download]

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Re^3: Faster locking by bbs2web (Acolyte) on Apr 04, 2017 at 08:16 UTC
Could someone please confirm that Perl would skip trying to acquire a lock when the first 'if' condition is true? Should I rather place the test in to a nested condition, completely outside of the first? `if ( (1 == 1) \|\| (!flock $lockfile, LOCK_EX \| LOCK_NB) )` PS: Things appear to be working as expected, but I would still like to know, for my own peace of mind.	[reply] [d/l]
Re^4: Faster locking by bbs2web (Acolyte) on Apr 04, 2017 at 08:38 UTC
Okay, so it works as expected: Test code: `#!/usr/bin/perl use strict; use warnings; use Fcntl qw(:flock); open our $lockfile, '<', $0 \|\| die $!; if ( (1 == 1) \|\| (!flock $lockfile, LOCK_EX \| LOCK_NB) ) { print "in loop\n"; sleep 30; if (flock $lockfile, LOCK_EX \| LOCK_NB) { print "locked\n"; } else { print "not locked\n"; } sleep 30; }` [download] First instance: `in loop locked` [download] Second instance: `in loop not locked` [download]	[reply] [d/l] [select]