We have routers which don't support SNMP OIDs for BGP peer status information, so I wrote a fairly simple script. The API call is relatively 'expensive' so I cache the information and want to implement locking so that only a single process ever updates whilst the others reference the cached data.

Overview:
  if cache's modification time is less than 60 seconds old, or less th
+an 120 seconds old when it's busy being updated {
    load cached hash
  else
    load information via API and save hash to speed up subsequent look
+ ups

[download]
my $cache_ttl = 60;
my $cachefile = '/tmp/mtapi.'.$router.'.cache';
my $lockfile  = '/tmp/mtapi.'.$router.'.lock';
my %bgp_peer;
my $cached = 0;
my $modified = (stat($cachefile))[9];
if (defined $modified) {
  if (($modified >= (time-$cache_ttl)) || ((-e $lockfile) && ($modifie
+d >= (time-($cache_ttl*2))))) {
    if (%bgp_peer = %{lock_retrieve($cachefile)}) { $cached = 1 };
  }
}
if ($cached == 0) {
  open (LOCK, ">$lockfile");
  flock(LOCK, LOCK_EX);
  my $api = MikroTik::API->new (
    {
      host     => $router,
      username => $api_user,
      password => $api_passwd,
      use_ssl  => 1,
    }
  );
  %bgp_peer = $api->get_by_key('/routing/bgp/peer/print', 'name');
  $api->logout();
  lock_nstore \%bgp_peer, $cachefile;
  chmod 0660, $cachefile;
  close LOCK;
  unlink $lockfile;
}

[download]

I however still see concurrent API logins happening, a lot more than the 'one in a million' that I had assumed...

PS: I'm really not a programmer, so I'd humbly accept any recommendations or suggestions.

In reply to Faster locking by bbs2web

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