NAME

SYNOPSIS

  use No::Worries::PidFile qw(*);

  # idiomatic daemon code
  pf_set($pidfile);
  while (1) {
      ...
      $action = pf_check($pidfile);
      last if $action eq "quit";
      pf_touch($pidfile);
      ...
  }
  pf_unset($pidfile);

  # idiomatic daemon code with sleeping
  pf_set($pidfile);
  while (1) {
      ...
      pf_sleep($pidfile, time => 5) or last;
      ...
  }
  pf_unset($pidfile);

  # here is how to handle a --status option
  if ($Option{status}) {
      ($status, $message, $code) = pf_status($pidfile, freshness => 10);
      printf("myprog %s\n", $message);
      exit($code);
  }

  # here is how to handle a --quit option
  if ($Option{quit}) {
      pf_quit($pidfile,
          linger   => 10,
          callback => sub { printf("myprog %s\n", $_[0]) },
      );
  }

DESCRIPTION

The pid file usually contains the process id on a single line, followed by a newline. However, it can also be followed by an optional action, also followed by a newline. This allows some kind of inter-process communication: a process using pf_quit() will append the "quit" action to the pid file and the owning process will detect this via pf_check().

All the functions properly handle concurrency. For instance, when two processes start at the exact same time and call pf_set(), only one will succeed and the other one will get an error.

Since an existing pid file will make pf_set() fail, it is very important to remove the pid file in all situations, including errors. The recommended way to do so is to use an END block:

  # we need to know about transient processes
  use No::Worries::Proc qw();
  # we need to record what needs to be cleaned up
  our(%NeedsCleanup);
  # we set the pid file here and remember to clean it up
  pf_set($pidfile);
  $NeedsCleanup{pidfile} = 1;
  # ... anything can happen here ...
  # cleanup code in an END block
  END {
      # transient processes do not need cleanup
      return if $No::Worries::Proc::Transient;
      # cleanup the pid file if needed
      pf_unset($pidfile) if $NeedsCleanup{pidfile};
  }

FUNCTIONS

pf_set(PATH[, OPTIONS])

set the pid file by writing the given pid at the given path; supported options:

pf_check(PATH[, OPTIONS])

check the pid file and make sure the given pid is present, also return the action in the pid file or the empty string; supported options:

pf_unset(PATH)

unset the pid file by removing the given path

pf_touch(PATH)

touch the pid file (i.e. update the file modification time) to show that the owning process is alive

pf_sleep(PATH[, OPTIONS])

check and touch the pid file and eventually sleep for the givent amount of time, returning true if the program should continue or false if it has been told to stop via pf_quit(); supported options:

pf_status(PATH[, OPTIONS])

use information from the pid file (including its last modification time) to guess the status of the corresponding process, return the status (true means that the process seems to be running); in list context, also return an informative message and an LSB compatible exit code; supported options:

pf_quit(PATH[, OPTIONS])

tell the process corresponding to the pid file to quit (setting its action to "quit"), wait a bit to check that it indeed stopped and kill it using No::Worries::Proc's proc_terminate() if everything else fails; supported options:

SEE ALSO

AUTHOR

Copyright (C) CERN 2012-2019