No::Worries::PidFile - pid file handling without worries
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", $_[0]) }, ); }
This module eases pid file handling by providing high level functions to set, check, touch and unset pid files. All the functions die() on error.
The pid file usually contains the process id on a single line, followed by a newline. However, it can also be followed by an optional action, also followed by a newline. This allows some kind of inter-process communication: a process using pf_quit() will append the quit action to the pid file and the owning process will detect this via pf_check().
quit
All the functions properly handle concurrency. For instance, when two processes start at the exact same time and call pf_set(), only one will succeed and the other one will get an error.
Since an existing pid file will make pf_set() fail, it is very important to remove the pid file in all situations, including errors. The recommended way to do so is to use an END block:
# we need to know about transient processes use No::Worries::Proc qw(); # we need to record what needs to be cleaned up our(%NeedsCleanup); # we set the pid file here and remember to clean it up pf_set($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}; }
This module provides the following functions (none of them being exported by default):
set the pid file by writing the given pid at the given path; supported options:
pid: the pid to use (default: $$)
pid
$$
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:
unset the pid file by removing the given path
touch the pid file (i.e. update the file modification time) to show that the owning process is alive
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:
time: the time to sleep (default: 1, can be fractional)
time
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:
freshness: maximum age allowed for an active pid file
freshness
timeout: check multiple times until success or timeout
timeout
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:
callback: code that will be called with information to report
callback
linger: maximum time to wait after having told the process to quit (default: 5)
linger
kill: kill specification to use when killing the process
kill
http://refspecs.linuxbase.org/LSB_4.1.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html, No::Worries, No::Worries::Proc.
Lionel Cons http://cern.ch/lionel.cons
Copyright (C) CERN 2012-2019
To install No::Worries, copy and paste the appropriate command in to your terminal.
cpanm
cpanm No::Worries
CPAN shell
perl -MCPAN -e shell install No::Worries
For more information on module installation, please visit the detailed CPAN module installation guide.