Provided by: libproc-pid-file-perl_1.27-4_all 
NAME
Proc::PID::File - a module to manage process id files
SYNOPSIS
use Proc::PID::File;
die "Already running!" if Proc::PID::File->running();
Process that spawn child processes may want to protect each separately by using multiple
pidfiles.
my $child1 = Proc::PID::File->new(name => "lock.1");
my $child2 = Proc::PID::File->new(name => "lock.2");
which may be checked like this:
<do-something> if $child1->alive();
and should be released manually:
$child1->release();
DESCRIPTION
This Perl module is useful for writers of daemons and other processes that need to tell
whether they are already running, in order to prevent multiple process instances. The
module accomplishes this via *nix-style pidfiles, which are files that store a process
identifier.
The module provides two interfaces: 1) a simple call, and 2) an object-oriented interface
Simple Interface
The simple interface consists of a call as indicated in the first example of the Synopsis
section above. This approach avoids causing race conditions whereby one instance of a
daemon could read the pidfile after a previous instance has read it but before it has had
a chance to write to it.
running [hash[-ref]]
The parameter signature for this function is identical to that of the ->new() method
described below in the OO Interface section of this document. The method's return value is
the same as that of ->alive().
OO Interface
The following methods are provided:
new [hash[-ref]]
This method is used to create an instance object. It automatically calls the ->file()
method described below and receives the same paramters. For a listing of valid keys in
this hash please refer to the aforementioned method documentation below.
In addition to the above, the following constitute valid keys:
verify = 1 | string
This parameter implements the second solution outlined in the WARNING section of this
document and is used to verify that an existing pidfile correctly represents a live
process other than the current. If set to a string, it will be interpreted as a
regular expression and used to search within the name of the running process.
Alternatively, a 1 may be passed: For Linux/FreeBSD, this indicates that the value of
$0 will be used (stripped of its full path); for Cygwin, $^X (stripped of path and
extension) will be used.
If the parameter is not passed, no verification will take place. Please note that
verification will only work for the operating systems listed below and that the OS
will be auto-sensed. See also DEPENDENCIES section below.
Supported platforms: Linux, FreeBSD, Cygwin
debug
Any non-zero value turns debugging output on. Additionally, if a string is passed
containing the character M, the module name will be prefixed to the debugging output.
file [hash[-ref]]
Use this method to set the path of the pidfile. The method receives an optional hash (or
hash reference) with the keys listed below, from which it makes a path of the format:
$dir/$name.pid.
dir Specifies the directory to place the pid file. If left unspecified, defaults to
/var/run.
name
Indicates the name of the current process. When not specified, defaults to
basename($0).
alive
Returns true when the process is already running. Please note that this call must be made
*after* daemonisation i.e. subsequent to the call to fork(). If the verify flag was set
during the instance creation, the process id is verified, alternatively the flag may be
passed directly to this method.
touch
Causes for the current process id to be written to the pidfile.
release
This method is used to delete the pidfile and is automatically called by DESTROY method.
It should thus be unnecessary to call it directly.
locktime [hash[-ref]]
This method returns the mtime of the pidfile.
AUTHOR
Erick Calder <ecalder@cpan.org>
ACKNOWLEDGEMENTS
1k thx to Steven Haryanto <steven@haryan.to> whose package (Proc::RID_File) inspired this
implementation.
Our gratitude also to Alan Ferrency <alan@pair.com> for fingering the boot-up problem and
suggesting possible solutions.
DEPENDENCIES
For Linux, FreeBSD and Cygwin, support of the verify option requires availability of the
ps utility. For Linux/FreeBSD This is typically found in the procps package. Cygwin users
need to run version 1.5.20 or later for this to work.
WARNING
This module may prevent daemons from starting at system boot time. The problem occurs
because the process id written to the pidfile by an instance of the daemon may
coincidentally be reused by another process after a system restart, thus making the daemon
think it's already running.
Some ideas on how to fix this problem are catalogued below, but unfortunately, no
platform-independent solutions have yet been gleaned.
- leaving the pidfile open for the duration of the daemon's life
- checking a "ps" to make sure the pid is what one expects (current implementation)
- looking at /proc/$PID/stat for a process name
- check mtime of the pidfile versus uptime; don't trust old pidfiles
- try to get the script to nuke its pidfile when it exits (this is vulnerable to hardware
resets and hard reboots)
- try to nuke the pidfile at boot time before the script runs; this solution suffers from
a race condition wherein two instances read the pidfile before one manages to lock it,
thus allowing two instances to run simultaneously.
SUPPORT
For help and thank you notes, e-mail the author directly. To report a bug, submit a patch
or add to our wishlist please visit the CPAN bug manager at: http://rt.cpan.org
AVAILABILITY
The latest version of the tarball, RPM and SRPM may always be found at:
http://perl.arix.com/ Additionally the module is available from CPAN.
LICENCE
This utility is free and distributed under GPL, the Gnu Public License. A copy of this
license was included in a file called LICENSE. If for some reason, this file was not
included, please see http://www.gnu.org/licenses/ to obtain a copy of this license.
$Id: File.pm,v 1.16 2004-04-08 02:27:25 ekkis Exp $