File(3) User Contributed Perl Documentation File(3)NAMEProc::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 $
perl v5.14.0 2009-10-13 File(3)
