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# This program is copyright 2008-2011 Percona Inc.
# Feedback and improvements are welcome.
#
# THIS PROGRAM IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
# WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
# MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
#
# This program is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation, version 2; OR the Perl Artistic License. On UNIX and similar
# systems, you can issue `man perlgpl' or `man perlartistic' to read these
# licenses.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc., 59 Temple
# Place, Suite 330, Boston, MA 02111-1307 USA.
# ###########################################################################
# Daemon package
# ###########################################################################
{
# Package: Daemon
# Daemon daemonizes the caller and handles daemon-related tasks like PID files.
package Daemon;
use strict;
use warnings FATAL => 'all';
use English qw(-no_match_vars);
use constant PTDEBUG => $ENV{PTDEBUG} || 0;
use POSIX qw(setsid);
# The required o arg is an OptionParser object.
sub new {
my ( $class, %args ) = @_;
foreach my $arg ( qw(o) ) {
die "I need a $arg argument" unless $args{$arg};
}
my $o = $args{o};
my $self = {
o => $o,
log_file => $o->has('log') ? $o->get('log') : undef,
PID_file => $o->has('pid') ? $o->get('pid') : undef,
};
# undef because we can't call like $self->check_PID_file() yet.
check_PID_file(undef, $self->{PID_file});
PTDEBUG && _d('Daemonized child will log to', $self->{log_file});
return bless $self, $class;
}
sub daemonize {
my ( $self ) = @_;
PTDEBUG && _d('About to fork and daemonize');
defined (my $pid = fork()) or die "Cannot fork: $OS_ERROR";
if ( $pid ) {
PTDEBUG && _d('Parent PID', $PID, 'exiting after forking child PID',$pid);
exit;
}
# I'm daemonized now.
PTDEBUG && _d('Daemonizing child PID', $PID);
$self->{PID_owner} = $PID;
$self->{child} = 1;
POSIX::setsid() or die "Cannot start a new session: $OS_ERROR";
chdir '/' or die "Cannot chdir to /: $OS_ERROR";
$self->_make_PID_file();
$OUTPUT_AUTOFLUSH = 1;
# We used to only reopen STDIN to /dev/null if it's a tty because
# otherwise it may be a pipe, in which case we didn't want to break
# it. However, Perl -t is not reliable. This is true and false on
# various boxes even when the same code is ran, or it depends on if
# the code is ran via cron, Jenkins, etc. Since there should be no
# sane reason to `foo | pt-tool --daemonize` for a tool that reads
# STDIN, we now just always close STDIN.
PTDEBUG && _d('Redirecting STDIN to /dev/null');
close STDIN;
open STDIN, '/dev/null'
or die "Cannot reopen STDIN to /dev/null: $OS_ERROR";
if ( $self->{log_file} ) {
PTDEBUG && _d('Redirecting STDOUT and STDERR to', $self->{log_file});
close STDOUT;
open STDOUT, '>>', $self->{log_file}
or die "Cannot open log file $self->{log_file}: $OS_ERROR";
# If we don't close STDERR explicitly, then prove Daemon.t fails
# because STDERR gets written before STDOUT even though we print
# to STDOUT first in the tests. I don't know why, but it's probably
# best that we just explicitly close all fds before reopening them.
close STDERR;
open STDERR, ">&STDOUT"
or die "Cannot dupe STDERR to STDOUT: $OS_ERROR";
}
else {
if ( -t STDOUT ) {
PTDEBUG && _d('No log file and STDOUT is a terminal;',
'redirecting to /dev/null');
close STDOUT;
open STDOUT, '>', '/dev/null'
or die "Cannot reopen STDOUT to /dev/null: $OS_ERROR";
}
if ( -t STDERR ) {
PTDEBUG && _d('No log file and STDERR is a terminal;',
'redirecting to /dev/null');
close STDERR;
open STDERR, '>', '/dev/null'
or die "Cannot reopen STDERR to /dev/null: $OS_ERROR";
}
}
return;
}
# The file arg is optional. It's used when new() calls this sub
# because $self hasn't been created yet.
sub check_PID_file {
my ( $self, $file ) = @_;
my $PID_file = $self ? $self->{PID_file} : $file;
PTDEBUG && _d('Checking PID file', $PID_file);
if ( $PID_file && -f $PID_file ) {
my $pid;
eval { chomp($pid = `cat $PID_file`); };
die "Cannot cat $PID_file: $OS_ERROR" if $EVAL_ERROR;
PTDEBUG && _d('PID file exists; it contains PID', $pid);
if ( $pid ) {
my $pid_is_alive = kill 0, $pid;
if ( $pid_is_alive ) {
die "The PID file $PID_file already exists "
. " and the PID that it contains, $pid, is running";
}
else {
warn "Overwriting PID file $PID_file because the PID that it "
. "contains, $pid, is not running";
}
}
else {
# Be safe and die if we can't check that a process is
# or is not already running.
die "The PID file $PID_file already exists but it does not "
. "contain a PID";
}
}
else {
PTDEBUG && _d('No PID file');
}
return;
}
# Call this for non-daemonized scripts to make a PID file.
sub make_PID_file {
my ( $self ) = @_;
if ( exists $self->{child} ) {
die "Do not call Daemon::make_PID_file() for daemonized scripts";
}
$self->_make_PID_file();
# This causes the PID file to be auto-removed when this obj is destroyed.
$self->{PID_owner} = $PID;
return;
}
# Do not call this sub directly. For daemonized scripts, it's called
# automatically from daemonize() if there's a --pid opt. For non-daemonized
# scripts, call make_PID_file().
sub _make_PID_file {
my ( $self ) = @_;
my $PID_file = $self->{PID_file};
if ( !$PID_file ) {
PTDEBUG && _d('No PID file to create');
return;
}
# We checked this in new() but we'll double check here.
$self->check_PID_file();
open my $PID_FH, '>', $PID_file
or die "Cannot open PID file $PID_file: $OS_ERROR";
print $PID_FH $PID
or die "Cannot print to PID file $PID_file: $OS_ERROR";
close $PID_FH
or die "Cannot close PID file $PID_file: $OS_ERROR";
PTDEBUG && _d('Created PID file:', $self->{PID_file});
return;
}
sub _remove_PID_file {
my ( $self ) = @_;
if ( $self->{PID_file} && -f $self->{PID_file} ) {
unlink $self->{PID_file}
or warn "Cannot remove PID file $self->{PID_file}: $OS_ERROR";
PTDEBUG && _d('Removed PID file');
}
else {
PTDEBUG && _d('No PID to remove');
}
return;
}
sub DESTROY {
my ( $self ) = @_;
# Remove the PID file only if we created it. There's two cases where
# it might be removed wrongly. 1) When the obj first daemonizes itself,
# the parent's copy of the obj will call this sub when it exits. We
# don't remove it then because the child that continues to run won't
# have it. 2) When daemonized code forks its children get copies of
# the Daemon obj which will also call this sub when they exit. We
# don't remove it then because the daemonized parent code won't have it.
# This trick works because $self->{PID_owner}=$PID is set once to the
# owner's $PID then this value is copied on fork. But the "== $PID"
# here is the forked copy's PID which won't match the owner's PID.
$self->_remove_PID_file() if ($self->{PID_owner} || 0) == $PID;
return;
}
sub _d {
my ($package, undef, $line) = caller 0;
@_ = map { (my $temp = $_) =~ s/\n/\n# /g; $temp; }
map { defined $_ ? $_ : 'undef' }
@_;
print STDERR "# $package:$line $PID ", join(' ', @_), "\n";
}
1;
}
# ###########################################################################
# End Daemon package
# ###########################################################################
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