/usr/share/backintime/common/applicationinstance.py is in backintime-common 1.0.8-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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# Copyright (C) 2008-2009 Oprea Dan, Bart de Koning, Richard Bailey
#
# 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; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# 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.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
import os
import os.path
import time
#class used to handle one application instance mechanism
class ApplicationInstance:
#specify the file used to save the application instance pid
def __init__( self, pid_file, auto_exit = True ):
self.pid_file = pid_file
if auto_exit:
if self.check( True ):
self.start_application()
#check if the current application is already running, returns True if this is the application instance
def check( self, auto_exit = False ):
#check if the pidfile exists
if not os.path.isfile( self.pid_file ):
return True
#read the pid from the file
pid = 0
try:
file = open( self.pid_file, 'rt' )
data = file.read()
file.close()
pid = int( data )
except:
pass
#check if the process with specified by pid exists
if 0 == pid:
return True
try:
os.kill( pid, 0 ) #this will raise an exception if the pid is not valid
except:
return True
if auto_exit:
#exit the application
print "The application is already running !"
exit(0) #exit raise an exception so don't put it in a try/except block
return False
#called when the single instance starts to save it's pid
def start_application( self ):
file = open( self.pid_file, 'wt' )
file.write( str( os.getpid() ) )
file.close()
#called when the single instance exit ( remove pid file )
def exit_application( self ):
try:
os.remove( self.pid_file )
except:
pass
if __name__ == '__main__':
#create application instance
app_instance = ApplicationInstance( '/tmp/myapp.pid' )
#do something here
print "Start MyApp"
time.sleep(5) #sleep 5 seconds
print "End MyApp"
#remove pid file
app_instance.exit_application()
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