/usr/share/backintime/common/applicationinstance.py is in backintime-common 1.1.12-1.
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) 2008-2016 Oprea Dan, Bart de Koning, Richard Bailey, Germar Reitze
#
# 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 fcntl
import errno
import logger
class ApplicationInstance:
'''class used to handle one application instance mechanism
pid_file: full path of file used to save pid and procname
auto_exit: automatically call sys.exit if there is an other
instance running
flock: use file-locks to make sure only one instance
is checking at the same time
tests:
test/test_applicationinstance.TestApplicationInstance.test_create_and_remove_pid_file
test/test_applicationinstance.TestApplicationInstance.test_write_pid_file
test/test_applicationinstance.TestApplicationInstance.test_existing_process_with_correct_procname
test/test_applicationinstance.TestApplicationInstance.test_existing_process_with_wrong_procname
test/test_applicationinstance.TestApplicationInstance.test_existing_process_with_wrong_pid
test/test_applicationinstance.TestApplicationInstance.test_killing_existing_process
test/test_applicationinstance.TestApplicationInstance.test_non_existing_process
test/test_applicationinstance.TestApplicationInstance.test_leftover_empty_lockfile
'''
def __init__( self, pid_file, auto_exit = True, flock = False ):
'''specify the file used to save the application instance pid
'''
self.pid_file = pid_file
self.pid = 0
self.procname = ''
self.flock_file = None
if flock:
self.flockExclusiv()
if auto_exit:
if self.check( True ):
self.start_application()
def __del__(self):
'''unlock and clean up
'''
self.flockUnlock()
def check( self, auto_exit = False ):
'''check if the current application is already running
returns True if this is the only application instance
auto_exit: automatically call sys.exit if there is an other
instance running
'''
#check if the pidfile exists
if not os.path.isfile( self.pid_file ):
return True
self.pid, self.procname = self.readPidFile()
#check if the process with specified by pid exists
if 0 == self.pid:
return True
try:
os.kill( self.pid, 0 ) #this will raise an exception if the pid is not valid
except OSError as err:
if err.errno == errno.ESRCH:
#no such process
return True
else:
raise
#check if the process has the same procname
if self.procname and self.procname != self.readProcName(self.pid):
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
def start_application( self ):
'''called when the single instance starts to save it's pid
'''
pid = str(os.getpid())
procname = self.readProcName(pid)
try:
with open( self.pid_file, 'wt' ) as f:
f.write( pid + '\n' + procname )
except OSError as e:
logger.error('Failed to write PID file %s: [%s] %s' %(e.filename, e.errno, e.strerror))
self.flockUnlock()
def exit_application( self ):
'''called when the single instance exit ( remove pid file )
'''
try:
os.remove( self.pid_file )
except:
pass
def flockExclusiv(self):
'''create an exclusive lock to block a second instance while
the first instance is starting.
tests:
test/test_applicationinstance.TestApplicationInstance.test_thread_write_without_flock
test/test_applicationinstance.TestApplicationInstance.test_flock_exclusive
'''
try:
self.flock_file = open(self.pid_file + '.flock', 'w')
fcntl.flock(self.flock_file, fcntl.LOCK_EX)
except OSError as e:
logger.error('Failed to write flock file %s: [%s] %s' %(e.filename, e.errno, e.strerror))
def flockUnlock(self):
'''remove the exclusive lock. Second instance can now continue
but should find it self to be obsolet.
'''
if self.flock_file:
fcntl.fcntl(self.flock_file, fcntl.LOCK_UN)
self.flock_file.close()
try:
os.remove(self.flock_file.name)
except:
#an other instance was faster
#race condition while using 'if os.path.exists(...)'
pass
self.flock_file = None
def readProcName(self, pid):
try:
with open('/proc/%s/cmdline' % pid, 'r') as f:
return f.read().strip('\n')
except OSError as e:
logger.warning('Failed to read process name from %s: [%s] %s' %(e.filename, e.errno, e.strerror))
return ''
def readPidFile(self):
'''read the pid and procname from the file
pid: Process Indicator (int)
'''
pid = 0
procname = ''
try:
with open( self.pid_file, 'rt' ) as f:
data = f.read()
data = data.split('\n', 1)
pid = int(data[0])
if len(data) > 1:
procname = data[1].strip('\n')
except OSError as e:
logger.warning('Failed to read PID and process name from %s: [%s] %s' %(e.filename, e.errno, e.strerror))
except ValueError as e:
logger.warning('Failed to extract PID and process name from %s: %s'
%(self.pid_file, str(e)))
return (pid, procname)
if __name__ == '__main__':
import time
#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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