#
# Copyright (c) 2008--2011 Red Hat, Inc.
#
# This software is licensed to you under the GNU General Public License,
# version 2 (GPLv2). There is NO WARRANTY for this software, express or
# implied, including the implied warranties of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. You should have received a copy of GPLv2
# along with this software; if not, see
# http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt.
#
# Red Hat trademarks are not licensed under GPLv2. No permission is
# granted to use or replicate Red Hat trademarks that are incorporated
# in this software or its documentation.
#
import os
import sys
import fcntl
from errno import EWOULDBLOCK, EEXIST
import fcntl
class LockfileLockedException(Exception):
"""thrown ONLY when pid file is locked."""
pass
class Lockfile:
"""class that provides simple access to a PID-style lockfile.
methods: __init__(lockfile), acquire(), and release()
NOTE: currently acquires upon init
The *.pid file will be acquired, or an LockfileLockedException is raised.
"""
def __init__(self, lockfile, pid=None):
"""create (if need be), and acquire lock on lockfile
lockfile example: '/var/run/up2date.pid'
"""
# cleanup the path and assign it.
self.lockfile = os.path.abspath(
os.path.expanduser(
os.path.expandvars(lockfile)))
self.pid = pid
if not self.pid:
self.pid = os.getpid()
# create the directory structure
dirname = os.path.dirname(self.lockfile)
if not os.path.exists(dirname):
try:
os.makedirs(dirname)
except OSError, e:
if hasattr(e, 'errno') and e.errno == EEXIST:
# race condition... dirname exists now.
pass
else:
raise
# open the file -- non-destructive read-write, unless it needs
# to be created XXX: potential race condition upon create?
self.f = os.open(self.lockfile, os.O_RDWR|os.O_CREAT|os.O_SYNC)
self.acquire()
def acquire(self):
"""acquire the lock; else raise LockfileLockedException."""
try:
fcntl.flock(self.f, fcntl.LOCK_EX|fcntl.LOCK_NB)
except IOError, e:
if e.errno == EWOULDBLOCK:
raise LockfileLockedException(
"cannot acquire lock on %s." % self.lockfile), None, sys.exc_info()[2]
else:
raise
# unlock upon exit
fcntl.fcntl(self.f, fcntl.F_SETFD, 1)
# truncate and write the pid
os.ftruncate(self.f, 0)
os.write(self.f, str(self.pid) + '\n')
def release(self):
# Remove the lock file
os.unlink(self.lockfile)
fcntl.flock(self.f, fcntl.LOCK_UN)
os.close(self.f)
def main():
"""test code"""
try:
L = Lockfile('./test.pid')
except LockfileLockedException, e:
sys.stderr.write("%s\n" % e)
sys.exit(-1)
else:
print "lock acquired "
print "...sleeping for 10 seconds"
import time
time.sleep(10)
L.release()
print "lock released "
if __name__ == '__main__':
# test code
sys.exit(main() or 0)