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python3.6
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rhn
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rhnLockfile.py
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# # Copyright (c) 2008--2016 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 from rhn.i18n import bstr 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 = sys.exc_info()[1] 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: if sys.exc_info()[1].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, bstr(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: sys.stderr.write("%s\n" % sys.exc_info()[1]) 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)