# mypidfile.py - functions for properly locking a PIDFile # # Copyright (C) 2010 Arthur de Jong # # This library is free software; you can redistribute it and/or # modify it under the terms of the GNU Lesser General Public # License as published by the Free Software Foundation; either # version 2.1 of the License, or (at your option) any later version. # # This library 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 # Lesser General Public License for more details. # # You should have received a copy of the GNU Lesser General Public # License along with this library; if not, write to the Free Software # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA # 02110-1301 USA import fcntl import errno import os class MyPIDLockFile(object): """Implementation of a PIDFile fit for use with the daemon module that locks the PIDFile with fcntl.lockf().""" def __init__(self, path): self.path = path def __enter__(self): """Lock the PID file and write the process ID to the file.""" fd = os.open(self.path, os.O_RDWR | os.O_CREAT, 0644) try: fcntl.lockf(fd, fcntl.LOCK_EX | fcntl.LOCK_NB) pidfile = os.fdopen(fd, 'w') except: os.close(fd) raise pidfile.write('%d\n' % os.getpid()) pidfile.flush() self.pidfile = pidfile return self def __exit__(self, exc_type, exc_value, traceback): """Release the lock (close the lockfile).""" fcntl.lockf(self.pidfile.fileno(), fcntl.LOCK_UN) self.pidfile.close() del self.pidfile def is_locked(self): """Check whether the file is already present and locked.""" try: fd = os.open(self.path, os.O_RDWR, 0644) # Python doesn't seem to have F_TEST so we'll just try to lock fcntl.lockf(fd, fcntl.LOCK_EX | fcntl.LOCK_NB) # if we're here we must have aquired the lock fcntl.lockf(fd, fcntl.LOCK_UN) return False except (IOError, OSError), e: if e.errno == errno.ENOENT: return False if e.errno in (errno.EACCES, errno.EAGAIN): return True raise finally: if 'fd' in locals(): os.close(fd)