Python fcntl.LOCK_NB Examples

def lock(self):
        if self.handle is None or self.handle.closed:
            self.handle = open(self.path, "w+")
            self.fd = self.handle.fileno()
        if (self.flags & fcntl.LOCK_NB) != 0 or self.seconds is None:
            try:
                fcntl.flock(self.handle, self.flags)
            except IOError as e:
                if e.errno not in [errno.EACCES, errno.EAGAIN]:
                    raise e
                raise Locked(self.path)
        else:
            with timeout(self.seconds):
                try:
                    fcntl.flock(self.handle, self.flags)
                except IOError as e:
                    errnos = [errno.EINTR, errno.EACCES, errno.EAGAIN]
                    if e.errno not in errnos:
                        raise e
                    raise Timeout(self.path) 

def write_pidfile(pid, pidfile):
    """
    This method writes the PID to the pidfile and locks it while the process is running.

    :param pid: PID of SmartHomeNG
    :param pidfile: Name of the pidfile to write to
    :type pid: int
    :type pidfile: str
    """

    fd = open(pidfile, 'w+')
    fd.write("%s" % pid)
    fd.close()

    # lock pidfile:
    try:
        fd = os.open(pidfile, os.O_RDONLY)
        fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        # don't close fd or lock is gone
    except OSError as e:
        print("Could not lock pid file: %d (%s)" % (e.errno, e.strerror) , file=sys.stderr) 

def udpate_status(status_file_path, module_data, module):
	lock_file_path = "{}.lock".format(status_file_path)
	while True:
		status_file_lock = open(lock_file_path, 'r')
		try:
			fcntl.flock(status_file_lock, fcntl.LOCK_EX | fcntl.LOCK_NB)
			with open(status_file_path, "r+") as status_file:
				data = json.load(status_file)
				status_file.seek(0)
				data[module].update(module_data)
				json.dump(data, status_file)
			fcntl.flock(status_file_lock, fcntl.LOCK_UN)
			return
		except:
			time.sleep(0.1)
		status_file_lock.close() 

def load(self):
        # Try to obtain exclusive access to the journal cache
        filename = join(config.app_dir, 'replay.jsonl')
        try:
            try:
                # Try to open existing file
                self.replayfile = open(filename, 'r+', buffering=1)
            except:
                if exists(filename):
                    raise	# Couldn't open existing file
                else:
                    self.replayfile = open(filename, 'w+', buffering=1)	# Create file
            if sys.platform != 'win32':	# open for writing is automatically exclusive on Windows
                lockf(self.replayfile, LOCK_EX|LOCK_NB)
        except:
            if __debug__: print_exc()
            if self.replayfile:
                self.replayfile.close()
            self.replayfile = None
            return False
        self.replaylog = [line.strip() for line in self.replayfile]
        return True 

def containers(self, *args):
        log.info(" ".join(args))
        data = Run(data=True)(deimos.docker.docker("ps", "--no-trunc", "-q"))
        mesos_ids = []
        for line in data.splitlines():
            cid = line.strip()
            state = deimos.state.State(self.state_root, docker_id=cid)
            if not state.exists():
                continue
            try:
                state.lock("wait", LOCK_SH | LOCK_NB)
            except deimos.flock.Err:     # LOCK_EX held, so launch() is running
                mesos_ids += [state.mesos_container_id()]
        containers = Containers()
        for mesos_id in mesos_ids:
            container = containers.containers.add()
            container.value = mesos_id
        recordio.writeProto(containers)
        return 0 

def __init__(self, client_name):
        self.lockfile = os.path.join(get_cache_dir("client_locks"), client_name)
        logger.debug("SingleInstance lockfile: " + self.lockfile)
        if sys.platform == 'win32':
            try:
                # file already exists, we try to remove (in case previous execution was interrupted)
                if os.path.exists(self.lockfile):
                    os.unlink(self.lockfile)
                    self.fd = os.open(self.lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR)
            except OSError as e:
                if e.errno == 13:
                    logger.error("Another instance is already running, quitting.")
                    sys.exit(-1)
                else:
                    raise e
        else:  # non Windows
            self.fp = open(self.lockfile, 'w')
            try:
                fcntl.lockf(self.fp, fcntl.LOCK_EX | fcntl.LOCK_NB)
            except IOError:
                logger.error("Another instance is already running, quitting.")
                sys.exit(-1) 

def __init__(self, path, flags, seconds=default_timeout):
        """Construct a lockable file handle. Handles are recycled.

        If seconds is 0, LOCK_NB will be set. If LOCK_NB is set, seconds will
        be set to 0. If seconds is None, there will be no timeout; but flags
        will not be adjusted in any way.
        """
        full = os.path.abspath(path)
        flags, seconds = nb_seconds(flags, seconds)
        if full not in locks:
            _Struct.__init__(self, path=full,
                                   handle=None,
                                   fd=None,
                                   flags=flags,
                                   seconds=seconds)
            locks[self.path] = self 

def write_pid(path):
    """Writes our PID to *path*."""
    try:
        pid = os.getpid()
        with io.open(path, mode='w', encoding='utf-8') as pidfile:
            # Get a non-blocking exclusive lock
            fcntl.flock(pidfile.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
            pidfile.seek(0)
            pidfile.truncate(0)
            pidfile.write(unicode(pid))
    except:
        logging.error(_("Could not write PID file: %s") % path)
        raise # This raises the original exception
    finally:
        try:
            pidfile.close()
        except:
            pass 

def singleton(lockfile, text="semaphore"):
    """
    Open a lockfile exclusively.
    """

    if not lockfile.parent.exists():
        mkdir(lockfile.parent)

    try:
        if has_fcntl:
            f = open(lockfile, "w")
            fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
        else:
            if lockfile.exists():
                lockfile.unlink()
            fd = os.open(lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR)
            f = open(fd, "w")
        f.write(text)
    except IOError:
        return None
    return f 

def lock(self):
        """
        Locks the package to avoid concurrent operations on its shared
        resources.
        Currently, the only resource shared among scripts executed from
        different directories is the repository.
        """
        if not self.locking_enabled:
            LOG.debug("This package has no shared resources to lock")
            return

        LOG.debug("Checking for lock on file {}.".format(self.lock_file_path))
        self.lock_file = open(self.lock_file_path, "w")
        try:
            fcntl.lockf(self.lock_file, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except IOError as exc:
            RESOURCE_UNAVAILABLE_ERROR = 11
            if exc.errno == RESOURCE_UNAVAILABLE_ERROR:
                LOG.info("Waiting for other process to finish operations "
                         "on {}.".format(self.name))
            else:
                raise
        fcntl.lockf(self.lock_file, fcntl.LOCK_EX) 

def _create_pid_file():
    global fp
    pidfile = CONF.etc.pidfile
    if pidfile is None:
        raise UpdaterErr("No pidfile option found in config file.")
    try:
        fp = open(pidfile, 'w')
        # LOCK_EX    /* exclusive lock */
        # LOCK_NB   * don't block when locking */
        fcntl.flock(fp, fcntl.LOCK_EX | fcntl.LOCK_NB)
        fp.truncate()
        pid = os.getpid()
        fp.write(str(pid))
        fp.flush()
    except Exception as e:
        raise UpdaterErr("Failed to lock pidfile, perhaps named_updater is already running.") 

def test_bounce_lock(self):
        import fcntl

        lock_name = "the_internet"
        lock_file = "/var/lock/%s.lock" % lock_name
        fake_fd = mock.mock_open()
        with mock.patch("builtins.open", fake_fd, autospec=None) as open_patch:
            with mock.patch("fcntl.lockf", autospec=None) as lockf_patch:
                with mock.patch("os.remove", autospec=None) as remove_patch:
                    with bounce_lib.bounce_lock(lock_name):
                        pass
        open_patch.assert_called_once_with(lock_file, "w")
        lockf_patch.assert_called_once_with(
            fake_fd.return_value, fcntl.LOCK_EX | fcntl.LOCK_NB
        )
        fake_fd.return_value.__exit__.assert_called_once_with(None, None, None)
        remove_patch.assert_called_once_with(lock_file) 

def bounce_lock(name):
    """Acquire a bounce lockfile for the name given. The name should generally
    be the service namespace being bounced.

    This is a contextmanager. Please use it via 'with bounce_lock(name):'.

    :param name: The lock name to acquire"""
    lockfile = "/var/lock/%s.lock" % name
    with open(lockfile, "w") as fd:
        remove = False
        try:
            fcntl.lockf(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
            remove = True
            yield
        except IOError:
            raise LockHeldException("Service %s is already being bounced!" % name)
        finally:
            if remove:
                os.remove(lockfile) 

def AcquireFileLock(target_file, flags):
  """ Lock the target file. Note that if |target_file| is closed, the lock is
    automatically released.
  Args:
    target_file: file handle of the file to acquire lock.
    flags: can be any of the type LOCK_EX, LOCK_SH, LOCK_NB, or a bitwise
      OR combination of flags.
  """
  assert flags in (
      LOCK_EX, LOCK_SH, LOCK_NB, LOCK_EX | LOCK_NB, LOCK_SH | LOCK_NB)
  if os.name == 'nt':
    _LockImplWin(target_file, flags)
  elif os.name == 'posix':
    _LockImplPosix(target_file, flags)
  else:
    raise NotImplementedError('%s is not supported' % os.name) 

def AcquireFileLock(target_file, flags):
  """ Lock the target file. Note that if |target_file| is closed, the lock is
    automatically released.
  Args:
    target_file: file handle of the file to acquire lock.
    flags: can be any of the type LOCK_EX, LOCK_SH, LOCK_NB, or a bitwise
      OR combination of flags.
  """
  assert flags in (
      LOCK_EX, LOCK_SH, LOCK_NB, LOCK_EX | LOCK_NB, LOCK_SH | LOCK_NB)
  if os.name == 'nt':
    _LockImplWin(target_file, flags)
  elif os.name == 'posix':
    _LockImplPosix(target_file, flags)
  else:
    raise NotImplementedError('%s is not supported' % os.name) 

def AcquireFileLock(target_file, flags):
  """ Lock the target file. Note that if |target_file| is closed, the lock is
    automatically released.
  Args:
    target_file: file handle of the file to acquire lock.
    flags: can be any of the type LOCK_EX, LOCK_SH, LOCK_NB, or a bitwise
      OR combination of flags.
  """
  assert flags in (
      LOCK_EX, LOCK_SH, LOCK_NB, LOCK_EX | LOCK_NB, LOCK_SH | LOCK_NB)
  if os.name == 'nt':
    _LockImplWin(target_file, flags)
  elif os.name == 'posix':
    _LockImplPosix(target_file, flags)
  else:
    raise NotImplementedError('%s is not supported' % os.name) 

def __enter__(self):
        if self.path is None:
            return self.pidfile

        self.pidfile = open(self.path, "a+")
        try:
            fcntl.flock(self.pidfile.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
        except IOError:
            self.pidfile = None
            raise SystemExit("Already running according to " + self.path)
        self.pidfile.seek(0)
        self.pidfile.truncate()
        self.pidfile.write(str(os.getpid()))
        self.pidfile.flush()
        self.pidfile.seek(0)
        return self.pidfile 

def acquire(self, blocking=None):
        # Give an opportunity to set blocking with the class for context use
        if blocking is None:
            blocking = self.blocking

        if blocking:
            lock_mode = fcntl.LOCK_EX
        else:
            lock_mode = fcntl.LOCK_EX | fcntl.LOCK_NB
        if self.lock_file.closed:
            self._get_lock_file_handle()
        if not self.locked:
            try:
                self.lock = fcntl.flock(self.lock_file, lock_mode)
                self.locked = True
            except IOError:
                raise IOError("File '{}' is already locked.".format(self.lock_file_name))
        else:
            raise IOError("File '{}' is already locked.".format(self.lock_file_name)) 

def write_pid_file(pid_file, pid):
    import fcntl
    import stat

    try:
        fd = os.open(pid_file, os.O_RDWR | os.O_CREAT,
                     stat.S_IRUSR | stat.S_IWUSR)
    except OSError as e:
        shell.print_exception(e)
        return -1
    flags = fcntl.fcntl(fd, fcntl.F_GETFD)
    assert flags != -1
    flags |= fcntl.FD_CLOEXEC
    r = fcntl.fcntl(fd, fcntl.F_SETFD, flags)
    assert r != -1
    # There is no platform independent way to implement fcntl(fd, F_SETLK, &fl)
    # via fcntl.fcntl. So use lockf instead
    try:
        fcntl.lockf(fd, fcntl.LOCK_EX | fcntl.LOCK_NB, 0, 0, os.SEEK_SET)
    except IOError:
        r = os.read(fd, 32)
        if r:
            logging.error('already started at pid %s' % common.to_str(r))
        else:
            logging.error('already started')
        os.close(fd)
        return -1
    os.ftruncate(fd, 0)
    os.write(fd, common.to_bytes(str(pid)))
    return 0 

def open_with_flock(*args, **kwargs):
    """ Context manager for opening file with an exclusive lock. """
    f = open(*args, **kwargs)
    try:
        fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
    except IOError:
        no_attempt = 0
        while no_attempt < MAX_ATTEMPTS:
            try:
                logging.info("Can't immediately write-lock the file ({0}), waiting.".format(f.name))
                start_time = time.time()
                fcntl.lockf(f, fcntl.LOCK_EX)
                break
            except IOError as e:
                if e.errno == errno.EDEADLK:
                    logging.warn("The OS complained because the process have been waiting on the lockf for {0} sec with the error ({1}: {2}). Retrying. ".format(time.time() - start_time, e.errno, e.strerror))
                    f.close()
                    time.sleep(TIME_BETWEEN_ATTEMPTS)
                    f = open(*args, **kwargs)
                    no_attempt += 1
                else:
                    raise e

        if no_attempt == MAX_ATTEMPTS:
            raise IOError("Failed to lock {0} {1} times.".format(f.name, MAX_ATTEMPTS))

    try:
        yield f
    finally:
        fcntl.lockf(f, fcntl.LOCK_UN)
        f.close() 

def __enter__(self):
        """Enter RunSingleInstance class
        :return: self
        """
        self.__checked = True

        try:
            self.__filelock = open(self.__lockfile, 'w+')
            # None blocking lock
            fcntl.lockf(self.__filelock, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except IOError:
            if self.__filelock is not None:
                self.__is_running = True
        return self 

def check_sh_is_running(pidfile):
    """
    This method checks whether another smarthome process process is already running.

    :param pidfile: Name of the pidfile to check
    :type pidfile: str

    :return: True: if SmartHomeNG is running, False: if SmartHome is not running
    :rtype: bool
    """

    pid = read_pidfile(pidfile)
    isRunning = False
    if pid > 0 and psutil.pid_exists(pid):
        try:
            fd = os.open(pidfile, os.O_RDONLY)
            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
            # pidfile not locked, so sh is terminated
        except OSError as e:
            if (e.errno == errno.EWOULDBLOCK):
                # pidfile is locked, so sh is running
                isRunning = True
            else:
                print("Error while testing lock in pidfile %s: %d (%s)" % (pidfile, e.errno, e.strerror) , file=sys.stderr)
                sys.exit(1)
        finally:
            if fd:
                os.close(fd)
    return isRunning 

def _flock(self, fileno):
        fcntl.flock(self.fh.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB) 

def write_pid_file(pid_file, pid):
    import fcntl
    import stat

    try:
        fd = os.open(pid_file, os.O_RDWR | os.O_CREAT,
                     stat.S_IRUSR | stat.S_IWUSR)
    except OSError as e:
        shell.print_exception(e)
        return -1
    flags = fcntl.fcntl(fd, fcntl.F_GETFD)
    assert flags != -1
    flags |= fcntl.FD_CLOEXEC
    r = fcntl.fcntl(fd, fcntl.F_SETFD, flags)
    assert r != -1
    # There is no platform independent way to implement fcntl(fd, F_SETLK, &fl)
    # via fcntl.fcntl. So use lockf instead
    try:
        fcntl.lockf(fd, fcntl.LOCK_EX | fcntl.LOCK_NB, 0, 0, os.SEEK_SET)
    except IOError:
        r = os.read(fd, 32)
        if r:
            logging.error('already started at pid %s' % common.to_str(r))
        else:
            logging.error('already started')
        os.close(fd)
        return -1
    os.ftruncate(fd, 0)
    os.write(fd, common.to_bytes(str(pid)))
    return 0 

def get_gcs_client(self) -> luigi.contrib.gcs.GCSClient:
        if (not os.path.isfile(self.discover_cache_local_path)):
            with open(self.discover_cache_local_path, "w") as f:
                try:
                    fcntl.flock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)

                    params = {"api": "storage", "apiVersion": "v1"}
                    discovery_http = build_http()
                    for discovery_url in (self._DISCOVERY_URI, self._V2_DISCOVERY_URI):
                        requested_url = uritemplate.expand(discovery_url, params)
                        try:
                            content = _retrieve_discovery_doc(
                                requested_url, discovery_http, False
                            )
                        except HttpError as e:
                            if e.resp.status == http_client.NOT_FOUND:
                                continue
                            else:
                                raise e
                        break
                    f.write(content)
                    fcntl.flock(f, fcntl.LOCK_UN)
                except IOError:
                    # try to read
                    pass

        with open(self.discover_cache_local_path, "r") as f:
            fcntl.flock(f, fcntl.LOCK_SH)
            descriptor = f.read()
            fcntl.flock(f, fcntl.LOCK_UN)
            return luigi.contrib.gcs.GCSClient(oauth_credentials=self._load_oauth_credentials(), descriptor=descriptor) 

def _acquire(self):
        open_mode = os.O_RDWR | os.O_CREAT | os.O_TRUNC
        fd = os.open(self._lock_file, open_mode)

        try:
            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except (IOError, OSError):
            os.close(fd)
        else:
            self._lock_file_fd = fd
        return None 

def flock_exclusive():
    ''' lock so only one snapshot of current config is running '''
    fd = os.open(cfg['lock_file'], os.O_CREAT | os.O_TRUNC | os.O_WRONLY, 0600)
    try:
        fcntl.lockf(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
    except IOError:
        return False
    return fd 

def _lock_file(f, dotlock=True):
    """Lock file f using lockf and dot locking."""
    dotlock_done = False
    try:
        if fcntl:
            try:
                fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
            except OSError as e:
                if e.errno in (errno.EAGAIN, errno.EACCES, errno.EROFS):
                    raise ExternalClashError('lockf: lock unavailable: %s' %
                                             f.name)
                else:
                    raise
        if dotlock:
            try:
                pre_lock = _create_temporary(f.name + '.lock')
                pre_lock.close()
            except OSError as e:
                if e.errno in (errno.EACCES, errno.EROFS):
                    return  # Without write access, just skip dotlocking.
                else:
                    raise
            try:
                if hasattr(os, 'link'):
                    os.link(pre_lock.name, f.name + '.lock')
                    dotlock_done = True
                    os.unlink(pre_lock.name)
                else:
                    os.rename(pre_lock.name, f.name + '.lock')
                    dotlock_done = True
            except FileExistsError:
                os.remove(pre_lock.name)
                raise ExternalClashError('dot lock unavailable: %s' %
                                         f.name)
    except:
        if fcntl:
            fcntl.lockf(f, fcntl.LOCK_UN)
        if dotlock_done:
            os.remove(f.name + '.lock')
        raise 

def obtain_lock(lock_filepath):
    """ Open and obtain a flock on the parameter. Returns a file if successful, None if not
    """
    lock_file = open(lock_filepath, "w")
    try:
        fcntl.flock(lock_file, fcntl.LOCK_EX | fcntl.LOCK_NB)
        return lock_file
    except IOError as err:
        if err.errno != errno.EAGAIN:
            raise
        lock_file.close()
        return None 

def acquire_lock_or_exit(self, wait_for_seconds=10):
        lock_file = self.STATE_DIR + '/.iptables.lock'
        i = 0
        f = open(lock_file, 'w+')
        while i < wait_for_seconds:
            try:
                fcntl.flock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
                return
            except IOError:
                i += 1
                time.sleep(1)
        Iptables.module.fail_json(msg="Could not acquire lock to continue execution! "
                                      "Probably another instance of this module is running.")

    # Check if a table has anything to flush (to check all tables pass table='*').