Python fcntl 模块，LOCK_EX 实例源码

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 do_magic(self):
        if OS_WIN:
            try:
                if os.path.exists(LOCK_PATH):
                    os.unlink(LOCK_PATH)
                self.fh = os.open(LOCK_PATH, os.O_CREAT | os.O_EXCL | os.O_RDWR)
            except EnvironmentError as err:
                if err.errno == 13:
                    self.is_running = True
                else:
                    raise
        else:
            try:
                self.fh = open(LOCK_PATH, 'w')
                fcntl.lockf(self.fh, fcntl.LOCK_EX | fcntl.LOCK_NB)
            except EnvironmentError as err:
                if self.fh is not None:
                    self.is_running = True
                else:
                    raise

def open(self):
        if self.opened:
            return

        self.lock = open(SETTINGS.CACHE_PATH + '.lock', 'ab')
        try:
            fcntl.flock(self.lock, fcntl.LOCK_EX | fcntl.LOCK_NB)
            mode = 'c'
        except IOError:
            logger.warn("Cache locked, using read-only")
            mode = 'r'
            self.lock.close()
            self.lock = None

        try:
            self.storage = shelve.open(SETTINGS.CACHE_PATH, mode)
        except Exception as e:
            if mode != 'c':
                raise
            logger.warn("Dropping corrupted cache on %s", e)
            self.lock.truncate(0)
            self.storage = shelve.open(SETTINGS.CACHE_PATH, mode)
        self.opened = True

def lock_method(lock_filename):
    ''' Use an OS lock such that a method can only be called once at a time. '''

    def decorator(func):

        @functools.wraps(func)
        def lock_and_run_method(*args, **kwargs):

            # Only run this program if it's not already running
            # Snippet based on
            # http://linux.byexamples.com/archives/494/how-can-i-avoid-running-a-python-script-multiple-times-implement-file-locking/
            fp = open(lock_filename, 'w')
            try:
                fcntl.lockf(fp, fcntl.LOCK_EX | fcntl.LOCK_NB)
            except IOError:
                raise SystemExit(
                    "This program is already running.  Please stop the current process or " +
                    "remove " + lock_filename + " to run this script."
                )

            return func(*args, **kwargs)

        return lock_and_run_method

    return decorator

def store(proxys):
    pidfile = open(proxyFilePath, "a")
    for i in range(10):
        try:
            fcntl.flock(pidfile, fcntl.LOCK_EX | fcntl.LOCK_NB)  # LOCK_EX ???:????????????????????????
            # LOCK_NB ????: ?????????????????????????????????????
            if type(proxys) == type([]):
                for proxy in proxys:
                    pidfile.write(proxy + '\n')
            else:
                pidfile.write(proxys + '\n')
            pidfile.close()
            break
        except:
            # print "another instance is running..."
            time.sleep(3)

def push(self, message):
        """ Push a new message. """
        if self.overflow_mode == 'drop':
            if self.max_length > -1 and self.get_length() >= self.max_length:
                return
            if self.max_size > -1 and self.get_size() >= self.max_size:
                return

        with open(self.file_path, 'a') as fd:
            # Let's hold an exclusive lock.
            fcntl.flock(fd, fcntl.LOCK_EX)
            fd.write(message.serialize())
            fcntl.flock(fd, fcntl.LOCK_UN)
            fd.close()

        if self.overflow_mode == 'slide':
            if self.max_size == -1 and self.max_length > -1:
                while self.get_length() > self.max_length:
                    self.shift()
            elif self.max_size > -1 and self.max_length == -1:
                while self.get_size() > self.max_size:
                    self.shift()

def init_list(self, data=None):
        """
        Initialize asid_list file.
        :param data: list or a string
        :return:
        """
        file_path = os.path.join(running_path, '{sid}_list'.format(sid=self.sid))
        if not os.path.exists(file_path):
            if isinstance(data, list):
                with open(file_path, 'w') as f:
                    fcntl.flock(f, fcntl.LOCK_EX)
                    f.write(json.dumps({
                        'sids': {},
                        'total_target_num': len(data),
                    }))
            else:
                with open(file_path, 'w') as f:
                    fcntl.flock(f, fcntl.LOCK_EX)
                    f.write(json.dumps({
                        'sids': {},
                        'total_target_num': 1,
                    }))

def list(self, data=None):
        """
        Update asid_list file.
        :param data: tuple (s_sid, target)
        :return:
        """
        file_path = os.path.join(running_path, '{sid}_list'.format(sid=self.sid))
        if data is None:
            with open(file_path, 'r') as f:
                fcntl.flock(f, fcntl.LOCK_EX)
                result = f.readline()
                return json.loads(result)
        else:
            with open(file_path, 'r+') as f:  # w+ causes a file reading bug
                fcntl.flock(f, fcntl.LOCK_EX)
                result = f.read()
                if result == '':
                    result = {'sids': {}}
                else:
                    result = json.loads(result)
                result['sids'][data[0]] = data[1]
                f.seek(0)
                f.truncate()
                f.write(json.dumps(result))

def lock_path(path, timeout=0):
    fd = os.open(path, os.O_CREAT)
    flags = fcntl.fcntl(fd, fcntl.F_GETFD, 0)
    flags |= fcntl.FD_CLOEXEC
    fcntl.fcntl(fd, fcntl.F_SETFD, flags)

    started = time.time()

    while True:
        try:
            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except IOError:
            if started < time.time() - timeout:
                raise LockError("Couldn't obtain lock")
        else:
            break
        time.sleep(0.1)

    def unlock_path():
        fcntl.flock(fd, fcntl.LOCK_UN)
        os.close(fd)

    return unlock_path

def cache(self,name,suffix=''):
        """Allocate a name in cache, if cache was setup
        also lock the file , so that another process have to wait before using the same file name

        Important: call unlock() on result
        """
        #TODO: something more clever here?
        fname=''
        if self.work_dir is not None:
            fname=self.cache_dir+os.sep+name+suffix
            lock_name=fname+'.lock'
            f=self._locks[lock_name]=open(lock_name, 'a')
            fcntl.lockf(f.fileno(), fcntl.LOCK_EX )
        else:
            fname=self.tmp(name+suffix)

        return fname

def edit_hosts():
    f = os.popen('/usr/local/bin/etcdctl ls --sort --recursive /hosts')
    hosts_str = f.read()


    hosts_arr = hosts_str.strip('\n').split('\n')
    hosts_fd = open('/tmp/hosts', 'w')

    fcntl.flock(hosts_fd.fileno(), fcntl.LOCK_EX)

    hosts_fd.write('127.0.0.1 localhost cluster' + '\n')
    i = 0
    for host_ip in hosts_arr:
        host_ip = host_ip[host_ip.rfind('/') + 1:]
        if host_ip[0] == '0':
            hosts_fd.write(host_ip[1:] + ' cluster-' + str(i) + '\n')
        else:
            hosts_fd.write(host_ip + ' cluster-' + str(i) + '\n')
        i += 1

    hosts_fd.flush()
    os.system('/bin/cp /tmp/hosts /etc/hosts')
    hosts_fd.close()

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 isSingleInstance(flavor_id=""):
    global fp
    basename = os.path.splitext(os.path.abspath(sys.argv[0]))[0].replace(
        "/", "-").replace(":", "").replace("\\", "-") + '-%s' % flavor_id + '.lock'
    lockfile = os.path.normpath(tempfile.gettempdir() + '/' + basename)

    if sys.platform == 'win32':
        try:
            if os.path.exists(lockfile):
                os.unlink(lockfile)
            fp = os.open(
                lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR)
        except OSError:
            return False

    else:  # non Windows
        fp = open(lockfile, 'w')
        try:
            fcntl.lockf(fp, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except IOError:
            return False

    return True

def acquire(self):
        if self.mutex_debug:
            print("I2C mutex acquire")

        acquired = False
        while not acquired:
            try:
                self.DexterLockI2C_handle = open('/run/lock/DexterLockI2C', 'w')
                # lock
                fcntl.lockf(self.DexterLockI2C_handle, fcntl.LOCK_EX | fcntl.LOCK_NB)
                acquired = True
            except IOError: # already locked by a different process
                time.sleep(0.001)
            except Exception as e:
                print(e)

        if self.mutex_debug:
            print("I2C mutex acquired {}".format(time.time()))

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 write_data(self):
        if self.config_newer_than_data():
            self.read_data()
            return False
        else:
            try:
                self.data = {"clouds":self.quads.clouds.data, "hosts":self.quads.hosts.data, "history":self.quads.history.data, "cloud_history":self.quads.cloud_history.data}
                with open(self.config, 'w') as yaml_file:
                    fcntl.flock(yaml_file, fcntl.LOCK_EX | fcntl.LOCK_NB)
                    yaml_file.write(yaml.dump(self.data, default_flow_style=False))
                    fcntl.flock(yaml_file, fcntl.LOCK_UN)
                self.read_data()
                return True
            except Exception, ex:
                self.logger.error("There was a problem with your file %s" % ex)
                return False

def _try_lock():
    """Check and create lock file - prevent running application twice.

    Return lock file handler.
    """
    lock_file_path = _find_config_file("app.lock", False)
    _check_dir_for_file(lock_file_path)
    try:
        if fcntl is not None:
            lock_file = open(lock_file_path, "w")
            fcntl.lockf(lock_file, fcntl.LOCK_EX | fcntl.LOCK_NB)
        else:
            if os.path.isfile(lock_file_path):
                _LOG.error("another instance detected (lock file exists) "
                           "- exiting")
                return None
            lock_file = open(lock_file_path, "w")
        return lock_file
    except IOError as err:
        import errno
        if err.errno == errno.EAGAIN:
            _LOG.error("another instance detected - exiting")
        else:
            _LOG.exception("locking failed: %s", err)
    return None

def getLock(self,lock_path,force=False,timeout=30,filename="easyops.lock"):
        import fcntl
        lockFile = os.path.join(lock_path,filename)
        #fp = open(lockFile,'w')
        try:
            if os.path.isfile(lockFile):
                os.chmod(lockFile, 0o777)
        except:
            pass
        self.fp[lockFile] = open(lockFile,'w')
        count = 0
        while True:
            if count > timeout:
                return False
            count += 1
            try:
                fcntl.flock(self.fp[lockFile],fcntl.LOCK_EX|fcntl.LOCK_NB)
            except IOError:
                if force == True:
                    return True
                gevent.sleep(1)
            else:
                return True

def _lock(fileno):
    """Try to lock a file. Return True on success."""
    # closing the file unlocks it, so we don't need to unlock here
    if platform.system() == 'Windows':
        try:
            msvcrt.locking(fileno, msvcrt.LK_NBLCK, 10)
            return True
        except PermissionError:
            return False
    else:
        try:
            fcntl.lockf(fileno, fcntl.LOCK_EX | fcntl.LOCK_NB)
            return True
        # the docs recommend catching both of these
        except (BlockingIOError, PermissionError):
            return False

def config_cache_lock():
    """
    Obtain the config cache lock, perform the code
    in the context and then let the lock go.
    :yield None
    :return None:
    """
    with open(conf().CONFIG_CACHE_LOCK, 'w+') as lock:
        try:
            log.debug(
                "Getting config cache lock. "
                "If this blocks forever, try deleting file "
                "{} and restart the process.".format(conf().CONFIG_CACHE_LOCK)
            )
            flock(lock, LOCK_EX)  # Blocks until lock becomes available
            yield
        finally:
            log.debug("Releasing the config cache lock")
            flock(lock, LOCK_UN)

def is_tor_data_dir_usable(tor_data_dir):
    """
    Checks if the Tor data dir specified is usable. This means that
     it is not being locked and we have permissions to write to it.
    """
    if not os.path.exists(tor_data_dir):
        return True

    try:
        fcntl.flock(open(os.path.join(tor_data_dir, 'lock'), 'w'),
                    fcntl.LOCK_EX | fcntl.LOCK_NB)
        return True
    except (IOError, OSError) as err:
        if err.errno == errno.EACCES:
            # Permission error
            return False
        elif err.errno == errno.EAGAIN:
            # File locked
            return False

def update(path):
    """
    allow concurrent update of metadata
    """
    p = os.path.join(path, "metadata.json")
    # we have to open writeable to get a lock
    with open(p, "a") as f:
        fcntl.lockf(f, fcntl.LOCK_EX)
        data = load(path)
        yield(data)
        save(path, data)
        fcntl.lockf(f, fcntl.LOCK_UN)

def main():
    exit_status = 1
    try:
        args = parse_args()
        # Make sure the exporter is only running once.
        lock_file = '/var/lock/{}.lock'.format(os.path.basename(sys.argv[0]))
        lock_fd = os.open(lock_file, os.O_CREAT)
        lock_success = False
        try:
            fcntl.flock(lock_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
            lock_success = True
        except IOError:
            msg = 'Failed to export metrics, another instance is running.'
            syslog.syslog(syslog.LOG_INFO, msg)
            sys.stderr.write(msg + '\n')
        if lock_success:
            # Create a new registry, otherwise unwanted default collectors are
            # added automatically.
            registry = prometheus_client.CollectorRegistry()
            # Register our own collector and write metrics to STDOUT.
            registry.register(CephRgwCollector(**vars(args)))
            sys.stdout.write(prometheus_client.generate_latest(registry))
            sys.stdout.flush()
            # Unlock the lock file.
            fcntl.flock(lock_fd, fcntl.LOCK_UN)
            exit_status = 0
    except Exception as e:
        syslog.syslog(syslog.LOG_ERR, str(e))
    # Cleanup
    os.close(lock_fd)
    if lock_success:
        try:
            os.unlink(lock_file)
        except:
            pass
    sys.exit(exit_status)

def _lockonly(file):
    _msg('got file #', file.fileno())
    try:
        flock(file, LOCK_EX | LOCK_NB)
    except IOError:
        _msg('failed to lock')
        return False
    else:
        _msg('locked successfully')
        return True

def lock (self):
        '''
        Creates and holds on to the lock file with exclusive access.
        Returns True if lock successful, False if it is not, and raises
        an exception upon operating system errors encountered creating the
        lock file.
        '''
        try:
            #
            # Create or else open and trucate lock file, in read-write mode.
            #
            # A crashed app might not delete the lock file, so the
            # os.O_CREAT | os.O_EXCL combination that guarantees
            # atomic create isn't useful here.  That is, we don't want to
            # fail locking just because the file exists.
            #
            # Could use os.O_EXLOCK, but that doesn't exist yet in my Python
            #
            self.lockfd = os.open (self.lockfile,
                                   os.O_TRUNC | os.O_CREAT | os.O_RDWR)

            # Acquire exclusive lock on the file, but don't block waiting for it
            fcntl.flock (self.lockfd, fcntl.LOCK_EX | fcntl.LOCK_NB)

            # Writing to file is pointless, nobody can see it
            os.write (self.lockfd, "My Lockfile")

            return True
        except (OSError, IOError), e:
            # Lock cannot be acquired is okay, everything else reraise exception
            if e.errno in (errno.EACCES, errno.EAGAIN):
                return False
            else:
                raise

def __enter__(self):
        self.pidfile = open(self.path, "a+")
        try:
            fcntl.flock(self.pidfile.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
        except IOError:
            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 __init__(self, mutex_name):
            check_valid_mutex_name(mutex_name)
            filename = os.path.join(tempfile.gettempdir(), mutex_name)
            try:
                handle = open(filename, 'w')
                fcntl.flock(handle, fcntl.LOCK_EX | fcntl.LOCK_NB)
            except:
                self._release_mutex = NULL
                self._acquired = False
                try:
                    handle.close()
                except:
                    pass
            else:
                def release_mutex(*args, **kwargs):
                    # Note: can't use self here!
                    if not getattr(release_mutex, 'called', False):
                        release_mutex.called = True
                        try:
                            fcntl.flock(handle, fcntl.LOCK_UN)
                        except:
                            traceback.print_exc()
                        try:
                            handle.close()
                        except:
                            traceback.print_exc()
                        try:
                            # Removing is pretty much optional (but let's do it to keep the
                            # filesystem cleaner).
                            os.unlink(filename)
                        except:
                            pass

                # Don't use __del__: this approach doesn't have as many pitfalls.
                self._ref = weakref.ref(self, release_mutex)

                self._release_mutex = release_mutex
                self._acquired = True

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 trylock_or_exit(self, timeout=10):

        interval = 0.1
        n = int(timeout / interval) + 1
        flag = fcntl.LOCK_EX | fcntl.LOCK_NB

        for ii in range(n):

            fd = os.open(self.lockfile, os.O_RDWR | os.O_CREAT)

            fcntl.fcntl(fd, fcntl.F_SETFD,
                        fcntl.fcntl(fd, fcntl.F_GETFD, 0)
                        | fcntl.FD_CLOEXEC)

            try:
                fcntl.lockf(fd, flag)

                self.lockfp = os.fdopen(fd, 'w+r')
                break

            except IOError as e:
                os.close(fd)
                if e[0] == errno.EAGAIN:
                    time.sleep(interval)
                else:
                    raise

        else:
            logger.info("Failure acquiring lock %s" % (self.lockfile, ))
            sys.exit(1)

        logger.info("OK acquired lock %s" % (self.lockfile))

def lock_file_nonblocking(fileobj):
    # Use fcntl.flock instead of fcntl.lockf. lockf on pypy 1.7 seems
    # to ignore existing locks.

    try:
        fcntl.flock(fileobj, fcntl.LOCK_EX | fcntl.LOCK_NB)
    except IOError, ioe:
        if ioe.errno not in (errno.EACCES, errno.EAGAIN):
            raise
        return False
    return True

def lockfile(filename):
    with open(filename, "wb") as opened:
        fd = opened.fileno()
        try:
            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except IOError as ioe:
            if ioe.errno not in (errno.EACCES, errno.EAGAIN):
                raise
            yield False
        else:
            try:
                yield True
            finally:
                fcntl.flock(fd, fcntl.LOCK_UN)

def acquire(self):
        try:
            self._lock = open(self.lock_file, "w")
            flock(self._lock, LOCK_EX | LOCK_NB)
            logging.debug("Acquired exclusive lock on file: %s" % self.lock_file)
            return self._lock
        except Exception:
            logging.debug("Error acquiring lock on file: %s" % self.lock_file)
            if self._lock:
                self._lock.close()
            raise OperationError("Could not acquire lock on file: %s!" % self.lock_file)

def trylock(self):
        fcntl.lockf(self.lockfile, fcntl.LOCK_EX | fcntl.LOCK_NB)

def __init__(self):
        self.fh = None
        self.is_running = False
        try:
            self.fh = open(LOCK_PATH, 'w')
            fcntl.lockf(self.fh, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except EnvironmentError as err:
            if self.fh is not None:
                self.is_running = True
            else:
                raise

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 _lock_file(f, exclusive):
        fcntl.flock(f, fcntl.LOCK_EX if exclusive else fcntl.LOCK_SH)

def latent_plan(init,goal,mode):
    bits = np.concatenate((init,goal))
    ###### preprocessing ################################################################

    ## old code for caching...
    lock = problem(network("lock"))
    import fcntl
    try:
        with open(lock) as f:
            print("lockfile found!")
            fcntl.flock(f, fcntl.LOCK_SH)
    except FileNotFoundError:
        with open(lock,'wb') as f:
            fcntl.flock(f, fcntl.LOCK_EX)
            preprocess(bits)

    ###### do planning #############################################
    sasp     = problem(network("{}.sasp".format(action_type)))
    plan_raw = problem(network("{}.sasp.plan".format(action_type)))
    plan     = problem(network("{}.{}.plan".format(action_type,mode)))

    echodo(["planner-scripts/limit.sh","-v", "-o",options[mode], "--","fd-sas-clean", sasp])
    assert os.path.exists(plan_raw)
    echodo(["mv",plan_raw,plan])

    out = echo_out(["lisp/parse-plan.bin",plan, *list(init.astype('str'))])
    lines = out.splitlines()
    return np.array([ [ int(s) for s in l.split() ] for l in lines ])

def openLocked(path, mode="w"):
    if os.name == "posix":
        import fcntl
        f = open(path, mode)
        fcntl.flock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
    else:
        f = open(path, mode)
    return f

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 __init__(self, fd, keys, excl=True, lock=False, mod=1048573, _ctx_cleanup=None):
        self.fd = fd
        self.locked = False
        self.mode = fcntl.LOCK_EX if excl else fcntl.LOCK_SH
        self._ctx_cleanup = _ctx_cleanup

        # sort so locks are acquired in consistent order
        # guarantees no inter-process deadlocks
        locks = set(hash(key) % mod for key in keys)
        self.locks = tuple(sorted(locks))

        if lock:
            self.lock()

def exclusive(self, *keys):
        self._update(fcntl.LOCK_EX)

def write_pid_file(pid_file, pid):
    try:
        fd = os.open(pid_file, os.O_RDWR | os.O_CREAT,
                     stat.S_IRUSR | stat.S_IWUSR)
    except OSError as e:
        LOG.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' % utils.to_str(r))
        else:
            logging.error('already started')
        os.close(fd)
        return -1
    os.ftruncate(fd, 0)
    os.write(fd, utils.to_bytes(str(pid)))
    return 0

def create_pid_file(self):

        fd = open(self._pid_file, 'wb')

        fcntl.lockf(fd, fcntl.LOCK_EX)

        timestamp = time.strftime('%Y-%m-%d %H:%M:%S')

        fd.write(self._pid + ";" + timestamp)
        fd.close()

        return True

def _trylock(lockfile):
        fcntl.lockf(lockfile, fcntl.LOCK_EX | fcntl.LOCK_NB)

def __init__(self, filename, mode='rb'):
        self.filename = filename
        self.mode = mode
        self.file = None
        if 'r' in mode:
            self.file = open_file(filename, mode)
            lock(self.file, LOCK_SH)
        elif 'w' in mode or 'a' in mode:
            self.file = open_file(filename, mode.replace('w', 'a'))
            lock(self.file, LOCK_EX)
            if 'a' not in mode:
                self.file.seek(0)
                self.file.truncate(0)
        else:
            raise RuntimeError("invalid LockedFile(...,mode)")

def acquire(self):
            fcntl.flock(self.handle, fcntl.LOCK_EX)

def _try_lock(self, fd):
        """Try to acquire the lock file without blocking.

        :param int fd: file descriptor of the opened file to lock

        """
        try:
            fcntl.lockf(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except IOError as err:
            if err.errno in (errno.EACCES, errno.EAGAIN):
                logger.debug(
                    "A lock on %s is held by another process.", self._path)
                raise errors.LockError(
                    "Another instance of Certbot is already running.")
            raise

def run(self):
        """
        THIS IS BLOCKING! CALL IT AT LAST!
        """
        with open(Job.lockFileName, 'w') as f:
            rv = fcntl.lockf(f.fileno(), fcntl.LOCK_EX)
            print("job {} is running.".format(os.getpid()))
            f.write(str(os.getpid()) + '\n')
            f.flush()
            self.action()
            fcntl.lockf(f.fileno(), fcntl.LOCK_UN)

def write_server_info(filename, port):
    pid = os.getpid()
    rank = MPI.COMM_WORLD.Get_rank()
    server_info = '{}:{}:{}:{}:{}'.format(LINE_TOKEN, rank, pid, port, LINE_TOKEN).strip()
    logger.debug("write_server_info: line %s, filename %s", server_info, filename)

    time.sleep(0.1 * rank)
    with open(filename, "a") as f:
        fcntl.lockf(f, fcntl.LOCK_EX)
        f.write(server_info + '\n')
        f.flush()
        os.fsync(f.fileno())
        fcntl.lockf(f, fcntl.LOCK_UN)
    return server_info

def _lock_file(f, exclusive):
            fcntl.flock(f, fcntl.LOCK_EX if exclusive else fcntl.LOCK_SH)