target.py

# -*- coding: utf-8 -*-
#
# Copyright 2012-2015 Spotify AB
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
"""
The abstract :py:class:`Target` class.
It is a central concept of Luigi and represents the state of the workflow.
"""

import errno
import time
import abc
import io
import os
import random
import tempfile
import logging
from luigi import six

logger = logging.getLogger('luigi-interface')


class FileLockException(Exception):
    pass


@six.add_metaclass(abc.ABCMeta)
class Target(object):

    """
    A Target is a resource generated by a :py:class:`~luigi.task.Task`.

    For example, a Target might correspond to a file in HDFS or data in a database. The Target
    interface defines one method that must be overridden: :py:meth:`exists`, which signifies if the
    Target has been created or not.

    Typically, a :py:class:`~luigi.task.Task` will define one or more Targets as output, and the Task
    is considered complete if and only if each of its output Targets exist.
    """

    @abc.abstractmethod
    def exists(self):
        """
        Returns ``True`` if the :py:class:`Target` exists and ``False`` otherwise.
        """
        pass


class FileSystemException(Exception):

    """
    Base class for generic file system exceptions.
    """
    pass


class FileAlreadyExists(FileSystemException):

    """
    Raised when a file system operation can't be performed because
    a directory exists but is required to not exist.
    """
    pass


class MissingParentDirectory(FileSystemException):

    """
    Raised when a parent directory doesn't exist.
    (Imagine mkdir without -p)
    """
    pass


@six.add_metaclass(abc.ABCMeta)
class FileSystem(object):

    """
    FileSystem abstraction used in conjunction with :py:class:`FileSystemTarget`.

    Typically, a FileSystem is associated with instances of a :py:class:`FileSystemTarget`. The
    instances of the py:class:`FileSystemTarget` will delegate methods such as
    :py:meth:`FileSystemTarget.exists` and :py:meth:`FileSystemTarget.remove` to the FileSystem.

    Methods of FileSystem raise :py:class:`FileSystemException` if there is a problem completing the
    operation.
    """

    @abc.abstractmethod
    def exists(self, path):
        """
        Return ``True`` if file or directory at ``path`` exist, ``False`` otherwise

        :param str path: a path within the FileSystem to check for existence.
        """
        pass

    @abc.abstractmethod
    def remove(self, path, recursive=True, skip_trash=True):
        """ Remove file or directory at location ``path``

        :param str path: a path within the FileSystem to remove.
        :param bool recursive: if the path is a directory, recursively remove the directory and all
                               of its descendants. Defaults to ``True``.
        """
        pass

    def mkdir(self, path, parents=True, raise_if_exists=False):
        """
        Create directory at location ``path``

        Creates the directory at ``path`` and implicitly create parent
        directories if they do not already exist.

        :param str path: a path within the FileSystem to create as a directory.
        :param bool parents: Create parent directories when necessary. When
                             parents=False and the parent directory doesn't
                             exist, raise luigi.target.MissingParentDirectory
        :param bool raise_if_exists: raise luigi.target.FileAlreadyExists if
                                     the folder already exists.

        *Note*: This method is optional, not all FileSystem subclasses implements it.

        *Note*: parents and raise_if_exists were added in August 2014. Some
                implementations might not support these flags yet.
        """
        raise NotImplementedError("mkdir() not implemented on {0}".format(self.__class__.__name__))

    def isdir(self, path):
        """
        Return ``True`` if the location at ``path`` is a directory. If not, return ``False``.

        :param str path: a path within the FileSystem to check as a directory.

        *Note*: This method is optional, not all FileSystem subclasses implements it.
        """
        raise NotImplementedError(
            "isdir() not implemented on {0}".format(
                self.__class__.__name__))


class FileSystemTarget(Target):

    """
    Base class for FileSystem Targets like :class:`~luigi.file.LocalTarget` and :class:`~luigi.hdfs.HdfsTarget`.

    A FileSystemTarget has an associated :py:class:`FileSystem` to which certain operations can be
    delegated. By default, :py:meth:`exists` and :py:meth:`remove` are delegated to the
    :py:class:`FileSystem`, which is determined by the :py:meth:`fs` property.

    Methods of FileSystemTarget raise :py:class:`FileSystemException` if there is a problem
    completing the operation.
    """

    def __init__(self, path):
        """
        Initializes a FileSystemTarget instance.

        :param str path: the path associated with this FileSystemTarget.
        """
        self.path = path

    @abc.abstractproperty
    def fs(self):
        """
        The :py:class:`FileSystem` associated with this FileSystemTarget.
        """
        raise

    @abc.abstractmethod
    def open(self, mode):
        """
        Open the FileSystem target.

        This method returns a file-like object which can either be read from or written to depending
        on the specified mode.

        :param str mode: the mode `r` opens the FileSystemTarget in read-only mode, whereas `w` will
                         open the FileSystemTarget in write mode. Subclasses can implement
                         additional options.
        """
        pass

    def exists(self):
        """
        Returns ``True`` if the path for this FileSystemTarget exists; ``False`` otherwise.

        This method is implemented by using :py:meth:`fs`.
        """
        path = self.path
        if '*' in path or '?' in path or '[' in path or '{' in path:
            logger.warning("Using wildcards in path %s might lead to processing of an incomplete dataset; "
                           "override exists() to suppress the warning.", path)
        return self.fs.exists(path)

    def remove(self):
        """
        Remove the resource at the path specified by this FileSystemTarget.

        This method is implemented by using :py:meth:`fs`.
        """
        self.fs.remove(self.path)


class AtomicLocalFile(io.BufferedWriter):

    """Abstract class to create Target that create
    a tempoprary file in the local filesystem before
    moving it to there final destination

    This class is just for the writing part of the Target. See
    :class:`luigi.file.LocalTarget` for example
    """

    def __init__(self, path):
        self.__tmp_path = self.generate_tmp_path(path)
        self.path = path
        super(AtomicLocalFile, self).__init__(io.FileIO(self.__tmp_path, 'w'))

    def close(self):
        super(AtomicLocalFile, self).close()
        self.move_to_final_destination()

    def generate_tmp_path(self, path):
        return os.path.join(tempfile.gettempdir(), 'luigi-s3-tmp-%09d' % random.randrange(0, 1e10))

    def move_to_final_destination(self):
        raise NotImplementedError()

    def __del__(self):
        if os.path.exists(self.tmp_path):
            os.remove(self.tmp_path)

    @property
    def tmp_path(self):
        return self.__tmp_path

    def __exit__(self, exc_type, exc, traceback):
        " Close/commit the file if there are no exception "
        if exc_type:
            return
        return super(AtomicLocalFile, self).__exit__(exc_type, exc, traceback)


class AtomicLocalFileAppend(io.BufferedWriter):

    def __init__(self, path, timeout=10, delay=.05):
        self.path = path
        self.is_locked = False
        self.timeout = timeout
        self.delay = delay
        self.lockfile = "%s.lock" % self.path
        self.acquire()
        super(AtomicLocalFileAppend, self).__init__(io.FileIO(self.path, 'a+'))

    def __exit__(self, exc_type, exc, traceback):
        if exc_type:
            return
        self.release()
        return super(AtomicLocalFileAppend, self).__exit__(exc_type, exc, traceback)

    def acquire(self):
        start_time = time.time()
        while True:
            try:
                self.fd = os.open(
                    self.lockfile,
                    os.O_CREAT | os.O_EXCL | os.O_RDWR)
                break
            except OSError as e:
                if e.errno != errno.EEXIST:
                    raise
                if (time.time() - start_time) >= self.timeout:
                    raise FileLockException("Timeout occured.")
                time.sleep(self.delay)
        self.is_locked = True

    def release(self):
        if self.is_locked:
            os.close(self.fd)
            os.unlink(self.lockfile)
            self.is_locked = False