FileMonitor/watchdog/observers/polling.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2011 Yesudeep Mangalapilly <yesudeep@gmail.com>
# Copyright 2012 Google, Inc.
#
# 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.


"""
:module: watchdog.observers.polling
:synopsis: Polling emitter implementation.
:author: yesudeep@google.com (Yesudeep Mangalapilly)

Classes
-------
.. autoclass:: PollingObserver
   :members:
   :show-inheritance:

.. autoclass:: PollingObserverVFS
   :members:
   :show-inheritance:
   :special-members:
"""

from __future__ import with_statement
import threading
from functools import partial
from watchdog.utils import stat as default_stat
from watchdog.utils.dirsnapshot import DirectorySnapshot, DirectorySnapshotDiff
from watchdog.observers.api import (
    EventEmitter,
    BaseObserver,
    DEFAULT_OBSERVER_TIMEOUT,
    DEFAULT_EMITTER_TIMEOUT
)

from watchdog.events import (
    DirMovedEvent,
    DirDeletedEvent,
    DirCreatedEvent,
    DirModifiedEvent,
    FileMovedEvent,
    FileDeletedEvent,
    FileCreatedEvent,
    FileModifiedEvent
)

try:
    from os import scandir
except ImportError:
    from os import listdir as scandir


class PollingEmitter(EventEmitter):
    """
    Platform-independent emitter that polls a directory to detect file
    system changes.
    """

    def __init__(self, event_queue, watch, timeout=DEFAULT_EMITTER_TIMEOUT,
                 stat=default_stat, listdir=scandir):
        EventEmitter.__init__(self, event_queue, watch, timeout)
        self._snapshot = None
        self._lock = threading.Lock()
        self._take_snapshot = lambda: DirectorySnapshot(
            self.watch.path, self.watch.is_recursive, stat=stat, listdir=listdir)

    def on_thread_start(self):
        self._snapshot = self._take_snapshot()

    def queue_events(self, timeout):
        # We don't want to hit the disk continuously.
        # timeout behaves like an interval for polling emitters.
        if self.stopped_event.wait(timeout):
            return

        with self._lock:
            if not self.should_keep_running():
                return

            # Get event diff between fresh snapshot and previous snapshot.
            # Update snapshot.
            try:
                new_snapshot = self._take_snapshot()
            except OSError:
                self.queue_event(DirDeletedEvent(self.watch.path))
                self.stop()
                return

            events = DirectorySnapshotDiff(self._snapshot, new_snapshot)
            self._snapshot = new_snapshot

            # Files.
            for src_path in events.files_deleted:
                self.queue_event(FileDeletedEvent(src_path))
            for src_path in events.files_modified:
                self.queue_event(FileModifiedEvent(src_path))
            for src_path in events.files_created:
                self.queue_event(FileCreatedEvent(src_path))
            for src_path, dest_path in events.files_moved:
                self.queue_event(FileMovedEvent(src_path, dest_path))

            # Directories.
            for src_path in events.dirs_deleted:
                self.queue_event(DirDeletedEvent(src_path))
            for src_path in events.dirs_modified:
                self.queue_event(DirModifiedEvent(src_path))
            for src_path in events.dirs_created:
                self.queue_event(DirCreatedEvent(src_path))
            for src_path, dest_path in events.dirs_moved:
                self.queue_event(DirMovedEvent(src_path, dest_path))


class PollingObserver(BaseObserver):
    """
    Platform-independent observer that polls a directory to detect file
    system changes.
    """

    def __init__(self, timeout=DEFAULT_OBSERVER_TIMEOUT):
        BaseObserver.__init__(self, emitter_class=PollingEmitter, timeout=timeout)


class PollingObserverVFS(BaseObserver):
    """
    File system independent observer that polls a directory to detect changes.
    """

    def __init__(self, stat, listdir, polling_interval=1):
        """
        :param stat: stat function. See ``os.stat`` for details.
        :param listdir: listdir function. See ``os.listdir`` for details.
        :type polling_interval: float
        :param polling_interval: interval in seconds between polling the file system.
        """
        emitter_cls = partial(PollingEmitter, stat=stat, listdir=listdir)
        BaseObserver.__init__(self, emitter_class=emitter_cls, timeout=polling_interval)