Source code for kazoo.recipe.watchers

"""Higher level child and data watching API's.

:Maintainer: Ben Bangert <ben@groovie.org>
:Status: Production

.. note::

    :ref:`DataWatch` and :ref:`ChildrenWatch` may only handle a single
    function, attempts to associate a single instance with multiple functions
    will result in an exception being thrown.

"""
from functools import partial, wraps
import logging
import time
import warnings

from kazoo.exceptions import (
    ConnectionClosedError,
    NoNodeError,
    KazooException
)
from kazoo.protocol.states import KazooState
from kazoo.retry import KazooRetry


log = logging.getLogger(__name__)


_STOP_WATCHING = object()


def _ignore_closed(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        try:
            return func(*args, **kwargs)
        except ConnectionClosedError:
            pass
    return wrapper


[docs]class DataWatch(object): """Watches a node for data updates and calls the specified function each time it changes The function will also be called the very first time its registered to get the data. Returning `False` from the registered function will disable future data change calls. If the client connection is closed (using the close command), the DataWatch will no longer get updates. If the function supplied takes three arguments, then the third one will be a :class:`~kazoo.protocol.states.WatchedEvent`. It will only be set if the change to the data occurs as a result of the server notifying the watch that there has been a change. Events like reconnection or the first call will not include an event. If the node does not exist, then the function will be called with ``None`` for all values. .. tip:: Because :class:`DataWatch` can watch nodes that don't exist, it can be used alternatively as a higher-level Exists watcher that survives reconnections and session loss. Example with client: .. code-block:: python @client.DataWatch('/path/to/watch') def my_func(data, stat): print("Data is %s" % data) print("Version is %s" % stat.version) # Above function is called immediately and prints # Or if you want the event object @client.DataWatch('/path/to/watch') def my_func(data, stat, event): print("Data is %s" % data) print("Version is %s" % stat.version) print("Event is %s" % event) .. versionchanged:: 1.2 DataWatch now ignores additional arguments that were previously passed to it and warns that they are no longer respected. """
[docs] def __init__(self, client, path, func=None, *args, **kwargs): """Create a data watcher for a path :param client: A zookeeper client. :type client: :class:`~kazoo.client.KazooClient` :param path: The path to watch for data changes on. :type path: str :param func: Function to call initially and every time the node changes. `func` will be called with a tuple, the value of the node and a :class:`~kazoo.client.ZnodeStat` instance. :type func: callable """ self._client = client self._path = path self._func = func self._stopped = False self._run_lock = client.handler.lock_object() self._version = None self._retry = KazooRetry(max_tries=None, sleep_func=client.handler.sleep_func) self._include_event = None self._ever_called = False self._used = False if args or kwargs: warnings.warn('Passing additional arguments to DataWatch is' ' deprecated. ignore_missing_node is now assumed ' ' to be True by default, and the event will be ' ' sent if the function can handle receiving it', DeprecationWarning, stacklevel=2) # Register our session listener if we're going to resume # across session losses if func is not None: self._used = True self._client.add_listener(self._session_watcher) self._get_data()
[docs] def __call__(self, func): """Callable version for use as a decorator :param func: Function to call initially and every time the data changes. `func` will be called with a tuple, the value of the node and a :class:`~kazoo.client.ZnodeStat` instance. :type func: callable """ if self._used: raise KazooException( "A function has already been associated with this " "DataWatch instance.") self._func = func self._used = True self._client.add_listener(self._session_watcher) self._get_data() return func
def _log_func_exception(self, data, stat, event=None): try: # For backwards compatibility, don't send event to the # callback unless the send_event is set in constructor if not self._ever_called: self._ever_called = True try: result = self._func(data, stat, event) except TypeError: result = self._func(data, stat) if result is False: self._stopped = True self._func = None self._client.remove_listener(self._session_watcher) except Exception as exc: log.exception(exc) raise @_ignore_closed def _get_data(self, event=None): # Ensure this runs one at a time, possible because the session # watcher may trigger a run with self._run_lock: if self._stopped: return initial_version = self._version try: data, stat = self._retry(self._client.get, self._path, self._watcher) except NoNodeError: data = None # This will set 'stat' to None if the node does not yet # exist. stat = self._retry(self._client.exists, self._path, self._watcher) if stat: self._client.handler.spawn(self._get_data) return # No node data, clear out version if stat is None: self._version = None else: self._version = stat.mzxid # Call our function if its the first time ever, or if the # version has changed if initial_version != self._version or not self._ever_called: self._log_func_exception(data, stat, event) def _watcher(self, event): self._get_data(event=event) def _set_watch(self, state): with self._run_lock: self._watch_established = state def _session_watcher(self, state): if state == KazooState.CONNECTED: self._client.handler.spawn(self._get_data)
[docs]class ChildrenWatch(object): """Watches a node for children updates and calls the specified function each time it changes The function will also be called the very first time its registered to get children. Returning `False` from the registered function will disable future children change calls. If the client connection is closed (using the close command), the ChildrenWatch will no longer get updates. if send_event=True in __init__, then the function will always be called with second parameter, ``event``. Upon initial call or when recovering a lost session the ``event`` is always ``None``. Otherwise it's a :class:`~kazoo.prototype.state.WatchedEvent` instance. Example with client: .. code-block:: python @client.ChildrenWatch('/path/to/watch') def my_func(children): print "Children are %s" % children # Above function is called immediately and prints children """
[docs] def __init__(self, client, path, func=None, allow_session_lost=True, send_event=False): """Create a children watcher for a path :param client: A zookeeper client. :type client: :class:`~kazoo.client.KazooClient` :param path: The path to watch for children on. :type path: str :param func: Function to call initially and every time the children change. `func` will be called with a single argument, the list of children. :type func: callable :param allow_session_lost: Whether the watch should be re-registered if the zookeeper session is lost. :type allow_session_lost: bool :type send_event: bool :param send_event: Whether the function should be passed the event sent by ZooKeeper or None upon initialization (see class documentation) The path must already exist for the children watcher to run. """ self._client = client self._path = path self._func = func self._send_event = send_event self._stopped = False self._watch_established = False self._allow_session_lost = allow_session_lost self._run_lock = client.handler.lock_object() self._prior_children = None self._used = False # Register our session listener if we're going to resume # across session losses if func is not None: self._used = True if allow_session_lost: self._client.add_listener(self._session_watcher) self._get_children()
[docs] def __call__(self, func): """Callable version for use as a decorator :param func: Function to call initially and every time the children change. `func` will be called with a single argument, the list of children. :type func: callable """ if self._used: raise KazooException( "A function has already been associated with this " "ChildrenWatch instance.") self._func = func self._used = True if self._allow_session_lost: self._client.add_listener(self._session_watcher) self._get_children() return func
@_ignore_closed def _get_children(self, event=None): with self._run_lock: # Ensure this runs one at a time if self._stopped: return try: children = self._client.retry(self._client.get_children, self._path, self._watcher) except NoNodeError: self._stopped = True return if not self._watch_established: self._watch_established = True if self._prior_children is not None and \ self._prior_children == children: return self._prior_children = children try: if self._send_event: result = self._func(children, event) else: result = self._func(children) if result is False: self._stopped = True self._func = None if self._allow_session_lost: self._client.remove_listener(self._session_watcher) except Exception as exc: log.exception(exc) raise def _watcher(self, event): if event.type != "NONE": self._get_children(event) def _session_watcher(self, state): if state in (KazooState.LOST, KazooState.SUSPENDED): self._watch_established = False elif (state == KazooState.CONNECTED and not self._watch_established and not self._stopped): self._client.handler.spawn(self._get_children)
[docs]class PatientChildrenWatch(object): """Patient Children Watch that returns values after the children of a node don't change for a period of time A separate watcher for the children of a node, that ignores changes within a boundary time and sets the result only when the boundary time has elapsed with no children changes. Example:: watcher = PatientChildrenWatch(client, '/some/path', time_boundary=5) async_object = watcher.start() # Blocks until the children have not changed for time boundary # (5 in this case) seconds, returns children list and an # async_result that will be set if the children change in the # future children, child_async = async_object.get() .. note:: This Watch is different from :class:`DataWatch` and :class:`ChildrenWatch` as it only returns once, does not take a function that is called, and provides an :class:`~kazoo.interfaces.IAsyncResult` object that can be checked to see if the children have changed later. """
[docs] def __init__(self, client, path, time_boundary=30): self.client = client self.path = path self.children = [] self.time_boundary = time_boundary self.children_changed = client.handler.event_object()
[docs] def start(self): """Begin the watching process asynchronously :returns: An :class:`~kazoo.interfaces.IAsyncResult` instance that will be set when no change has occurred to the children for time boundary seconds. """ self.asy = asy = self.client.handler.async_result() self.client.handler.spawn(self._inner_start) return asy
def _inner_start(self): try: while True: async_result = self.client.handler.async_result() self.children = self.client.retry( self.client.get_children, self.path, partial(self._children_watcher, async_result)) self.client.handler.sleep_func(self.time_boundary) if self.children_changed.is_set(): self.children_changed.clear() else: break self.asy.set((self.children, async_result)) except Exception as exc: self.asy.set_exception(exc) def _children_watcher(self, async_result, event): self.children_changed.set() async_result.set(time.time())