Source code for kazoo.handlers.gevent

"""A gevent based handler."""
from __future__ import absolute_import

import logging

import gevent
from gevent import socket
import gevent.event
import gevent.queue
import gevent.select
import gevent.thread
try:
    from gevent.lock import Semaphore, RLock
except ImportError:
    from gevent.coros import Semaphore, RLock

from kazoo.handlers import utils
from kazoo import python2atexit


_using_libevent = gevent.__version__.startswith('0.')

log = logging.getLogger(__name__)

_STOP = object()

AsyncResult = gevent.event.AsyncResult


[docs]class SequentialGeventHandler(object): """Gevent handler for sequentially executing callbacks. This handler executes callbacks in a sequential manner. A queue is created for each of the callback events, so that each type of event has its callback type run sequentially. Each queue type has a greenlet worker that pulls the callback event off the queue and runs it in the order the client sees it. This split helps ensure that watch callbacks won't block session re-establishment should the connection be lost during a Zookeeper client call. Watch callbacks should avoid blocking behavior as the next callback of that type won't be run until it completes. If you need to block, spawn a new greenlet and return immediately so callbacks can proceed. """ name = "sequential_gevent_handler" queue_impl = gevent.queue.Queue queue_empty = gevent.queue.Empty sleep_func = staticmethod(gevent.sleep) def __init__(self): """Create a :class:`SequentialGeventHandler` instance""" self.callback_queue = self.queue_impl() self._running = False self._async = None self._state_change = Semaphore() self._workers = [] class timeout_exception(gevent.Timeout): def __init__(self, msg): gevent.Timeout.__init__(self, exception=msg) def _create_greenlet_worker(self, queue): def greenlet_worker(): while True: try: func = queue.get() try: if func is _STOP: break func() except Exception as exc: log.warning("Exception in worker greenlet") log.exception(exc) finally: del func # release before possible idle except self.queue_empty: continue return gevent.spawn(greenlet_worker)
[docs] def start(self): """Start the greenlet workers.""" with self._state_change: if self._running: return self._running = True # Spawn our worker greenlets, we have # - A callback worker for watch events to be called for queue in (self.callback_queue,): w = self._create_greenlet_worker(queue) self._workers.append(w) python2atexit.register(self.stop)
[docs] def stop(self): """Stop the greenlet workers and empty all queues.""" with self._state_change: if not self._running: return self._running = False for queue in (self.callback_queue,): queue.put(_STOP) while self._workers: worker = self._workers.pop() worker.join() # Clear the queues self.callback_queue = self.queue_impl() # pragma: nocover python2atexit.unregister(self.stop)
def select(self, *args, **kwargs): return gevent.select.select(*args, **kwargs) def socket(self, *args, **kwargs): return utils.create_tcp_socket(socket) def create_connection(self, *args, **kwargs): return utils.create_tcp_connection(socket, *args, **kwargs) def create_socket_pair(self): return utils.create_socket_pair(socket)
[docs] def event_object(self): """Create an appropriate Event object""" return gevent.event.Event()
[docs] def lock_object(self): """Create an appropriate Lock object""" return gevent.thread.allocate_lock()
[docs] def rlock_object(self): """Create an appropriate RLock object""" return RLock()
[docs] def async_result(self): """Create a :class:`AsyncResult` instance The :class:`AsyncResult` instance will have its completion callbacks executed in the thread the :class:`SequentialGeventHandler` is created in (which should be the gevent/main thread). """ return AsyncResult()
[docs] def spawn(self, func, *args, **kwargs): """Spawn a function to run asynchronously""" return gevent.spawn(func, *args, **kwargs)
[docs] def dispatch_callback(self, callback): """Dispatch to the callback object The callback is put on separate queues to run depending on the type as documented for the :class:`SequentialGeventHandler`. """ self.callback_queue.put(lambda: callback.func(*callback.args))