"""A gevent based handler."""
from __future__ import absolute_import
import logging
import gevent
import gevent.event
import gevent.queue
import gevent.select
import gevent.thread
from gevent.queue import Empty
from gevent.queue import Queue
from gevent import socket
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"
sleep_func = staticmethod(gevent.sleep)
def __init__(self):
"""Create a :class:`SequentialGeventHandler` instance"""
self.callback_queue = Queue()
self._running = False
self._async = None
self._state_change = Semaphore()
self._workers = []
class timeout_exception(gevent.event.Timeout):
def __init__(self, msg):
gevent.event.Timeout.__init__(self, exception=msg)
def _create_greenlet_worker(self, queue):
def greenlet_worker():
while True:
try:
func = queue.get()
if func is _STOP:
break
func()
except Empty:
continue
except Exception as exc:
log.warning("Exception in worker greenlet")
log.exception(exc)
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 = Queue() # 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))