Source code for kazoo.handlers.threading

"""A threading based handler.

The :class:`SequentialThreadingHandler` is intended for regular Python
environments that use threads.

.. warning::

    Do not use :class:`SequentialThreadingHandler` with applications
    using asynchronous event loops (like gevent). Use the
    :class:`~kazoo.handlers.gevent.SequentialGeventHandler` instead.

from __future__ import absolute_import

import atexit
import logging
import select
import socket
import threading
import time

    import Queue
except ImportError:  # pragma: nocover
    import queue as Queue

from kazoo.handlers.utils import create_tcp_socket, create_tcp_connection

# sentinel objects
_NONE = object()
_STOP = object()

log = logging.getLogger(__name__)

[docs]class TimeoutError(Exception): pass
[docs]class AsyncResult(object): """A one-time event that stores a value or an exception""" def __init__(self, handler): self._handler = handler self.value = None self._exception = _NONE self._condition = threading.Condition() self._callbacks = []
[docs] def ready(self): """Return true if and only if it holds a value or an exception""" return self._exception is not _NONE
[docs] def successful(self): """Return true if and only if it is ready and holds a value""" return self._exception is None
@property def exception(self): if self._exception is not _NONE: return self._exception
[docs] def set(self, value=None): """Store the value. Wake up the waiters.""" with self._condition: self.value = value self._exception = None for callback in self._callbacks: self._handler.completion_queue.put( lambda: callback(self) ) self._condition.notify_all()
[docs] def set_exception(self, exception): """Store the exception. Wake up the waiters.""" with self._condition: self._exception = exception for callback in self._callbacks: self._handler.completion_queue.put( lambda: callback(self) ) self._condition.notify_all()
[docs] def get(self, block=True, timeout=None): """Return the stored value or raise the exception. If there is no value raises TimeoutError. """ with self._condition: if self._exception is not _NONE: if self._exception is None: return self.value raise self._exception elif block: self._condition.wait(timeout) if self._exception is not _NONE: if self._exception is None: return self.value raise self._exception # if we get to this point we timeout raise TimeoutError()
[docs] def get_nowait(self): """Return the value or raise the exception without blocking. If nothing is available, raises TimeoutError """ return self.get(block=False)
[docs] def wait(self, timeout=None): """Block until the instance is ready.""" with self._condition: self._condition.wait(timeout) return self._exception is not _NONE
[docs]class SequentialThreadingHandler(object): """Threading 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. These are split into two queues, one for watch events and one for async result completion callbacks. Each queue type has a thread 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 and completion 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 thread and return immediately so callbacks can proceed. .. note:: Completion callbacks can block to wait on Zookeeper calls, but no other completion callbacks will execute until the callback returns. """ name = "sequential_threading_handler" timeout_exception = TimeoutError sleep_func = staticmethod(time.sleep) queue_impl = Queue.Queue queue_empty = Queue.Empty def __init__(self): """Create a :class:`SequentialThreadingHandler` instance""" self.callback_queue = self.queue_impl() self.completion_queue = self.queue_impl() self._running = False self._state_change = threading.Lock() self._workers = [] def _create_thread_worker(self, queue): def thread_worker(): # pragma: nocover while True: try: func = queue.get() try: if func is _STOP: break func() except Exception: log.exception("Exception in worker queue thread") finally: queue.task_done() except self.queue_empty: continue t = threading.Thread(target=thread_worker) # Even though these should be joined, it's possible stop might # not issue in time so we set them to daemon to let the program # exit anyways t.daemon = True t.start() return t
[docs] def start(self): """Start the worker threads.""" with self._state_change: if self._running: return # Spawn our worker threads, we have # - A callback worker for watch events to be called # - A completion worker for completion events to be called for queue in (self.completion_queue, self.callback_queue): w = self._create_thread_worker(queue) self._workers.append(w) self._running = True atexit.register(self.stop)
[docs] def stop(self): """Stop the worker threads and empty all queues.""" with self._state_change: if not self._running: return self._running = False for queue in (self.completion_queue, self.callback_queue): queue.put(_STOP) self._workers.reverse() while self._workers: worker = self._workers.pop() worker.join() # Clear the queues self.callback_queue = self.queue_impl() self.completion_queue = self.queue_impl() if hasattr(atexit, "unregister"): atexit.unregister(self.stop)
def select(self, *args, **kwargs): return*args, **kwargs) def socket(self): return create_tcp_socket(socket) def create_connection(self, *args, **kwargs): return create_tcp_connection(socket, *args, **kwargs)
[docs] def event_object(self): """Create an appropriate Event object""" return threading.Event()
[docs] def lock_object(self): """Create a lock object""" return threading.Lock()
[docs] def rlock_object(self): """Create an appropriate RLock object""" return threading.RLock()
[docs] def async_result(self): """Create a :class:`AsyncResult` instance""" return AsyncResult(self)
def spawn(self, func, *args, **kwargs): t = threading.Thread(target=func, args=args, kwargs=kwargs) t.daemon = True t.start() return t
[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:`SequentialThreadingHandler`. """ self.callback_queue.put(lambda: callback.func(*callback.args))