540 lines
18 KiB
Python
540 lines
18 KiB
Python
"""
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Connection pooling and host management.
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"""
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import logging
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import time
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from threading import Lock, RLock, Condition
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import traceback
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import weakref
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try:
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from weakref import WeakSet
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except ImportError:
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from cassandra.util import WeakSet
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from cassandra import AuthenticationFailed
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from cassandra.connection import MAX_STREAM_PER_CONNECTION, ConnectionException
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log = logging.getLogger(__name__)
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class NoConnectionsAvailable(Exception):
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"""
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All existing connections to a given host are busy, or there are
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no open connections.
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"""
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pass
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class Host(object):
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"""
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Represents a single Cassandra node.
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"""
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address = None
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"""
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The IP address or hostname of the node.
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"""
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monitor = None
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"""
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A :class:`.HealthMonitor` instance that tracks whether this node is
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up or down.
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"""
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_datacenter = None
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_rack = None
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_reconnection_handler = None
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def __init__(self, inet_address, conviction_policy_factory):
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if inet_address is None:
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raise ValueError("inet_address may not be None")
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if conviction_policy_factory is None:
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raise ValueError("conviction_policy_factory may not be None")
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self.address = inet_address
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self.monitor = HealthMonitor(conviction_policy_factory(self))
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self._reconnection_lock = Lock()
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@property
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def datacenter(self):
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""" The datacenter the node is in. """
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return self._datacenter
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@property
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def rack(self):
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""" The rack the node is in. """
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return self._rack
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def set_location_info(self, datacenter, rack):
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"""
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Sets the datacenter and rack for this node. Intended for internal
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use (by the control connection, which periodically checks the
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ring topology) only.
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"""
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self._datacenter = datacenter
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self._rack = rack
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def get_and_set_reconnection_handler(self, new_handler):
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"""
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Atomically replaces the reconnection handler for this
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host. Intended for internal use only.
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"""
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with self._reconnection_lock:
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old = self._reconnection_handler
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self._reconnection_handler = new_handler
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return old
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def __eq__(self, other):
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if not isinstance(other, Host):
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return False
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return self.address == other.address
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def __str__(self):
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return self.address
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def __repr__(self):
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dc = (" %s" % (self._datacenter,)) if self._datacenter else ""
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return "<%s: %s%s>" % (self.__class__.__name__, self.address, dc)
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class _ReconnectionHandler(object):
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"""
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Abstract class for attempting reconnections with a given
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schedule and scheduler.
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"""
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_cancelled = False
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def __init__(self, scheduler, schedule, callback, *callback_args, **callback_kwargs):
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self.scheduler = scheduler
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self.schedule = schedule
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self.callback = callback
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self.callback_args = callback_args
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self.callback_kwargs = callback_kwargs
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def start(self):
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if self._cancelled:
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return
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# TODO cancel previous reconnection handlers? That's probably the job
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# of whatever created this.
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first_delay = self.schedule.next()
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self.scheduler.schedule(first_delay, self.run)
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def run(self):
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if self._cancelled:
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self.callback(*(self.callback_args), **(self.callback_kwargs))
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try:
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self.on_reconnection(self.try_reconnect())
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except Exception, exc:
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next_delay = self.schedule.next()
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if self.on_exception(exc, next_delay):
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self.scheduler.schedule(next_delay, self.run)
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else:
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self.callback(*(self.callback_args), **(self.callback_kwargs))
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def cancel(self):
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self._cancelled = True
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def try_reconnect(self):
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"""
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Subclasses must implement this method. It should attempt to
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open a new Connection and return it; if a failure occurs, an
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Exception should be raised.
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"""
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raise NotImplementedError()
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def on_reconnection(self, connection):
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"""
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Called when a new Connection is successfully opened. Nothing is
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done by default.
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"""
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pass
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def on_exception(self, exc, next_delay):
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"""
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Called when an Exception is raised when trying to connect.
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`exc` is the Exception that was raised and `next_delay` is the
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number of seconds (as a float) that the handler will wait before
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attempting to connect again.
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Subclasses should return :const:`False` if no more attempts to
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connection should be made, :const:`True` otherwise. The default
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behavior is to always retry unless the error is an
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:exc:`.AuthenticationFailed` instance.
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"""
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if isinstance(exc, AuthenticationFailed):
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return False
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else:
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return True
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class _HostReconnectionHandler(_ReconnectionHandler):
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def __init__(self, host, connection_factory, *args, **kwargs):
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_ReconnectionHandler.__init__(self, *args, **kwargs)
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self.host = host
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self.connection_factory = connection_factory
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def try_reconnect(self):
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return self.connection_factory()
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def on_reconnection(self, connection):
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self.host.monitor.reset()
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def on_exception(self, exc, next_delay):
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if isinstance(exc, AuthenticationFailed):
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return False
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else:
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log.warn("Error attempting to reconnect to %s: %s", self.host, exc)
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log.debug(traceback.format_exc(exc))
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return True
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class HealthMonitor(object):
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"""
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Monitors whether a particular host is marked as up or down.
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This class is primarily intended for internal use, although
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applications may find it useful to check whether a given node
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is up or down.
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"""
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is_up = True
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"""
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A boolean representing the current state of the node.
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"""
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def __init__(self, conviction_policy):
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self._conviction_policy = conviction_policy
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self._host = conviction_policy.host
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# self._listeners will hold, among other things, references to
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# Cluster objects. To allow those to be GC'ed (and shutdown) even
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# though we've implemented __del__, use weak references.
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self._listeners = WeakSet()
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self._lock = RLock()
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def register(self, listener):
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with self._lock:
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self._listeners.add(listener)
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def unregister(self, listener):
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with self._lock:
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self._listeners.remove(listener)
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def set_up(self):
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if self.is_up:
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return
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self._conviction_policy.reset()
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log.info("Host %s is considered up", self._host)
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with self._lock:
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listeners = self._listeners.copy()
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for listener in listeners:
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listener.on_up(self._host)
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self.is_up = True
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def set_down(self):
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if not self.is_up:
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return
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self.is_up = False
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log.info("Host %s is considered down", self._host)
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with self._lock:
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listeners = self._listeners.copy()
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for listener in listeners:
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listener.on_down(self._host)
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def reset(self):
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return self.set_up()
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def signal_connection_failure(self, connection_exc):
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is_down = self._conviction_policy.add_failure(connection_exc)
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if is_down:
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self.set_down()
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return is_down
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_MAX_SIMULTANEOUS_CREATION = 1
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class HostConnectionPool(object):
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host = None
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host_distance = None
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is_shutdown = False
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open_count = 0
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_scheduled_for_creation = 0
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def __init__(self, host, host_distance, session):
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self.host = host
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self.host_distance = host_distance
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self._session = weakref.proxy(session)
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self._lock = RLock()
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self._conn_available_condition = Condition()
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core_conns = session.cluster.get_core_connections_per_host(host_distance)
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self._connections = [session.cluster.connection_factory(host.address)
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for i in range(core_conns)]
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self._trash = set()
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self.open_count = core_conns
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def borrow_connection(self, timeout):
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if self.is_shutdown:
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raise ConnectionException(
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"Pool for %s is shutdown" % (self.host,), self.host)
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conns = self._connections
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if not conns:
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# handled specially just for simpler code
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log.debug("Detected empty pool, opening core conns to %s" % (self.host,))
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core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
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with self._lock:
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# we check the length of self._connections again
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# along with self._scheduled_for_creation while holding the lock
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# in case multiple threads hit this condition at the same time
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to_create = core_conns - (len(self._connections) + self._scheduled_for_creation)
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for i in range(to_create):
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self._scheduled_for_creation += 1
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self._session.submit(self._create_new_connection)
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# in_flight is incremented by wait_for_conn
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conn = self._wait_for_conn(timeout)
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conn.set_keyspace(self._session.keyspace)
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return conn
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else:
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# note: it would be nice to push changes to these config settings
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# to pools instead of doing a new lookup on every
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# borrow_connection() call
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max_reqs = self._session.cluster.get_max_requests_per_connection(self.host_distance)
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max_conns = self._session.cluster.get_max_connections_per_host(self.host_distance)
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least_busy = min(conns, key=lambda c: c.in_flight)
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# to avoid another thread closing this connection while
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# trashing it (through the return_connection process), hold
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# the connection lock from this point until we've incremented
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# its in_flight count
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with least_busy.lock:
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# if we have too many requests on this connection but we still
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# have space to open a new connection against this host, go ahead
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# and schedule the creation of a new connection
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if least_busy.in_flight >= max_reqs and len(self._connections) < max_conns:
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self._maybe_spawn_new_connection()
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if least_busy.in_flight >= MAX_STREAM_PER_CONNECTION:
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# once we release the lock, wait for another connection
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need_to_wait = True
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else:
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need_to_wait = False
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least_busy.in_flight += 1
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if need_to_wait:
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# wait_for_conn will increment in_flight on the conn
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least_busy = self._wait_for_conn(timeout)
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least_busy.set_keyspace(self._session.keyspace)
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return least_busy
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def _maybe_spawn_new_connection(self):
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with self._lock:
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if self._scheduled_for_creation >= _MAX_SIMULTANEOUS_CREATION:
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return
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self._scheduled_for_creation += 1
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log.debug("Submitting task for creation of new Connection to %s" % (self.host,))
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self._session.submit(self._create_new_connection)
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def _create_new_connection(self):
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try:
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self._add_conn_if_under_max()
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except Exception:
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log.exception("Unexpectedly failed to create new connection")
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finally:
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with self._lock:
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self._scheduled_for_creation -= 1
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def _add_conn_if_under_max(self):
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max_conns = self._session.cluster.get_max_connections_per_host(self.host_distance)
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with self._lock:
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if self.is_shutdown:
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return False
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if self.open_count >= max_conns:
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return False
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self.open_count += 1
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try:
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conn = self._session.cluster.connection_factory(self.host.address)
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with self._lock:
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new_connections = self._connections[:] + [conn]
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self._connections = new_connections
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self._signal_available_conn()
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return True
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except ConnectionException, exc:
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log.exception("Failed to add new connection to pool for host %s" % (self.host,))
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with self._lock:
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self.open_count -= 1
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if self.host.monitor.signal_connection_failure(exc):
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self.shutdown()
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return False
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except AuthenticationFailed:
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with self._lock:
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self.open_count -= 1
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return False
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def _await_available_conn(self, timeout):
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with self._conn_available_condition:
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self._conn_available_condition.wait(timeout)
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def _signal_available_conn(self):
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with self._conn_available_condition:
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self._conn_available_condition.notify()
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def _signal_all_available_conn(self):
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with self._conn_available_condition:
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self._conn_available_condition.notify_all()
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def _wait_for_conn(self, timeout):
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start = time.time()
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remaining = timeout
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while remaining > 0:
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# wait on our condition for the possibility that a connection
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# is useable
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self._await_available_conn(remaining)
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# self.shutdown() may trigger the above Condition
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if self.is_shutdown:
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raise ConnectionException("Pool is shutdown")
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conns = self._connections
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if conns:
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least_busy = min(conns, key=lambda c: c.in_flight)
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with least_busy.lock:
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if least_busy.in_flight < MAX_STREAM_PER_CONNECTION:
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least_busy.in_flight += 1
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return least_busy
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remaining = timeout - (time.time() - start)
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raise NoConnectionsAvailable()
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def return_connection(self, connection):
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with connection.lock:
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connection.in_flight -= 1
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in_flight = connection.in_flight
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if connection.is_defunct or connection.is_closed:
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is_down = self.host.monitor.signal_connection_failure(connection.last_error)
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if is_down:
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self.shutdown()
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else:
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self._replace(connection)
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else:
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if connection in self._trash:
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with connection.lock:
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if in_flight == 0:
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with self._lock:
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self._trash.remove(connection)
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connection.close()
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return
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core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
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min_reqs = self._session.cluster.get_min_requests_per_connection(self.host_distance)
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# we can use in_flight here without holding the connection lock
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# because the fact that in_flight dipped below the min at some
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# point is enough to start the trashing procedure
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if len(self._connections) > core_conns and in_flight <= min_reqs:
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self._maybe_trash_connection(connection)
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else:
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self._signal_available_conn()
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def _maybe_trash_connection(self, connection):
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core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
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did_trash = False
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with self._lock:
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if connection not in self._connections:
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return
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if self.open_count > core_conns:
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did_trash = True
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self.open_count -= 1
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new_connections = self._connections[:]
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new_connections.remove(connection)
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self._connections = new_connections
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with connection.lock:
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if connection.in_flight == 0:
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connection.close()
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# skip adding it to the trash if we're already closing it
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return
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self._trash.add(connection)
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if did_trash:
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log.debug("Trashed connection to %s" % (self.host,))
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def _replace(self, connection):
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should_replace = False
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with self._lock:
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if connection in self._connections:
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new_connections = self._connections[:]
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new_connections.remove(connection)
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self._connections = new_connections
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self.open_count -= 1
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should_replace = True
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if should_replace:
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log.debug("Replacing connection to %s" % (self.host,))
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def close_and_replace():
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connection.close()
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self._add_conn_if_under_max()
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self._session.submit(close_and_replace)
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else:
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# just close it
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log.debug("Closing connection to %s" % (self.host,))
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connection.close()
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def shutdown(self):
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with self._lock:
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if self.is_shutdown:
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return
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else:
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self.is_shutdown = True
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self._signal_all_available_conn()
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for conn in self._connections:
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conn.close()
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self.open_count -= 1
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reconnector = self.host.get_and_set_reconnection_handler(None)
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if reconnector:
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reconnector.cancel()
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def ensure_core_connections(self):
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if self.is_shutdown:
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return
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core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
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with self._lock:
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to_create = core_conns - (len(self._connections) + self._scheduled_for_creation)
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for i in range(to_create):
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self._scheduled_for_creation += 1
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self._session.submit(self._create_new_connection)
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