# Copyright 2013-2015 DataStax, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
Connection pooling and host management.
"""
import logging
import socket
import time
from threading import Lock, RLock, Condition
import weakref
try:
from weakref import WeakSet
except ImportError:
from cassandra.util import WeakSet # NOQA
from cassandra import AuthenticationFailed
from cassandra.connection import ConnectionException
from cassandra.policies import HostDistance
log = logging.getLogger(__name__)
[docs]class NoConnectionsAvailable(Exception):
"""
All existing connections to a given host are busy, or there are
no open connections.
"""
pass
[docs]class Host(object):
"""
Represents a single Cassandra node.
"""
address = None
"""
The IP address or hostname of the node.
"""
conviction_policy = None
"""
A :class:`~.ConvictionPolicy` instance for determining when this node should
be marked up or down.
"""
is_up = None
"""
:const:`True` if the node is considered up, :const:`False` if it is
considered down, and :const:`None` if it is not known if the node is
up or down.
"""
_datacenter = None
_rack = None
_reconnection_handler = None
lock = None
_currently_handling_node_up = False
def __init__(self, inet_address, conviction_policy_factory, datacenter=None, rack=None):
if inet_address is None:
raise ValueError("inet_address may not be None")
if conviction_policy_factory is None:
raise ValueError("conviction_policy_factory may not be None")
self.address = inet_address
self.conviction_policy = conviction_policy_factory(self)
self.set_location_info(datacenter, rack)
self.lock = RLock()
@property
def datacenter(self):
""" The datacenter the node is in. """
return self._datacenter
@property
def rack(self):
""" The rack the node is in. """
return self._rack
def set_location_info(self, datacenter, rack):
"""
Sets the datacenter and rack for this node. Intended for internal
use (by the control connection, which periodically checks the
ring topology) only.
"""
self._datacenter = datacenter
self._rack = rack
def set_up(self):
if not self.is_up:
log.debug("Host %s is now marked up", self.address)
self.conviction_policy.reset()
self.is_up = True
def set_down(self):
self.is_up = False
def signal_connection_failure(self, connection_exc):
return self.conviction_policy.add_failure(connection_exc)
def is_currently_reconnecting(self):
return self._reconnection_handler is not None
def get_and_set_reconnection_handler(self, new_handler):
"""
Atomically replaces the reconnection handler for this
host. Intended for internal use only.
"""
with self.lock:
old = self._reconnection_handler
self._reconnection_handler = new_handler
return old
def __eq__(self, other):
return self.address == other.address
def __hash__(self):
return hash(self.address)
def __lt__(self, other):
return self.address < other.address
def __str__(self):
return str(self.address)
def __repr__(self):
dc = (" %s" % (self._datacenter,)) if self._datacenter else ""
return "<%s: %s%s>" % (self.__class__.__name__, self.address, dc)
class _ReconnectionHandler(object):
"""
Abstract class for attempting reconnections with a given
schedule and scheduler.
"""
_cancelled = False
def __init__(self, scheduler, schedule, callback, *callback_args, **callback_kwargs):
self.scheduler = scheduler
self.schedule = schedule
self.callback = callback
self.callback_args = callback_args
self.callback_kwargs = callback_kwargs
def start(self):
if self._cancelled:
log.debug("Reconnection handler was cancelled before starting")
return
first_delay = next(self.schedule)
self.scheduler.schedule(first_delay, self.run)
def run(self):
if self._cancelled:
return
conn = None
try:
conn = self.try_reconnect()
except Exception as exc:
try:
next_delay = next(self.schedule)
except StopIteration:
# the schedule has been exhausted
next_delay = None
# call on_exception for logging purposes even if next_delay is None
if self.on_exception(exc, next_delay):
if next_delay is None:
log.warning(
"Will not continue to retry reconnection attempts "
"due to an exhausted retry schedule")
else:
self.scheduler.schedule(next_delay, self.run)
else:
if not self._cancelled:
self.on_reconnection(conn)
self.callback(*(self.callback_args), **(self.callback_kwargs))
finally:
if conn:
conn.close()
def cancel(self):
self._cancelled = True
def try_reconnect(self):
"""
Subclasses must implement this method. It should attempt to
open a new Connection and return it; if a failure occurs, an
Exception should be raised.
"""
raise NotImplementedError()
def on_reconnection(self, connection):
"""
Called when a new Connection is successfully opened. Nothing is
done by default.
"""
pass
def on_exception(self, exc, next_delay):
"""
Called when an Exception is raised when trying to connect.
`exc` is the Exception that was raised and `next_delay` is the
number of seconds (as a float) that the handler will wait before
attempting to connect again.
Subclasses should return :const:`False` if no more attempts to
connection should be made, :const:`True` otherwise. The default
behavior is to always retry unless the error is an
:exc:`.AuthenticationFailed` instance.
"""
if isinstance(exc, AuthenticationFailed):
return False
else:
return True
class _HostReconnectionHandler(_ReconnectionHandler):
def __init__(self, host, connection_factory, is_host_addition, on_add, on_up, *args, **kwargs):
_ReconnectionHandler.__init__(self, *args, **kwargs)
self.is_host_addition = is_host_addition
self.on_add = on_add
self.on_up = on_up
self.host = host
self.connection_factory = connection_factory
def try_reconnect(self):
return self.connection_factory()
def on_reconnection(self, connection):
log.info("Successful reconnection to %s, marking node up if it isn't already", self.host)
if self.is_host_addition:
self.on_add(self.host)
else:
self.on_up(self.host)
def on_exception(self, exc, next_delay):
if isinstance(exc, AuthenticationFailed):
return False
else:
log.warning("Error attempting to reconnect to %s, scheduling retry in %s seconds: %s",
self.host, next_delay, exc)
log.debug("Reconnection error details", exc_info=True)
return True
class HostConnection(object):
"""
When using v3 of the native protocol, this is used instead of a connection
pool per host (HostConnectionPool) due to the increased in-flight capacity
of individual connections.
"""
host = None
host_distance = None
is_shutdown = False
_session = None
_connection = None
_lock = None
def __init__(self, host, host_distance, session):
self.host = host
self.host_distance = host_distance
self._session = weakref.proxy(session)
self._lock = Lock()
if host_distance == HostDistance.IGNORED:
log.debug("Not opening connection to ignored host %s", self.host)
return
elif host_distance == HostDistance.REMOTE and not session.cluster.connect_to_remote_hosts:
log.debug("Not opening connection to remote host %s", self.host)
return
log.debug("Initializing connection for host %s", self.host)
self._connection = session.cluster.connection_factory(host.address)
if session.keyspace:
self._connection.set_keyspace_blocking(session.keyspace)
log.debug("Finished initializing connection for host %s", self.host)
def borrow_connection(self, timeout):
if self.is_shutdown:
raise ConnectionException(
"Pool for %s is shutdown" % (self.host,), self.host)
conn = self._connection
if not conn:
raise NoConnectionsAvailable()
with conn.lock:
if conn.in_flight < conn.max_request_id:
conn.in_flight += 1
return conn, conn.get_request_id()
raise NoConnectionsAvailable("All request IDs are currently in use")
def return_connection(self, connection):
with connection.lock:
connection.in_flight -= 1
if connection.is_defunct or connection.is_closed:
log.debug("Defunct or closed connection (%s) returned to pool, potentially "
"marking host %s as down", id(connection), self.host)
is_down = self._session.cluster.signal_connection_failure(
self.host, connection.last_error, is_host_addition=False)
if is_down:
self.shutdown()
else:
self._connection = None
with self._lock:
if self._is_replacing:
return
self._is_replacing = True
self._session.submit(self._replace, connection)
def _replace(self, connection):
log.debug("Replacing connection (%s) to %s", id(connection), self.host)
conn = self._session.cluster.connection_factory(self.host.address)
if self._session.keyspace:
conn.set_keyspace_blocking(self._session.keyspace)
self._connection = conn
with self._lock:
self._is_replacing = False
def shutdown(self):
with self._lock:
if self.is_shutdown:
return
else:
self.is_shutdown = True
if self._connection:
self._connection.close()
def _set_keyspace_for_all_conns(self, keyspace, callback):
if self.is_shutdown or not self._connection:
return
def connection_finished_setting_keyspace(conn, error):
self.return_connection(conn)
errors = [] if not error else [error]
callback(self, errors)
self._connection.set_keyspace_async(keyspace, connection_finished_setting_keyspace)
def get_connections(self):
c = self._connection
return [c] if c else []
def get_state(self):
connection = self._connection
open_count = 1 if connection and not (connection.is_closed or connection.is_defunct) else 0
in_flights = [connection.in_flight] if connection else []
return {'shutdown': self.is_shutdown, 'open_count': open_count, 'in_flights': in_flights}
@property
def open_count(self):
connection = self._connection
return 1 if connection and not (connection.is_closed or connection.is_defunct) else 0
_MAX_SIMULTANEOUS_CREATION = 1
_MIN_TRASH_INTERVAL = 10
class HostConnectionPool(object):
"""
Used to pool connections to a host for v1 and v2 native protocol.
"""
host = None
host_distance = None
is_shutdown = False
open_count = 0
_scheduled_for_creation = 0
_next_trash_allowed_at = 0
def __init__(self, host, host_distance, session):
self.host = host
self.host_distance = host_distance
self._session = weakref.proxy(session)
self._lock = RLock()
self._conn_available_condition = Condition()
log.debug("Initializing new connection pool for host %s", self.host)
core_conns = session.cluster.get_core_connections_per_host(host_distance)
self._connections = [session.cluster.connection_factory(host.address)
for i in range(core_conns)]
if session.keyspace:
for conn in self._connections:
conn.set_keyspace_blocking(session.keyspace)
self._trash = set()
self._next_trash_allowed_at = time.time()
self.open_count = core_conns
log.debug("Finished initializing new connection pool for host %s", self.host)
def borrow_connection(self, timeout):
if self.is_shutdown:
raise ConnectionException(
"Pool for %s is shutdown" % (self.host,), self.host)
conns = self._connections
if not conns:
# handled specially just for simpler code
log.debug("Detected empty pool, opening core conns to %s", self.host)
core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
with self._lock:
# we check the length of self._connections again
# along with self._scheduled_for_creation while holding the lock
# in case multiple threads hit this condition at the same time
to_create = core_conns - (len(self._connections) + self._scheduled_for_creation)
for i in range(to_create):
self._scheduled_for_creation += 1
self._session.submit(self._create_new_connection)
# in_flight is incremented by wait_for_conn
conn = self._wait_for_conn(timeout)
return conn
else:
# note: it would be nice to push changes to these config settings
# to pools instead of doing a new lookup on every
# borrow_connection() call
max_reqs = self._session.cluster.get_max_requests_per_connection(self.host_distance)
max_conns = self._session.cluster.get_max_connections_per_host(self.host_distance)
least_busy = min(conns, key=lambda c: c.in_flight)
request_id = None
# to avoid another thread closing this connection while
# trashing it (through the return_connection process), hold
# the connection lock from this point until we've incremented
# its in_flight count
need_to_wait = False
with least_busy.lock:
if least_busy.in_flight < least_busy.max_request_id:
least_busy.in_flight += 1
request_id = least_busy.get_request_id()
else:
# once we release the lock, wait for another connection
need_to_wait = True
if need_to_wait:
# wait_for_conn will increment in_flight on the conn
least_busy, request_id = self._wait_for_conn(timeout)
# if we have too many requests on this connection but we still
# have space to open a new connection against this host, go ahead
# and schedule the creation of a new connection
if least_busy.in_flight >= max_reqs and len(self._connections) < max_conns:
self._maybe_spawn_new_connection()
return least_busy, request_id
def _maybe_spawn_new_connection(self):
with self._lock:
if self._scheduled_for_creation >= _MAX_SIMULTANEOUS_CREATION:
return
if self.open_count >= self._session.cluster.get_max_connections_per_host(self.host_distance):
return
self._scheduled_for_creation += 1
log.debug("Submitting task for creation of new Connection to %s", self.host)
self._session.submit(self._create_new_connection)
def _create_new_connection(self):
try:
self._add_conn_if_under_max()
except (ConnectionException, socket.error) as exc:
log.warning("Failed to create new connection to %s: %s", self.host, exc)
except Exception:
log.exception("Unexpectedly failed to create new connection")
finally:
with self._lock:
self._scheduled_for_creation -= 1
def _add_conn_if_under_max(self):
max_conns = self._session.cluster.get_max_connections_per_host(self.host_distance)
with self._lock:
if self.is_shutdown:
return False
if self.open_count >= max_conns:
return False
self.open_count += 1
log.debug("Going to open new connection to host %s", self.host)
try:
conn = self._session.cluster.connection_factory(self.host.address)
if self._session.keyspace:
conn.set_keyspace_blocking(self._session.keyspace)
self._next_trash_allowed_at = time.time() + _MIN_TRASH_INTERVAL
with self._lock:
new_connections = self._connections[:] + [conn]
self._connections = new_connections
log.debug("Added new connection (%s) to pool for host %s, signaling availablility",
id(conn), self.host)
self._signal_available_conn()
return True
except (ConnectionException, socket.error) as exc:
log.warning("Failed to add new connection to pool for host %s: %s", self.host, exc)
with self._lock:
self.open_count -= 1
if self._session.cluster.signal_connection_failure(self.host, exc, is_host_addition=False):
self.shutdown()
return False
except AuthenticationFailed:
with self._lock:
self.open_count -= 1
return False
def _await_available_conn(self, timeout):
with self._conn_available_condition:
self._conn_available_condition.wait(timeout)
def _signal_available_conn(self):
with self._conn_available_condition:
self._conn_available_condition.notify()
def _signal_all_available_conn(self):
with self._conn_available_condition:
self._conn_available_condition.notify_all()
def _wait_for_conn(self, timeout):
start = time.time()
remaining = timeout
while remaining > 0:
# wait on our condition for the possibility that a connection
# is useable
self._await_available_conn(remaining)
# self.shutdown() may trigger the above Condition
if self.is_shutdown:
raise ConnectionException("Pool is shutdown")
conns = self._connections
if conns:
least_busy = min(conns, key=lambda c: c.in_flight)
with least_busy.lock:
if least_busy.in_flight < least_busy.max_request_id:
least_busy.in_flight += 1
return least_busy, least_busy.get_request_id()
remaining = timeout - (time.time() - start)
raise NoConnectionsAvailable()
def return_connection(self, connection):
with connection.lock:
connection.in_flight -= 1
in_flight = connection.in_flight
if connection.is_defunct or connection.is_closed:
log.debug("Defunct or closed connection (%s) returned to pool, potentially "
"marking host %s as down", id(connection), self.host)
is_down = self._session.cluster.signal_connection_failure(
self.host, connection.last_error, is_host_addition=False)
if is_down:
self.shutdown()
else:
self._replace(connection)
else:
if connection in self._trash:
with connection.lock:
if connection.in_flight == 0:
with self._lock:
if connection in self._trash:
self._trash.remove(connection)
log.debug("Closing trashed connection (%s) to %s", id(connection), self.host)
connection.close()
return
core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
min_reqs = self._session.cluster.get_min_requests_per_connection(self.host_distance)
# we can use in_flight here without holding the connection lock
# because the fact that in_flight dipped below the min at some
# point is enough to start the trashing procedure
if len(self._connections) > core_conns and in_flight <= min_reqs and \
time.time() >= self._next_trash_allowed_at:
self._maybe_trash_connection(connection)
else:
self._signal_available_conn()
def _maybe_trash_connection(self, connection):
core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
did_trash = False
with self._lock:
if connection not in self._connections:
return
if self.open_count > core_conns:
did_trash = True
self.open_count -= 1
new_connections = self._connections[:]
new_connections.remove(connection)
self._connections = new_connections
with connection.lock:
if connection.in_flight == 0:
log.debug("Skipping trash and closing unused connection (%s) to %s", id(connection), self.host)
connection.close()
# skip adding it to the trash if we're already closing it
return
self._trash.add(connection)
if did_trash:
self._next_trash_allowed_at = time.time() + _MIN_TRASH_INTERVAL
log.debug("Trashed connection (%s) to %s", id(connection), self.host)
def _replace(self, connection):
should_replace = False
with self._lock:
if connection in self._connections:
new_connections = self._connections[:]
new_connections.remove(connection)
self._connections = new_connections
self.open_count -= 1
should_replace = True
if should_replace:
log.debug("Replacing connection (%s) to %s", id(connection), self.host)
def close_and_replace():
connection.close()
self._add_conn_if_under_max()
self._session.submit(close_and_replace)
else:
# just close it
log.debug("Closing connection (%s) to %s", id(connection), self.host)
connection.close()
def shutdown(self):
with self._lock:
if self.is_shutdown:
return
else:
self.is_shutdown = True
self._signal_all_available_conn()
for conn in self._connections:
conn.close()
self.open_count -= 1
for conn in self._trash:
conn.close()
def ensure_core_connections(self):
if self.is_shutdown:
return
core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
with self._lock:
to_create = core_conns - (len(self._connections) + self._scheduled_for_creation)
for i in range(to_create):
self._scheduled_for_creation += 1
self._session.submit(self._create_new_connection)
def _set_keyspace_for_all_conns(self, keyspace, callback):
"""
Asynchronously sets the keyspace for all connections. When all
connections have been set, `callback` will be called with two
arguments: this pool, and a list of any errors that occurred.
"""
remaining_callbacks = set(self._connections)
errors = []
if not remaining_callbacks:
callback(self, errors)
return
def connection_finished_setting_keyspace(conn, error):
self.return_connection(conn)
remaining_callbacks.remove(conn)
if error:
errors.append(error)
if not remaining_callbacks:
callback(self, errors)
for conn in self._connections:
conn.set_keyspace_async(keyspace, connection_finished_setting_keyspace)
def get_connections(self):
return self._connections
def get_state(self):
in_flights = [c.in_flight for c in self._connections]
return {'shutdown': self.is_shutdown, 'open_count': self.open_count, 'in_flights': in_flights}