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# Copyright 2014 Mirantis Inc
# All Rights Reserved.
#
# 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.
"""Thread-safe connection pool for python-memcached."""
# NOTE(yorik-sar): this file is copied between keystone and keystonemiddleware
# and should be kept in sync until we can use external library for this.
import collections
import contextlib
import itertools
import logging
import threading
import time
import memcache
from oslo_log import log
from six.moves import queue, zip
from keystone import exception
from keystone.i18n import _
LOG = log.getLogger(__name__)
class _MemcacheClient(memcache.Client):
"""Thread global memcache client
As client is inherited from threading.local we have to restore object
methods overloaded by threading.local so we can reuse clients in
different threads
"""
__delattr__ = object.__delattr__
__getattribute__ = object.__getattribute__
__new__ = object.__new__
__setattr__ = object.__setattr__
def __del__(self):
pass
_PoolItem = collections.namedtuple('_PoolItem', ['ttl', 'connection'])
class ConnectionPool(queue.Queue):
"""Base connection pool class
This class implements the basic connection pool logic as an abstract base
class.
"""
def __init__(self, maxsize, unused_timeout, conn_get_timeout=None):
"""Initialize the connection pool.
:param maxsize: maximum number of client connections for the pool
:type maxsize: int
:param unused_timeout: idle time to live for unused clients (in
seconds). If a client connection object has been
in the pool and idle for longer than the
unused_timeout, it will be reaped. This is to
ensure resources are released as utilization
goes down.
:type unused_timeout: int
:param conn_get_timeout: maximum time in seconds to wait for a
connection. If set to `None` timeout is
indefinite.
:type conn_get_timeout: int
"""
# super() cannot be used here because Queue in stdlib is an
# old-style class
queue.Queue.__init__(self, maxsize)
self._unused_timeout = unused_timeout
self._connection_get_timeout = conn_get_timeout
self._acquired = 0
def _create_connection(self):
"""Returns a connection instance.
This is called when the pool needs another instance created.
:returns: a new connection instance
"""
raise NotImplementedError
def _destroy_connection(self, conn):
"""Destroy and cleanup a connection instance.
This is called when the pool wishes to get rid of an existing
connection. This is the opportunity for a subclass to free up
resources and cleaup after itself.
:param conn: the connection object to destroy
"""
raise NotImplementedError
def _debug_logger(self, msg, *args, **kwargs):
if LOG.isEnabledFor(logging.DEBUG):
thread_id = threading.current_thread().ident
args = (id(self), thread_id) + args
prefix = 'Memcached pool %s, thread %s: '
LOG.debug(prefix + msg, *args, **kwargs)
@contextlib.contextmanager
def acquire(self):
self._debug_logger('Acquiring connection')
try:
conn = self.get(timeout=self._connection_get_timeout)
except queue.Empty:
raise exception.UnexpectedError(
_('Unable to get a connection from pool id %(id)s after '
'%(seconds)s seconds.') %
{'id': id(self), 'seconds': self._connection_get_timeout})
self._debug_logger('Acquired connection %s', id(conn))
try:
yield conn
finally:
self._debug_logger('Releasing connection %s', id(conn))
self._drop_expired_connections()
try:
# super() cannot be used here because Queue in stdlib is an
# old-style class
queue.Queue.put(self, conn, block=False)
except queue.Full:
self._debug_logger('Reaping exceeding connection %s', id(conn))
self._destroy_connection(conn)
def _qsize(self):
if self.maxsize:
return self.maxsize - self._acquired
else:
# A value indicating there is always a free connection
# if maxsize is None or 0
return 1
# NOTE(dstanek): stdlib and eventlet Queue implementations
# have different names for the qsize method. This ensures
# that we override both of them.
if not hasattr(queue.Queue, '_qsize'):
qsize = _qsize
def _get(self):
if self.queue:
conn = self.queue.pop().connection
else:
conn = self._create_connection()
self._acquired += 1
return conn
def _drop_expired_connections(self):
"""Drop all expired connections from the right end of the queue."""
now = time.time()
while self.queue and self.queue[0].ttl < now:
conn = self.queue.popleft().connection
self._debug_logger('Reaping connection %s', id(conn))
self._destroy_connection(conn)
def _put(self, conn):
self.queue.append(_PoolItem(
ttl=time.time() + self._unused_timeout,
connection=conn,
))
self._acquired -= 1
class MemcacheClientPool(ConnectionPool):
def __init__(self, urls, arguments, **kwargs):
# super() cannot be used here because Queue in stdlib is an
# old-style class
ConnectionPool.__init__(self, **kwargs)
self.urls = urls
self._arguments = arguments
# NOTE(morganfainberg): The host objects expect an int for the
# deaduntil value. Initialize this at 0 for each host with 0 indicating
# the host is not dead.
self._hosts_deaduntil = [0] * len(urls)
def _create_connection(self):
return _MemcacheClient(self.urls, **self._arguments)
def _destroy_connection(self, conn):
conn.disconnect_all()
def _get(self):
# super() cannot be used here because Queue in stdlib is an
# old-style class
conn = ConnectionPool._get(self)
try:
# Propagate host state known to us to this client's list
now = time.time()
for deaduntil, host in zip(self._hosts_deaduntil, conn.servers):
if deaduntil > now and host.deaduntil <= now:
host.mark_dead('propagating death mark from the pool')
host.deaduntil = deaduntil
except Exception:
# We need to be sure that connection doesn't leak from the pool.
# This code runs before we enter context manager's try-finally
# block, so we need to explicitly release it here.
# super() cannot be used here because Queue in stdlib is an
# old-style class
ConnectionPool._put(self, conn)
raise
return conn
def _put(self, conn):
try:
# If this client found that one of the hosts is dead, mark it as
# such in our internal list
now = time.time()
for i, host in zip(itertools.count(), conn.servers):
deaduntil = self._hosts_deaduntil[i]
# Do nothing if we already know this host is dead
if deaduntil <= now:
if host.deaduntil > now:
self._hosts_deaduntil[i] = host.deaduntil
self._debug_logger(
'Marked host %s dead until %s',
self.urls[i], host.deaduntil)
else:
self._hosts_deaduntil[i] = 0
# If all hosts are dead we should forget that they're dead. This
# way we won't get completely shut off until dead_retry seconds
# pass, but will be checking servers as frequent as we can (over
# way smaller socket_timeout)
if all(deaduntil > now for deaduntil in self._hosts_deaduntil):
self._debug_logger('All hosts are dead. Marking them as live.')
self._hosts_deaduntil[:] = [0] * len(self._hosts_deaduntil)
finally:
# super() cannot be used here because Queue in stdlib is an
# old-style class
ConnectionPool._put(self, conn)
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