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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 time
from six.moves import queue
from keystonemiddleware.i18n import _LC
_PoolItem = collections.namedtuple('_PoolItem', ['ttl', 'connection'])
class ConnectionGetTimeoutException(Exception):
pass
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
"""
queue.Queue.__init__(self, maxsize)
self._unused_timeout = unused_timeout
self._connection_get_timeout = conn_get_timeout
self._acquired = 0
self._LOG = logging.getLogger(__name__)
def _create_connection(self):
raise NotImplementedError
def _destroy_connection(self, conn):
raise NotImplementedError
@contextlib.contextmanager
def acquire(self):
try:
conn = self.get(timeout=self._connection_get_timeout)
except queue.Empty:
self._LOG.critical(_LC('Unable to get a connection from pool id '
'%(id)s after %(seconds)s seconds.'),
{'id': id(self),
'seconds': self._connection_get_timeout})
raise ConnectionGetTimeoutException()
try:
yield conn
finally:
self.put(conn)
def _qsize(self):
return self.maxsize - self._acquired
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 _put(self, conn):
self.queue.append(_PoolItem(
ttl=time.time() + self._unused_timeout,
connection=conn,
))
self._acquired -= 1
# 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._destroy_connection(conn)
class MemcacheClientPool(ConnectionPool):
def __init__(self, urls, arguments, **kwargs):
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)
# NOTE(morganfainberg): Lazy import to allow middleware to work with
# python 3k even if memcache will not due to python 3k
# incompatibilities within the python-memcache library.
global memcache
import memcache
# This 'class' is taken from http://stackoverflow.com/a/22520633/238308
# Don't inherit client from threading.local so that we can reuse
# clients in different threads
MemcacheClient = type('_MemcacheClient', (object,),
dict(memcache.Client.__dict__))
self._memcache_client_class = MemcacheClient
def _create_connection(self):
return self._memcache_client_class(self._urls, **self._arguments)
def _destroy_connection(self, conn):
conn.disconnect_all()
def _get(self):
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
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, deaduntil, host in zip(itertools.count(),
self._hosts_deaduntil,
conn.servers):
# Do nothing if we already know this host is dead
if deaduntil <= now:
if host.deaduntil > now:
self._hosts_deaduntil[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._hosts_deaduntil[:] = [0] * len(self._hosts_deaduntil)
finally:
ConnectionPool._put(self, conn)
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