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# Copyright 2013 Red Hat, 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.
import abc
import collections
import threading
import six
@six.add_metaclass(abc.ABCMeta)
class Pool(object):
"""A thread-safe object pool.
Modelled after the eventlet.pools.Pool interface, but designed to be safe
when using native threads without the GIL.
Resizing is not supported.
"""
def __init__(self, max_size=4):
super(Pool, self).__init__()
self._max_size = max_size
self._current_size = 0
self._cond = threading.Condition()
self._items = collections.deque()
def put(self, item):
"""Return an item to the pool."""
with self._cond:
self._items.appendleft(item)
self._cond.notify()
def get(self):
"""Return an item from the pool, when one is available.
This may cause the calling thread to block.
"""
with self._cond:
while True:
try:
return self._items.popleft()
except IndexError:
pass
if self._current_size < self._max_size:
self._current_size += 1
break
# FIXME(markmc): timeout needed to allow keyboard interrupt
# http://bugs.python.org/issue8844
self._cond.wait(timeout=1)
# We've grabbed a slot and dropped the lock, now do the creation
try:
return self.create()
except Exception:
with self._cond:
self._current_size -= 1
raise
def iter_free(self):
"""Iterate over free items."""
with self._cond:
while True:
try:
yield self._items.popleft()
except IndexError:
break
@abc.abstractmethod
def create(self):
"""Construct a new item."""
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