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_idpool.py
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_idpool.py
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# Copyright 2016-2017 IBM Corp. 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.
"""
The :class:`~zhmcclient_mock.IdPool` class provides a pool of integer ID values
from a defined value range. This is used for example to manage automatically
allocated device numbers.
"""
from __future__ import absolute_import
__all__ = ['IdPool']
class IdPool(object):
"""
A pool of integer ID values from a defined value range.
The IDs can be allocated from and returned to the pool.
The pool is optimized for memory consumption, by only materializing ID
values as needed.
"""
def __init__(self, lowest, highest):
"""
Parameters:
lowest (integer): Lowest value of the ID value range.
highest (integer): Highest value of the ID value range.
"""
if lowest > highest:
raise ValueError("Lowest value %d is higher than highest %d" %
(lowest, highest))
# ID value range, using slice semantics (end points past the highest)
self._range_start = lowest
self._range_end = highest + 1
# The ID values in use.
self._used = set()
# Free pool: The ID values that are free and materialized.
self._free = set()
# Start of new free ID values to be materialized when the free pool is
# expanded.
self._expand_start = lowest
# Expansion chunk size: Number of new free ID values to be materialized
# when the free pool is expanded.
self._expand_len = 10
def _expand(self):
"""
Expand the free pool, if possible.
If out of capacity w.r.t. the defined ID value range, ValueError is
raised.
"""
assert not self._free # free pool is empty
expand_end = self._expand_start + self._expand_len
if expand_end > self._range_end:
# This happens if the size of the value range is not a multiple
# of the expansion chunk size.
expand_end = self._range_end
if self._expand_start == expand_end:
raise ValueError("Out of capacity in ID pool")
self._free = set(range(self._expand_start, expand_end))
self._expand_start = expand_end
def alloc(self):
"""
Allocate an ID value and return it.
Raises:
ValueError: Out of capacity in ID pool.
"""
if not self._free:
self._expand()
_id = self._free.pop()
self._used.add(_id)
return _id
def free(self, id):
# pylint: disable=redefined-builtin
"""
Free an ID value.
The ID value must be allocated.
Raises:
ValueError: ID value to be freed is not currently allocated.
"""
self._free_impl(id, fail_if_not_allocated=True)
def free_if_allocated(self, id):
# pylint: disable=redefined-builtin
"""
Free an ID value, if it is currently allocated.
If the specified ID value is not currently allocated, nothing happens.
"""
self._free_impl(id, fail_if_not_allocated=False)
def _free_impl(self, id, fail_if_not_allocated):
# pylint: disable=redefined-builtin
"""
Implementation of free.
"""
if id in self._used:
self._used.remove(id)
self._free.add(id)
elif fail_if_not_allocated:
raise ValueError("ID value to be freed is not currently "
"allocated: %d" % id)