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# Copyright 2016 OpenMarket Ltd
#
# 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 logging
from typing import Generic, Hashable, List, Set, TypeVar
import attr
logger = logging.getLogger(__name__)
T = TypeVar("T", bound=Hashable)
@attr.s(slots=True, frozen=True, auto_attribs=True)
class _Entry(Generic[T]):
end_key: int
elements: Set[T] = attr.Factory(set)
class WheelTimer(Generic[T]):
"""Stores arbitrary objects that will be returned after their timers have
expired.
"""
def __init__(self, bucket_size: int = 5000) -> None:
"""
Args:
bucket_size: Size of buckets in ms. Corresponds roughly to the
accuracy of the timer.
"""
self.bucket_size: int = bucket_size
self.entries: List[_Entry[T]] = []
self.current_tick: int = 0
def insert(self, now: int, obj: T, then: int) -> None:
"""Inserts object into timer.
Args:
now: Current time in msec
obj: Object to be inserted
then: When to return the object strictly after.
"""
then_key = int(then / self.bucket_size) + 1
now_key = int(now / self.bucket_size)
if self.entries:
min_key = self.entries[0].end_key
max_key = self.entries[-1].end_key
if min_key < now_key - 10:
# If we have ten buckets that are due and still nothing has
# called `fetch()` then we likely have a bug that is causing a
# memory leak.
logger.warning(
"Inserting into a wheel timer that hasn't been read from recently. Item: %s",
obj,
)
if then_key <= max_key:
# The max here is to protect against inserts for times in the past
self.entries[max(min_key, then_key) - min_key].elements.add(obj)
return
next_key = now_key + 1
if self.entries:
last_key = self.entries[-1].end_key
else:
last_key = next_key
# Handle the case when `then` is in the past and `entries` is empty.
then_key = max(last_key, then_key)
# Add empty entries between the end of the current list and when we want
# to insert. This ensures there are no gaps.
self.entries.extend(_Entry(key) for key in range(last_key, then_key + 1))
self.entries[-1].elements.add(obj)
def fetch(self, now: int) -> List[T]:
"""Fetch any objects that have timed out
Args:
now (ms): Current time in msec
Returns:
list: List of objects that have timed out
"""
now_key = int(now / self.bucket_size)
ret: List[T] = []
while self.entries and self.entries[0].end_key <= now_key:
ret.extend(self.entries.pop(0).elements)
return ret
def __len__(self) -> int:
return sum(len(entry.elements) for entry in self.entries)
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