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# Copyright 2015, 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
import time
from typing import Any, Callable, Dict, Generic, Tuple, TypeVar, Union
import attr
from sortedcontainers import SortedList
from synapse.util.caches import register_cache
logger = logging.getLogger(__name__)
SENTINEL: Any = object()
T = TypeVar("T")
KT = TypeVar("KT")
VT = TypeVar("VT")
class TTLCache(Generic[KT, VT]):
"""A key/value cache implementation where each entry has its own TTL"""
def __init__(self, cache_name: str, timer: Callable[[], float] = time.time):
# map from key to _CacheEntry
self._data: Dict[KT, _CacheEntry] = {}
# the _CacheEntries, sorted by expiry time
self._expiry_list: SortedList[_CacheEntry] = SortedList()
self._timer = timer
self._metrics = register_cache("ttl", cache_name, self, resizable=False)
def set(self, key: KT, value: VT, ttl: float) -> None:
"""Add/update an entry in the cache
Args:
key: key for this entry
value: value for this entry
ttl: TTL for this entry, in seconds
"""
expiry = self._timer() + ttl
self.expire()
e = self._data.pop(key, SENTINEL)
if e is not SENTINEL:
assert isinstance(e, _CacheEntry)
self._expiry_list.remove(e)
entry = _CacheEntry(expiry_time=expiry, ttl=ttl, key=key, value=value)
self._data[key] = entry
self._expiry_list.add(entry)
def get(self, key: KT, default: T = SENTINEL) -> Union[VT, T]:
"""Get a value from the cache
Args:
key: key to look up
default: default value to return, if key is not found. If not set, and the
key is not found, a KeyError will be raised
Returns:
value from the cache, or the default
"""
self.expire()
e = self._data.get(key, SENTINEL)
if e is SENTINEL:
self._metrics.inc_misses()
if default is SENTINEL:
raise KeyError(key)
return default
assert isinstance(e, _CacheEntry)
self._metrics.inc_hits()
return e.value
def get_with_expiry(self, key: KT) -> Tuple[VT, float, float]:
"""Get a value, and its expiry time, from the cache
Args:
key: key to look up
Returns:
A tuple of the value from the cache, the expiry time and the TTL
Raises:
KeyError if the entry is not found
"""
self.expire()
try:
e = self._data[key]
except KeyError:
self._metrics.inc_misses()
raise
self._metrics.inc_hits()
return e.value, e.expiry_time, e.ttl
def pop(self, key: KT, default: T = SENTINEL) -> Union[VT, T]:
"""Remove a value from the cache
If key is in the cache, remove it and return its value, else return default.
If default is not given and key is not in the cache, a KeyError is raised.
Args:
key: key to look up
default: default value to return, if key is not found. If not set, and the
key is not found, a KeyError will be raised
Returns:
value from the cache, or the default
"""
self.expire()
e = self._data.pop(key, SENTINEL)
if e is SENTINEL:
self._metrics.inc_misses()
if default is SENTINEL:
raise KeyError(key)
return default
assert isinstance(e, _CacheEntry)
self._expiry_list.remove(e)
self._metrics.inc_hits()
return e.value
def __getitem__(self, key: KT) -> VT:
return self.get(key)
def __delitem__(self, key: KT) -> None:
self.pop(key)
def __contains__(self, key: KT) -> bool:
return key in self._data
def __len__(self) -> int:
self.expire()
return len(self._data)
def expire(self) -> None:
"""Run the expiry on the cache. Any entries whose expiry times are due will
be removed
"""
now = self._timer()
while self._expiry_list:
first_entry = self._expiry_list[0]
if first_entry.expiry_time - now > 0.0:
break
del self._data[first_entry.key]
del self._expiry_list[0]
@attr.s(frozen=True, slots=True, auto_attribs=True)
class _CacheEntry: # Should be Generic[KT, VT]. See python-attrs/attrs#313
"""TTLCache entry"""
# expiry_time is the first attribute, so that entries are sorted by expiry.
expiry_time: float
ttl: float
key: Any # should be KT
value: Any # should be VT
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