mirror of
https://git.anonymousland.org/anonymousland/synapse-product.git
synced 2024-12-22 11:04:58 -05:00
151 lines
4.9 KiB
Python
151 lines
4.9 KiB
Python
# Copyright 2021 The Matrix.org Foundation C.I.C.
|
|
#
|
|
# 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.
|
|
|
|
"""A circular doubly linked list implementation.
|
|
"""
|
|
|
|
import threading
|
|
from typing import Generic, Optional, Type, TypeVar
|
|
|
|
P = TypeVar("P")
|
|
LN = TypeVar("LN", bound="ListNode")
|
|
|
|
|
|
class ListNode(Generic[P]):
|
|
"""A node in a circular doubly linked list, with an (optional) reference to
|
|
a cache entry.
|
|
|
|
The reference should only be `None` for the root node or if the node has
|
|
been removed from the list.
|
|
"""
|
|
|
|
# A lock to protect mutating the list prev/next pointers.
|
|
_LOCK = threading.Lock()
|
|
|
|
# We don't use attrs here as in py3.6 you can't have `attr.s(slots=True)`
|
|
# and inherit from `Generic` for some reason
|
|
__slots__ = [
|
|
"cache_entry",
|
|
"prev_node",
|
|
"next_node",
|
|
]
|
|
|
|
def __init__(self, cache_entry: Optional[P] = None) -> None:
|
|
self.cache_entry = cache_entry
|
|
self.prev_node: Optional[ListNode[P]] = None
|
|
self.next_node: Optional[ListNode[P]] = None
|
|
|
|
@classmethod
|
|
def create_root_node(cls: Type["ListNode[P]"]) -> "ListNode[P]":
|
|
"""Create a new linked list by creating a "root" node, which is a node
|
|
that has prev_node/next_node pointing to itself and no associated cache
|
|
entry.
|
|
"""
|
|
root = cls()
|
|
root.prev_node = root
|
|
root.next_node = root
|
|
return root
|
|
|
|
@classmethod
|
|
def insert_after(
|
|
cls: Type[LN],
|
|
cache_entry: P,
|
|
node: "ListNode[P]",
|
|
) -> LN:
|
|
"""Create a new list node that is placed after the given node.
|
|
|
|
Args:
|
|
cache_entry: The associated cache entry.
|
|
node: The existing node in the list to insert the new entry after.
|
|
"""
|
|
new_node = cls(cache_entry)
|
|
with cls._LOCK:
|
|
new_node._refs_insert_after(node)
|
|
return new_node
|
|
|
|
def remove_from_list(self) -> None:
|
|
"""Remove this node from the list."""
|
|
with self._LOCK:
|
|
self._refs_remove_node_from_list()
|
|
|
|
# We drop the reference to the cache entry to break the reference cycle
|
|
# between the list node and cache entry, allowing the two to be dropped
|
|
# immediately rather than at the next GC.
|
|
self.cache_entry = None
|
|
|
|
def move_after(self, node: "ListNode[P]") -> None:
|
|
"""Move this node from its current location in the list to after the
|
|
given node.
|
|
"""
|
|
with self._LOCK:
|
|
# We assert that both this node and the target node is still "alive".
|
|
assert self.prev_node
|
|
assert self.next_node
|
|
assert node.prev_node
|
|
assert node.next_node
|
|
|
|
assert self is not node
|
|
|
|
# Remove self from the list
|
|
self._refs_remove_node_from_list()
|
|
|
|
# Insert self back into the list, after target node
|
|
self._refs_insert_after(node)
|
|
|
|
def _refs_remove_node_from_list(self) -> None:
|
|
"""Internal method to *just* remove the node from the list, without
|
|
e.g. clearing out the cache entry.
|
|
"""
|
|
if self.prev_node is None or self.next_node is None:
|
|
# We've already been removed from the list.
|
|
return
|
|
|
|
prev_node = self.prev_node
|
|
next_node = self.next_node
|
|
|
|
prev_node.next_node = next_node
|
|
next_node.prev_node = prev_node
|
|
|
|
# We set these to None so that we don't get circular references,
|
|
# allowing us to be dropped without having to go via the GC.
|
|
self.prev_node = None
|
|
self.next_node = None
|
|
|
|
def _refs_insert_after(self, node: "ListNode[P]") -> None:
|
|
"""Internal method to insert the node after the given node."""
|
|
|
|
# This method should only be called when we're not already in the list.
|
|
assert self.prev_node is None
|
|
assert self.next_node is None
|
|
|
|
# We expect the given node to be in the list and thus have valid
|
|
# prev/next refs.
|
|
assert node.next_node
|
|
assert node.prev_node
|
|
|
|
prev_node = node
|
|
next_node = node.next_node
|
|
|
|
self.prev_node = prev_node
|
|
self.next_node = next_node
|
|
|
|
prev_node.next_node = self
|
|
next_node.prev_node = self
|
|
|
|
def get_cache_entry(self) -> Optional[P]:
|
|
"""Get the cache entry, returns None if this is the root node (i.e.
|
|
cache_entry is None) or if the entry has been dropped.
|
|
"""
|
|
return self.cache_entry
|