144 lines
4.4 KiB
Python
144 lines
4.4 KiB
Python
# Copyright 2016-2021 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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SENTINEL = object()
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class TreeCacheNode(dict):
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"""The type of nodes in our tree.
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Has its own type so we can distinguish it from real dicts that are stored at the
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leaves.
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"""
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pass
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class TreeCache:
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"""
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Tree-based backing store for LruCache. Allows subtrees of data to be deleted
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efficiently.
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Keys must be tuples.
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The data structure is a chain of TreeCacheNodes:
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root = {key_1: {key_2: _value}}
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"""
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def __init__(self) -> None:
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self.size: int = 0
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self.root = TreeCacheNode()
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def __setitem__(self, key, value) -> None:
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self.set(key, value)
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def __contains__(self, key) -> bool:
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return self.get(key, SENTINEL) is not SENTINEL
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def set(self, key, value) -> None:
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if isinstance(value, TreeCacheNode):
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# this would mean we couldn't tell where our tree ended and the value
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# started.
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raise ValueError("Cannot store TreeCacheNodes in a TreeCache")
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node = self.root
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for k in key[:-1]:
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next_node = node.get(k, SENTINEL)
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if next_node is SENTINEL:
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next_node = node[k] = TreeCacheNode()
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elif not isinstance(next_node, TreeCacheNode):
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# this suggests that the caller is not being consistent with its key
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# length.
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raise ValueError("value conflicts with an existing subtree")
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node = next_node
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node[key[-1]] = value
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self.size += 1
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def get(self, key, default=None):
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node = self.root
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for k in key[:-1]:
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node = node.get(k, None)
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if node is None:
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return default
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return node.get(key[-1], default)
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def clear(self) -> None:
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self.size = 0
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self.root = TreeCacheNode()
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def pop(self, key, default=None):
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"""Remove the given key, or subkey, from the cache
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Args:
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key: key or subkey to remove.
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default: value to return if key is not found
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Returns:
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If the key is not found, 'default'. If the key is complete, the removed
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value. If the key is partial, the TreeCacheNode corresponding to the part
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of the tree that was removed.
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"""
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if not isinstance(key, tuple):
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raise TypeError("The cache key must be a tuple not %r" % (type(key),))
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# a list of the nodes we have touched on the way down the tree
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nodes = []
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node = self.root
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for k in key[:-1]:
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node = node.get(k, None)
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if node is None:
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return default
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if not isinstance(node, TreeCacheNode):
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# we've gone off the end of the tree
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raise ValueError("pop() key too long")
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nodes.append(node) # don't add the root node
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popped = node.pop(key[-1], SENTINEL)
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if popped is SENTINEL:
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return default
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# working back up the tree, clear out any nodes that are now empty
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node_and_keys = list(zip(nodes, key))
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node_and_keys.reverse()
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node_and_keys.append((self.root, None))
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for i in range(len(node_and_keys) - 1):
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n, k = node_and_keys[i]
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if n:
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break
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# found an empty node: remove it from its parent, and loop.
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node_and_keys[i + 1][0].pop(k)
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cnt = sum(1 for _ in iterate_tree_cache_entry(popped))
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self.size -= cnt
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return popped
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def values(self):
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return iterate_tree_cache_entry(self.root)
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def __len__(self) -> int:
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return self.size
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def iterate_tree_cache_entry(d):
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"""Helper function to iterate over the leaves of a tree, i.e. a dict of that
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can contain dicts.
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"""
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if isinstance(d, TreeCacheNode):
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for value_d in d.values():
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yield from iterate_tree_cache_entry(value_d)
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else:
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yield d
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