81 lines
3 KiB
Diff
81 lines
3 KiB
Diff
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
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index 5ac2530a6..d803d62b8 100644
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--- a/synapse/util/caches/descriptors.py
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+++ b/synapse/util/caches/descriptors.py
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@@ -17,8 +17,8 @@ import functools
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import inspect
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import logging
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import threading
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-from collections import namedtuple
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-from typing import Any, cast
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+from typing import Any, Tuple, Union, cast
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+from weakref import WeakValueDictionary
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from six import itervalues
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@@ -38,6 +38,8 @@ from . import register_cache
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logger = logging.getLogger(__name__)
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+CacheKey = Union[Tuple, Any]
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+
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class _CachedFunction(Protocol):
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invalidate = None # type: Any
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@@ -430,7 +432,7 @@ class CacheDescriptor(_CacheDescriptorBase):
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# Add our own `cache_context` to argument list if the wrapped function
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# has asked for one
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if self.add_cache_context:
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- kwargs["cache_context"] = _CacheContext(cache, cache_key)
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+ kwargs["cache_context"] = _CacheContext.get_instance(cache, cache_key)
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try:
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cached_result_d = cache.get(cache_key, callback=invalidate_callback)
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@@ -625,14 +627,38 @@ class CacheListDescriptor(_CacheDescriptorBase):
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return wrapped
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-class _CacheContext(namedtuple("_CacheContext", ("cache", "key"))):
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- # We rely on _CacheContext implementing __eq__ and __hash__ sensibly,
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- # which namedtuple does for us (i.e. two _CacheContext are the same if
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- # their caches and keys match). This is important in particular to
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- # dedupe when we add callbacks to lru cache nodes, otherwise the number
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- # of callbacks would grow.
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- def invalidate(self):
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- self.cache.invalidate(self.key)
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+class _CacheContext:
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+ """Holds cache information from the cached function higher in the calling order.
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+
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+ Can be used to invalidate the higher level cache entry if something changes
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+ on a lower level.
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+ """
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+
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+ _cache_context_objects = (
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+ WeakValueDictionary()
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+ ) # type: WeakValueDictionary[Tuple[Cache, CacheKey], _CacheContext]
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+
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+ def __init__(self, cache, cache_key): # type: (Cache, CacheKey) -> None
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+ self._cache = cache
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+ self._cache_key = cache_key
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+
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+ def invalidate(self): # type: () -> None
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+ """Invalidates the cache entry referred to by the context."""
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+ self._cache.invalidate(self._cache_key)
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+
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+ @classmethod
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+ def get_instance(cls, cache, cache_key): # type: (Cache, CacheKey) -> _CacheContext
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+ """Returns an instance constructed with the given arguments.
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+
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+ A new instance is only created if none already exists.
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+ """
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+
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+ # We make sure there are no identical _CacheContext instances. This is
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+ # important in particular to dedupe when we add callbacks to lru cache
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+ # nodes, otherwise the number of callbacks would grow.
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+ return cls._cache_context_objects.setdefault(
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+ (cache, cache_key), cls(cache, cache_key)
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+ )
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def cached(
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