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Allow for ignoring some arguments when caching. (#12189)

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* `@cached` can now take an `uncached_args` which is an iterable of names to not use in the cache key.
* Requires `@cached`, @cachedList` and `@lru_cache` to use keyword arguments for clarity.
* Asserts that keyword-only arguments in cached functions are not accepted. (I tested this briefly and I don't believe this works properly.)
This commit is contained in:
Patrick Cloke 2022-03-09 13:07:41 -05:00 • committed by GitHub
parent 032688854b
commit 690cb4f3b3
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4 changed files with 142 additions and 21 deletions
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74
synapse/util/caches/descriptors.py
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@ -20,6 +20,7 @@ from typing import (
Any,
Awaitable,
Callable,
Collection,
Dict,
Generic,
Hashable,
@ -69,6 +70,7 @@ class _CacheDescriptorBase:
self,
orig: Callable[..., Any],
num_args: Optional[int],
uncached_args: Optional[Collection[str]] = None,
cache_context: bool = False,
):
self.orig = orig
@ -76,6 +78,13 @@ class _CacheDescriptorBase:
arg_spec = inspect.getfullargspec(orig)
all_args = arg_spec.args
# There's no reason that keyword-only arguments couldn't be supported,
# but right now they're buggy so do not allow them.
if arg_spec.kwonlyargs:
raise ValueError(
"_CacheDescriptorBase does not support keyword-only arguments."
)
if "cache_context" in all_args:
if not cache_context:
raise ValueError(
@ -88,6 +97,9 @@ class _CacheDescriptorBase:
" named `cache_context`"
)
if num_args is not None and uncached_args is not None:
raise ValueError("Cannot provide both num_args and uncached_args")
if num_args is None:
num_args = len(all_args) - 1
if cache_context:
@ -105,6 +117,12 @@ class _CacheDescriptorBase:
# list of the names of the args used as the cache key
self.arg_names = all_args[1 : num_args + 1]
# If there are args to not cache on, filter them out (and fix the size of num_args).
if uncached_args is not None:
include_arg_in_cache_key = [n not in uncached_args for n in self.arg_names]
else:
include_arg_in_cache_key = [True] * len(self.arg_names)
# self.arg_defaults is a map of arg name to its default value for each
# argument that has a default value
if arg_spec.defaults:
@ -119,8 +137,8 @@ class _CacheDescriptorBase:
self.add_cache_context = cache_context
self.cache_key_builder = get_cache_key_builder(
self.arg_names, self.arg_defaults
self.cache_key_builder = _get_cache_key_builder(
self.arg_names, include_arg_in_cache_key, self.arg_defaults
)
@ -130,8 +148,7 @@ class _LruCachedFunction(Generic[F]):
def lru_cache(
max_entries: int = 1000,
cache_context: bool = False,
*, max_entries: int = 1000, cache_context: bool = False
) -> Callable[[F], _LruCachedFunction[F]]:
"""A method decorator that applies a memoizing cache around the function.
@ -186,7 +203,9 @@ class LruCacheDescriptor(_CacheDescriptorBase):
max_entries: int = 1000,
cache_context: bool = False,
):
super().__init__(orig, num_args=None, cache_context=cache_context)
super().__init__(
orig, num_args=None, uncached_args=None, cache_context=cache_context
)
self.max_entries = max_entries
def __get__(self, obj: Optional[Any], owner: Optional[Type]) -> Callable[..., Any]:
@ -260,6 +279,9 @@ class DeferredCacheDescriptor(_CacheDescriptorBase):
num_args: number of positional arguments (excluding ``self`` and
``cache_context``) to use as cache keys. Defaults to all named
args of the function.
uncached_args: a list of argument names to not use as the cache key.
(``self`` and ``cache_context`` are always ignored.) Cannot be used
with num_args.
tree:
cache_context:
iterable:
@ -273,12 +295,18 @@ class DeferredCacheDescriptor(_CacheDescriptorBase):
orig: Callable[..., Any],
max_entries: int = 1000,
num_args: Optional[int] = None,
uncached_args: Optional[Collection[str]] = None,
tree: bool = False,
cache_context: bool = False,
iterable: bool = False,
prune_unread_entries: bool = True,
):
super().__init__(orig, num_args=num_args, cache_context=cache_context)
super().__init__(
orig,
num_args=num_args,
uncached_args=uncached_args,
cache_context=cache_context,
)
if tree and self.num_args < 2:
raise RuntimeError(
@ -369,7 +397,7 @@ class DeferredCacheListDescriptor(_CacheDescriptorBase):
but including list_name) to use as cache keys. Defaults to all
named args of the function.
"""
super().__init__(orig, num_args=num_args)
super().__init__(orig, num_args=num_args, uncached_args=None)
self.list_name = list_name
@ -530,8 +558,10 @@ class _CacheContext:
def cached(
*,
max_entries: int = 1000,
num_args: Optional[int] = None,
uncached_args: Optional[Collection[str]] = None,
tree: bool = False,
cache_context: bool = False,
iterable: bool = False,
@ -541,6 +571,7 @@ def cached(
orig,
max_entries=max_entries,
num_args=num_args,
uncached_args=uncached_args,
tree=tree,
cache_context=cache_context,
iterable=iterable,
@ -551,7 +582,7 @@ def cached(
def cachedList(
cached_method_name: str, list_name: str, num_args: Optional[int] = None
*, cached_method_name: str, list_name: str, num_args: Optional[int] = None
) -> Callable[[F], _CachedFunction[F]]:
"""Creates a descriptor that wraps a function in a `CacheListDescriptor`.
@ -590,13 +621,16 @@ def cachedList(
return cast(Callable[[F], _CachedFunction[F]], func)
def get_cache_key_builder(
param_names: Sequence[str], param_defaults: Mapping[str, Any]
def _get_cache_key_builder(
param_names: Sequence[str],
include_params: Sequence[bool],
param_defaults: Mapping[str, Any],
) -> Callable[[Sequence[Any], Mapping[str, Any]], CacheKey]:
"""Construct a function which will build cache keys suitable for a cached function
Args:
param_names: list of formal parameter names for the cached function
include_params: list of bools of whether to include the parameter name in the cache key
param_defaults: a mapping from parameter name to default value for that param
Returns:
@ -608,6 +642,7 @@ def get_cache_key_builder(
if len(param_names) == 1:
nm = param_names[0]
assert include_params[0] is True
def get_cache_key(args: Sequence[Any], kwargs: Mapping[str, Any]) -> CacheKey:
if nm in kwargs:
@ -620,13 +655,18 @@ def get_cache_key_builder(
else:
def get_cache_key(args: Sequence[Any], kwargs: Mapping[str, Any]) -> CacheKey:
return tuple(_get_cache_key_gen(param_names, param_defaults, args, kwargs))
return tuple(
_get_cache_key_gen(
param_names, include_params, param_defaults, args, kwargs
)
)
return get_cache_key
def _get_cache_key_gen(
param_names: Iterable[str],
include_params: Iterable[bool],
param_defaults: Mapping[str, Any],
args: Sequence[Any],
kwargs: Mapping[str, Any],
@ -637,16 +677,18 @@ def _get_cache_key_gen(
This is essentially the same operation as `inspect.getcallargs`, but optimised so
that we don't need to inspect the target function for each call.
"""
# We loop through each arg name, looking up if its in the `kwargs`,
# otherwise using the next argument in `args`. If there are no more
# args then we try looking the arg name up in the defaults.
pos = 0
for nm in param_names:
for nm, inc in zip(param_names, include_params):
if nm in kwargs:
yield kwargs[nm]
if inc:
yield kwargs[nm]
elif pos < len(args):
yield args[pos]
if inc:
yield args[pos]
pos += 1
else:
yield param_defaults[nm]
if inc:
yield param_defaults[nm]