# Copyright 2018-2022 Streamlit Inc. # # 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. """Common cache logic shared by st.memo and st.singleton.""" import contextlib import functools import hashlib import inspect import threading import types from abc import abstractmethod from typing import Callable, List, Iterator, Tuple, Optional, Any, Union import streamlit as st from streamlit import util from streamlit.caching.cache_errors import CacheKeyNotFoundError from streamlit.logger import get_logger from .cache_errors import ( CacheType, CachedStFunctionWarning, UnhashableParamError, UnhashableTypeError, ) from .hashing import update_hash _LOGGER = get_logger(__name__) class Cache: """Function cache interface. Caches persist across script runs.""" @abstractmethod def read_value(self, value_key: str) -> Any: """Read a value from the cache. Raises ------ CacheKeyNotFoundError Raised if value_key is not in the cache. """ raise NotImplementedError @abstractmethod def write_value(self, value_key: str, value: Any) -> None: """Write a value to the cache, overwriting any existing value that uses the value_key. """ raise NotImplementedError @abstractmethod def clear(self) -> None: """Clear all values from this function cache.""" raise NotImplementedError class CachedFunction: """Encapsulates data for a cached function instance. CachedFunction instances are scoped to a single script run - they're not persistent. """ def __init__( self, func: types.FunctionType, show_spinner: bool, suppress_st_warning: bool ): self.func = func self.show_spinner = show_spinner self.suppress_st_warning = suppress_st_warning @property def cache_type(self) -> CacheType: raise NotImplementedError @property def call_stack(self) -> "CachedFunctionCallStack": raise NotImplementedError def get_function_cache(self, function_key: str) -> Cache: """Get or create the function cache for the given key.""" raise NotImplementedError def create_cache_wrapper(cached_func: CachedFunction) -> Callable[..., Any]: """Create a wrapper for a CachedFunction. This implements the common plumbing for both st.memo and st.singleton. """ func = cached_func.func function_key = _make_function_key(cached_func.cache_type, func) @functools.wraps(func) def wrapper(*args, **kwargs): """This function wrapper will only call the underlying function in the case of a cache miss. """ # Retrieve the function's cache object. We must do this inside the # wrapped function, because caches can be invalidated at any time. cache = cached_func.get_function_cache(function_key) name = func.__qualname__ if len(args) == 0 and len(kwargs) == 0: message = f"Running `{name}()`." else: message = f"Running `{name}(...)`." def get_or_create_cached_value(): # Generate the key for the cached value. This is based on the # arguments passed to the function. value_key = _make_value_key(cached_func.cache_type, func, *args, **kwargs) try: return_value = cache.read_value(value_key) _LOGGER.debug("Cache hit: %s", func) except CacheKeyNotFoundError: _LOGGER.debug("Cache miss: %s", func) with cached_func.call_stack.calling_cached_function(func): if cached_func.suppress_st_warning: with cached_func.call_stack.suppress_cached_st_function_warning(): return_value = func(*args, **kwargs) else: return_value = func(*args, **kwargs) cache.write_value(value_key, return_value) return return_value if cached_func.show_spinner: with st.spinner(message): return get_or_create_cached_value() else: return get_or_create_cached_value() def clear(): """Clear the wrapped function's associated cache.""" cache = cached_func.get_function_cache(function_key) cache.clear() # Mypy doesn't support declaring attributes of function objects, # so we have to suppress a warning here. We can remove this suppression # when this issue is resolved: https://github.com/python/mypy/issues/2087 wrapper.clear = clear # type: ignore return wrapper class CachedFunctionCallStack(threading.local): """A utility for warning users when they call `st` commands inside a cached function. Internally, this is just a counter that's incremented when we enter a cache function, and decremented when we exit. Data is stored in a thread-local object, so it's safe to use an instance of this class across multiple threads. """ def __init__(self, cache_type: CacheType): self._cached_func_stack: List[types.FunctionType] = [] self._suppress_st_function_warning = 0 self._cache_type = cache_type def __repr__(self) -> str: return util.repr_(self) @contextlib.contextmanager def calling_cached_function(self, func: types.FunctionType) -> Iterator[None]: self._cached_func_stack.append(func) try: yield finally: self._cached_func_stack.pop() @contextlib.contextmanager def suppress_cached_st_function_warning(self) -> Iterator[None]: self._suppress_st_function_warning += 1 try: yield finally: self._suppress_st_function_warning -= 1 assert self._suppress_st_function_warning >= 0 def maybe_show_cached_st_function_warning( self, dg: "st.delta_generator.DeltaGenerator", st_func_name: str ) -> None: """If appropriate, warn about calling st.foo inside @memo. DeltaGenerator's @_with_element and @_widget wrappers use this to warn the user when they're calling st.foo() from within a function that is wrapped in @st.cache. Parameters ---------- dg : DeltaGenerator The DeltaGenerator to publish the warning to. st_func_name : str The name of the Streamlit function that was called. """ if len(self._cached_func_stack) > 0 and self._suppress_st_function_warning <= 0: cached_func = self._cached_func_stack[-1] self._show_cached_st_function_warning(dg, st_func_name, cached_func) def _show_cached_st_function_warning( self, dg: "st.delta_generator.DeltaGenerator", st_func_name: str, cached_func: types.FunctionType, ) -> None: # Avoid infinite recursion by suppressing additional cached # function warnings from within the cached function warning. with self.suppress_cached_st_function_warning(): e = CachedStFunctionWarning(self._cache_type, st_func_name, cached_func) dg.exception(e) def _make_value_key( cache_type: CacheType, func: types.FunctionType, *args, **kwargs ) -> str: """Create the key for a value within a cache. This key is generated from the function's arguments. All arguments will be hashed, except for those named with a leading "_". Raises ------ StreamlitAPIException Raised (with a nicely-formatted explanation message) if we encounter an un-hashable arg. """ # Create a (name, value) list of all *args and **kwargs passed to the # function. arg_pairs: List[Tuple[Optional[str], Any]] = [] for arg_idx in range(len(args)): arg_name = _get_positional_arg_name(func, arg_idx) arg_pairs.append((arg_name, args[arg_idx])) for kw_name, kw_val in kwargs.items(): # **kwargs ordering is preserved, per PEP 468 # https://www.python.org/dev/peps/pep-0468/, so this iteration is # deterministic. arg_pairs.append((kw_name, kw_val)) # Create the hash from each arg value, except for those args whose name # starts with "_". (Underscore-prefixed args are deliberately excluded from # hashing.) args_hasher = hashlib.new("md5") for arg_name, arg_value in arg_pairs: if arg_name is not None and arg_name.startswith("_"): _LOGGER.debug("Not hashing %s because it starts with _", arg_name) continue try: update_hash( (arg_name, arg_value), hasher=args_hasher, cache_type=cache_type, ) except UnhashableTypeError as exc: raise UnhashableParamError(cache_type, func, arg_name, arg_value, exc) value_key = args_hasher.hexdigest() _LOGGER.debug("Cache key: %s", value_key) return value_key def _make_function_key(cache_type: CacheType, func: types.FunctionType) -> str: """Create the unique key for a function's cache. A function's key is stable across reruns of the app, and changes when the function's source code changes. """ func_hasher = hashlib.new("md5") # Include the function's __module__ and __qualname__ strings in the hash. # This means that two identical functions in different modules # will not share a hash; it also means that two identical *nested* # functions in the same module will not share a hash. update_hash( (func.__module__, func.__qualname__), hasher=func_hasher, cache_type=cache_type, ) # Include the function's source code in its hash. If the source code can't # be retrieved, fall back to the function's bytecode instead. source_code: Union[str, bytes] try: source_code = inspect.getsource(func) except OSError as e: _LOGGER.debug( "Failed to retrieve function's source code when building its key; falling back to bytecode. err={0}", e, ) source_code = func.__code__.co_code update_hash( source_code, hasher=func_hasher, cache_type=cache_type, ) cache_key = func_hasher.hexdigest() return cache_key def _get_positional_arg_name(func: types.FunctionType, arg_index: int) -> Optional[str]: """Return the name of a function's positional argument. If arg_index is out of range, or refers to a parameter that is not a named positional argument (e.g. an *args, **kwargs, or keyword-only param), return None instead. """ if arg_index < 0: return None params: List[inspect.Parameter] = list(inspect.signature(func).parameters.values()) if arg_index >= len(params): return None if params[arg_index].kind in ( inspect.Parameter.POSITIONAL_OR_KEYWORD, inspect.Parameter.POSITIONAL_ONLY, ): return params[arg_index].name return None