| # |
| # Licensed to the Apache Software Foundation (ASF) under one or more |
| # contributor license agreements. See the NOTICE file distributed with |
| # this work for additional information regarding copyright ownership. |
| # The ASF licenses this file to You 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 module for caching state reads/writes in Beam applications.""" |
| from __future__ import absolute_import |
| |
| import collections |
| import logging |
| from threading import Lock |
| |
| |
| class StateCache(object): |
| """ Cache for Beam state access, scoped by state key and cache_token. |
| |
| For a given state_key, caches a (cache_token, value) tuple and allows to |
| a) read from the cache (get), |
| if the currently stored cache_token matches the provided |
| a) write to the cache (put), |
| storing the new value alongside with a cache token |
| c) append to the cache (extend), |
| if the currently stored cache_token matches the provided |
| |
| The operations on the cache are thread-safe for use by multiple workers. |
| |
| :arg max_entries The maximum number of entries to store in the cache. |
| TODO Memory-based caching: https://issues.apache.org/jira/browse/BEAM-8297 |
| """ |
| |
| def __init__(self, max_entries): |
| logging.info('Creating state cache with size %s', max_entries) |
| self._cache = self.LRUCache(max_entries, (None, None)) |
| self._lock = Lock() |
| |
| def get(self, state_key, cache_token): |
| assert cache_token and self.is_cache_enabled() |
| with self._lock: |
| token, value = self._cache.get(state_key) |
| return value if token == cache_token else None |
| |
| def put(self, state_key, cache_token, value): |
| assert cache_token and self.is_cache_enabled() |
| with self._lock: |
| return self._cache.put(state_key, (cache_token, value)) |
| |
| def extend(self, state_key, cache_token, elements): |
| assert cache_token and self.is_cache_enabled() |
| with self._lock: |
| token, value = self._cache.get(state_key) |
| if token in [cache_token, None]: |
| if value is None: |
| value = [] |
| value.extend(elements) |
| self._cache.put(state_key, (cache_token, value)) |
| else: |
| # Discard cached state if tokens do not match |
| self._cache.evict(state_key) |
| |
| def clear(self, state_key, cache_token): |
| assert cache_token and self.is_cache_enabled() |
| with self._lock: |
| token, _ = self._cache.get(state_key) |
| if token in [cache_token, None]: |
| self._cache.put(state_key, (cache_token, [])) |
| else: |
| # Discard cached state if tokens do not match |
| self._cache.evict(state_key) |
| |
| def evict(self, state_key): |
| assert self.is_cache_enabled() |
| with self._lock: |
| self._cache.evict(state_key) |
| |
| def evict_all(self): |
| with self._lock: |
| self._cache.evict_all() |
| |
| def is_cache_enabled(self): |
| return self._cache._max_entries > 0 |
| |
| def __len__(self): |
| return len(self._cache) |
| |
| class LRUCache(object): |
| |
| def __init__(self, max_entries, default_entry): |
| self._max_entries = max_entries |
| self._default_entry = default_entry |
| self._cache = collections.OrderedDict() |
| |
| def get(self, key): |
| value = self._cache.pop(key, self._default_entry) |
| if value != self._default_entry: |
| self._cache[key] = value |
| return value |
| |
| def put(self, key, value): |
| self._cache[key] = value |
| while len(self._cache) > self._max_entries: |
| self._cache.popitem(last=False) |
| |
| def evict(self, key): |
| self._cache.pop(key, self._default_entry) |
| |
| def evict_all(self): |
| self._cache.clear() |
| |
| def __len__(self): |
| return len(self._cache) |