| """Small per-instance LRU caches; no global references to fitted codecs.""" |
|
|
| from collections import OrderedDict |
| from collections.abc import MutableMapping |
| from threading import RLock |
|
|
|
|
| def cached_prefix_state(key, cache, initial, advance): |
| """Extend a cached parent prefix, replaying only when it was evicted.""" |
| if not key: |
| return initial |
| missing = object() |
| state = cache.get(key, missing) |
| if state is not missing: |
| return state |
| parent = key[:-1] |
| state = cache.get(parent, missing) |
| if state is missing: |
| state = initial |
| for token in parent: |
| state = advance(state, token) |
| if state is None: |
| break |
| cache[parent] = state |
| if state is not None: |
| state = advance(state, key[-1]) |
| cache[key] = state |
| return state |
|
|
|
|
| class BoundedCache(MutableMapping): |
| """Evict least-recently-used entries above a fixed capacity.""" |
|
|
| def __init__(self, capacity): |
| if type(capacity) is not int or capacity < 1: |
| raise ValueError("cache capacity must be a positive integer") |
| self.capacity = capacity |
| self._items = OrderedDict() |
| self._lock = RLock() |
|
|
| def __getitem__(self, key): |
| with self._lock: |
| value = self._items[key] |
| self._items.move_to_end(key) |
| return value |
|
|
| def __setitem__(self, key, value): |
| with self._lock: |
| self._items[key] = value |
| self._items.move_to_end(key) |
| while len(self._items) > self.capacity: |
| self._items.popitem(last=False) |
|
|
| def __delitem__(self, key): |
| with self._lock: |
| del self._items[key] |
|
|
| def __iter__(self): |
| with self._lock: |
| return iter(tuple(self._items)) |
|
|
| def __len__(self): |
| with self._lock: |
| return len(self._items) |
|
|
| def reserve(self, capacity): |
| """Raise the capacity so callers with a known working set stop thrashing.""" |
| if type(capacity) is not int or capacity < 1: |
| raise ValueError("cache capacity must be a positive integer") |
| with self._lock: |
| self.capacity = max(self.capacity, capacity) |
|
|
