Add type hints to DictionaryCache and TTLCache. (#9442)

2 files changed, 73 insertions, 44 deletions

diff --git a/synapse/util/caches/dictionary_cache.py b/synapse/util/caches/dictionary_cache.py
index 588d2d49f2..b3b413b02c 100644
--- a/synapse/util/caches/dictionary_cache.py
+++ b/synapse/util/caches/dictionary_cache.py
@@ -15,26 +15,38 @@
 import enum
 import logging
 import threading
-from collections import namedtuple
-from typing import Any
+from typing import Any, Dict, Generic, Iterable, Optional, Set, TypeVar
+
+import attr
 
 from synapse.util.caches.lrucache import LruCache
 
 logger = logging.getLogger(__name__)
 
 
-class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "known_absent", "value"))):
+# The type of the cache keys.
+KT = TypeVar("KT")
+# The type of the dictionary keys.
+DKT = TypeVar("DKT")
+
+
+@attr.s(slots=True)
+class DictionaryEntry:
     """Returned when getting an entry from the cache
 
     Attributes:
-        full (bool): Whether the cache has the full or dict or just some keys.
+        full: Whether the cache has the full or dict or just some keys.
             If not full then not all requested keys will necessarily be present
             in `value`
-        known_absent (set): Keys that were looked up in the dict and were not
+        known_absent: Keys that were looked up in the dict and were not
             there.
-        value (dict): The full or partial dict value
+        value: The full or partial dict value
     """
 
+    full = attr.ib(type=bool)
+    known_absent = attr.ib()
+    value = attr.ib()
+
     def __len__(self):
         return len(self.value)
 
@@ -45,21 +57,21 @@ class _Sentinel(enum.Enum):
     sentinel = object()
 
 
-class DictionaryCache:
+class DictionaryCache(Generic[KT, DKT]):
     """Caches key -> dictionary lookups, supporting caching partial dicts, i.e.
     fetching a subset of dictionary keys for a particular key.
     """
 
-    def __init__(self, name, max_entries=1000):
+    def __init__(self, name: str, max_entries: int = 1000):
         self.cache = LruCache(
             max_size=max_entries, cache_name=name, size_callback=len
-        )  # type: LruCache[Any, DictionaryEntry]
+        )  # type: LruCache[KT, DictionaryEntry]
 
         self.name = name
         self.sequence = 0
-        self.thread = None
+        self.thread = None  # type: Optional[threading.Thread]
 
-    def check_thread(self):
+    def check_thread(self) -> None:
         expected_thread = self.thread
         if expected_thread is None:
             self.thread = threading.current_thread()
@@ -69,12 +81,14 @@ class DictionaryCache:
                     "Cache objects can only be accessed from the main thread"
                 )
 
-    def get(self, key, dict_keys=None):
+    def get(
+        self, key: KT, dict_keys: Optional[Iterable[DKT]] = None
+    ) -> DictionaryEntry:
         """Fetch an entry out of the cache
 
         Args:
             key
-            dict_key(list): If given a set of keys then return only those keys
+            dict_key: If given a set of keys then return only those keys
                 that exist in the cache.
 
         Returns:
@@ -95,7 +109,7 @@ class DictionaryCache:
 
         return DictionaryEntry(False, set(), {})
 
-    def invalidate(self, key):
+    def invalidate(self, key: KT) -> None:
         self.check_thread()
 
         # Increment the sequence number so that any SELECT statements that
@@ -103,19 +117,25 @@ class DictionaryCache:
         self.sequence += 1
         self.cache.pop(key, None)
 
-    def invalidate_all(self):
+    def invalidate_all(self) -> None:
         self.check_thread()
         self.sequence += 1
         self.cache.clear()
 
-    def update(self, sequence, key, value, fetched_keys=None):
+    def update(
+        self,
+        sequence: int,
+        key: KT,
+        value: Dict[DKT, Any],
+        fetched_keys: Optional[Set[DKT]] = None,
+    ) -> None:
         """Updates the entry in the cache
 
         Args:
             sequence
-            key (K)
-            value (dict[X,Y]): The value to update the cache with.
-            fetched_keys (None|set[X]): All of the dictionary keys which were
+            key
+            value: The value to update the cache with.
+            fetched_keys: All of the dictionary keys which were
                 fetched from the database.
 
                 If None, this is the complete value for key K. Otherwise, it
@@ -131,7 +151,9 @@ class DictionaryCache:
             else:
                 self._update_or_insert(key, value, fetched_keys)
 
-    def _update_or_insert(self, key, value, known_absent):
+    def _update_or_insert(
+        self, key: KT, value: Dict[DKT, Any], known_absent: Set[DKT]
+    ) -> None:
         # We pop and reinsert as we need to tell the cache the size may have
         # changed
 
@@ -140,5 +162,5 @@ class DictionaryCache:
         entry.known_absent.update(known_absent)
         self.cache[key] = entry
 
-    def _insert(self, key, value, known_absent):
+    def _insert(self, key: KT, value: Dict[DKT, Any], known_absent: Set[DKT]) -> None:
         self.cache[key] = DictionaryEntry(True, known_absent, value)
diff --git a/synapse/util/caches/ttlcache.py b/synapse/util/caches/ttlcache.py
index 6ce2a3d12b..96a8274940 100644
--- a/synapse/util/caches/ttlcache.py
+++ b/synapse/util/caches/ttlcache.py
@@ -15,6 +15,7 @@
 
 import logging
 import time
+from typing import Any, Callable, Dict, Generic, Tuple, TypeVar, Union
 
 import attr
 from sortedcontainers import SortedList
@@ -23,15 +24,19 @@ from synapse.util.caches import register_cache
 
 logger = logging.getLogger(__name__)
 
-SENTINEL = object()
+SENTINEL = object()  # type: Any
 
+T = TypeVar("T")
+KT = TypeVar("KT")
+VT = TypeVar("VT")
 
-class TTLCache:
+
+class TTLCache(Generic[KT, VT]):
     """A key/value cache implementation where each entry has its own TTL"""
 
-    def __init__(self, cache_name, timer=time.time):
+    def __init__(self, cache_name: str, timer: Callable[[], float] = time.time):
         # map from key to _CacheEntry
-        self._data = {}
+        self._data = {}  # type: Dict[KT, _CacheEntry]
 
         # the _CacheEntries, sorted by expiry time
         self._expiry_list = SortedList()  # type: SortedList[_CacheEntry]
@@ -40,26 +45,27 @@ class TTLCache:
 
         self._metrics = register_cache("ttl", cache_name, self, resizable=False)
 
-    def set(self, key, value, ttl):
+    def set(self, key: KT, value: VT, ttl: float) -> None:
         """Add/update an entry in the cache
 
         Args:
             key: key for this entry
             value: value for this entry
-            ttl (float): TTL for this entry, in seconds
+            ttl: TTL for this entry, in seconds
         """
         expiry = self._timer() + ttl
 
         self.expire()
         e = self._data.pop(key, SENTINEL)
-        if e != SENTINEL:
+        if e is not SENTINEL:
+            assert isinstance(e, _CacheEntry)
             self._expiry_list.remove(e)
 
         entry = _CacheEntry(expiry_time=expiry, ttl=ttl, key=key, value=value)
         self._data[key] = entry
         self._expiry_list.add(entry)
 
-    def get(self, key, default=SENTINEL):
+    def get(self, key: KT, default: T = SENTINEL) -> Union[VT, T]:
         """Get a value from the cache
 
         Args:
@@ -72,23 +78,23 @@ class TTLCache:
         """
         self.expire()
         e = self._data.get(key, SENTINEL)
-        if e == SENTINEL:
+        if e is SENTINEL:
             self._metrics.inc_misses()
-            if default == SENTINEL:
+            if default is SENTINEL:
                 raise KeyError(key)
             return default
+        assert isinstance(e, _CacheEntry)
         self._metrics.inc_hits()
         return e.value
 
-    def get_with_expiry(self, key):
+    def get_with_expiry(self, key: KT) -> Tuple[VT, float, float]:
         """Get a value, and its expiry time, from the cache
 
         Args:
             key: key to look up
 
         Returns:
-            Tuple[Any, float, float]: the value from the cache, the expiry time
-            and the TTL
+            A tuple of  the value from the cache, the expiry time and the TTL
 
         Raises:
             KeyError if the entry is not found
@@ -102,7 +108,7 @@ class TTLCache:
         self._metrics.inc_hits()
         return e.value, e.expiry_time, e.ttl
 
-    def pop(self, key, default=SENTINEL):
+    def pop(self, key: KT, default: T = SENTINEL) -> Union[VT, T]:  # type: ignore
         """Remove a value from the cache
 
         If key is in the cache, remove it and return its value, else return default.
@@ -118,29 +124,30 @@ class TTLCache:
         """
         self.expire()
         e = self._data.pop(key, SENTINEL)
-        if e == SENTINEL:
+        if e is SENTINEL:
             self._metrics.inc_misses()
-            if default == SENTINEL:
+            if default is SENTINEL:
                 raise KeyError(key)
             return default
+        assert isinstance(e, _CacheEntry)
         self._expiry_list.remove(e)
         self._metrics.inc_hits()
         return e.value
 
-    def __getitem__(self, key):
+    def __getitem__(self, key: KT) -> VT:
         return self.get(key)
 
-    def __delitem__(self, key):
+    def __delitem__(self, key: KT) -> None:
         self.pop(key)
 
-    def __contains__(self, key):
+    def __contains__(self, key: KT) -> bool:
         return key in self._data
 
-    def __len__(self):
+    def __len__(self) -> int:
         self.expire()
         return len(self._data)
 
-    def expire(self):
+    def expire(self) -> None:
         """Run the expiry on the cache. Any entries whose expiry times are due will
         be removed
         """
@@ -158,7 +165,7 @@ class _CacheEntry:
     """TTLCache entry"""
 
     # expiry_time is the first attribute, so that entries are sorted by expiry.
-    expiry_time = attr.ib()
-    ttl = attr.ib()
+    expiry_time = attr.ib(type=float)
+    ttl = attr.ib(type=float)
     key = attr.ib()
     value = attr.ib()