Reduce number of lock/unlock operations in case of cache miss.

Author: Thomas Kemmer

src/cachetools/_decorators.py

@@ -7,21 +7,20 @@ def _cached_locked_info(func, cache, key, lock, info):
     def wrapper(*args, **kwargs):
         nonlocal hits, misses
         k = key(*args, **kwargs)
-        try:
-            with lock:
+        with lock:
+            try:
                 result = cache[k]
                 hits += 1
                 return result
-        except KeyError:
-            with lock:
+            except KeyError:
                 misses += 1
         v = func(*args, **kwargs)
-        # in case of a race, prefer the item already in the cache
-        try:
-            with lock:
+        with lock:
+            try:
+                # in case of a race, prefer the item already in the cache
                 return cache.setdefault(k, v)
-        except ValueError:
-            return v  # value too large
+            except ValueError:
+                return v  # value too large
 
     def cache_clear():
         nonlocal hits, misses
@@ -87,18 +86,18 @@ def cache_clear():
 def _cached_locked(func, cache, key, lock):
     def wrapper(*args, **kwargs):
         k = key(*args, **kwargs)
-        try:
-            with lock:
+        with lock:
+            try:
                 return cache[k]
-        except KeyError:
-            pass  # key not found
+            except KeyError:
+                pass  # key not found
         v = func(*args, **kwargs)
-        # in case of a race, prefer the item already in the cache
-        try:
-            with lock:
+        with lock:
+            try:
+                # in case of a race, prefer the item already in the cache
                 return cache.setdefault(k, v)
-        except ValueError:
-            return v  # value too large
+            except ValueError:
+                return v  # value too large
 
     def cache_clear():
         with lock:

tests/test_cached.py

@@ -165,32 +165,28 @@ def test_decorator_info(self):
         self.assertEqual(wrapper.cache_info(), (0, 0, 2, 0))
 
     def test_decorator_lock_info(self):
-        # hit: lock.count += 1
-        # miss: lock.count += 3 (get, update missed, set)
-        # info: lock.count += 1
-        # clear: lock.count += 1
         cache = self.cache(2)
         lock = CountedLock()
         wrapper = cachetools.cached(cache, lock=lock, info=True)(self.func)
         self.assertEqual(wrapper.cache_info(), (0, 0, 2, 0))
         self.assertEqual(lock.count, 1)
         self.assertEqual(wrapper(0), 0)
-        self.assertEqual(lock.count, 4)
+        self.assertEqual(lock.count, 3)
         self.assertEqual(wrapper.cache_info(), (0, 1, 2, 1))
-        self.assertEqual(lock.count, 5)
+        self.assertEqual(lock.count, 4)
         self.assertEqual(wrapper(1), 1)
-        self.assertEqual(lock.count, 8)
+        self.assertEqual(lock.count, 6)
         self.assertEqual(wrapper.cache_info(), (0, 2, 2, 2))
-        self.assertEqual(lock.count, 9)
+        self.assertEqual(lock.count, 7)
         self.assertEqual(wrapper(0), 0)
-        self.assertEqual(lock.count, 10)
+        self.assertEqual(lock.count, 8)
         self.assertEqual(wrapper.cache_info(), (1, 2, 2, 2))
-        self.assertEqual(lock.count, 11)
+        self.assertEqual(lock.count, 9)
         wrapper.cache_clear()
-        self.assertEqual(lock.count, 12)
+        self.assertEqual(lock.count, 10)
         self.assertEqual(len(cache), 0)
         self.assertEqual(wrapper.cache_info(), (0, 0, 2, 0))
-        self.assertEqual(lock.count, 13)
+        self.assertEqual(lock.count, 11)
 
     def test_zero_size_cache_decorator(self):
         cache = self.cache(0)