Merge pull request #3203 from Zac-HD/lru-keyerror

Zac-HD · web-flow · commit a214abdcfb02 · 2021-12-31T13:07:07.000+11:00
Fix LR-reused cache bug
diff --git a/hypothesis-python/RELEASE.rst b/hypothesis-python/RELEASE.rst
@@ -0,0 +1,5 @@
+RELEASE_TYPE: patch
+
+This patch fixes :issue:`3169`, an extremely rare bug which would
+trigger if an internal least-recently-reused cache dropped a newly
+added entry immediately after it was added.
diff --git a/hypothesis-python/src/hypothesis/internal/cache.py b/hypothesis-python/src/hypothesis/internal/cache.py
@@ -262,3 +262,16 @@ def on_access(self, key, value, score):
         score[0] = 2
         score[1] = self.tick()
         return score
+
+    def pin(self, key):
+        try:
+            super().pin(key)
+        except KeyError:
+            # The whole point of an LRU cache is that it might drop things for you
+            assert key not in self.keys_to_indices
+
+    def unpin(self, key):
+        try:
+            super().unpin(key)
+        except KeyError:
+            assert key not in self.keys_to_indices
diff --git a/hypothesis-python/tests/cover/test_cache_implementation.py b/hypothesis-python/tests/cover/test_cache_implementation.py
@@ -316,3 +316,19 @@ def target():
         worker.join()
 
     assert not errors
+
+
+def test_pin_and_unpin_are_noops_if_dropped():
+    # See https://github.com/HypothesisWorks/hypothesis/issues/3169
+    cache = LRUReusedCache(max_size=10)
+    cache[30] = True
+    assert 30 in cache
+
+    for i in range(20):
+        cache[i] = False
+
+    assert 30 not in cache
+    cache.pin(30)
+    assert 30 not in cache
+    cache.unpin(30)
+    assert 30 not in cache
