Fix race condition inside recursive strategies

hypothesis-python/RELEASE.rst

@@ -0,0 +1,5 @@
+RELEASE_TYPE: patch
+
+This release prevents a race condition inside :func:`~hypothesis.strategies.recursive` strategies.
+The race condition occurs when the same :func:`~hypothesis.strategies.recursive` strategy is shared among tests
+that are running in multiple threads (:issue:`2717`).

hypothesis-python/src/hypothesis/strategies/_internal/recursive.py

@@ -13,6 +13,7 @@
 #
 # END HEADER
 
+import threading
 from contextlib import contextmanager
 
 from hypothesis.errors import InvalidArgument
@@ -29,8 +30,23 @@ class LimitedStrategy(SearchStrategy):
     def __init__(self, strategy):
         super().__init__()
         self.base_strategy = strategy
-        self.marker = 0
-        self.currently_capped = False
+        self._threadlocal = threading.local()
+
+    @property
+    def marker(self):
+        return getattr(self._threadlocal, "marker", 0)
+
+    @marker.setter
+    def marker(self, value):
+        self._threadlocal.marker = value
+
+    @property
+    def currently_capped(self):
+        return getattr(self._threadlocal, "currently_capped", False)
+
+    @currently_capped.setter
+    def currently_capped(self, value):
+        self._threadlocal.currently_capped = value
 
     def __repr__(self):
         return "LimitedStrategy(%r)" % (self.base_strategy,)

hypothesis-python/tests/nocover/test_recursive.py

@@ -13,7 +13,9 @@
 #
 # END HEADER
 
-from hypothesis import settings, strategies as st
+import threading
+
+from hypothesis import given, settings, strategies as st
 from tests.common.debug import find_any, minimal
 from tests.common.utils import flaky
 
@@ -127,3 +129,29 @@ def test_can_form_sets_of_recursive_data():
     )
     xs = minimal(trees, lambda x: len(x) >= size, timeout_after=None)
     assert len(xs) == size
+
+
+def test_drawing_from_recursive_strategy_is_thread_safe():
+    shared_strategy = st.recursive(st.integers(), lambda s: st.lists(s, max_size=3))
+
+    errors = []
+
+    @given(data=st.data())
+    def test(data):
+        try:
+            data.draw(shared_strategy)
+        except Exception as exc:
+            errors.append(exc)
+
+    threads = []
+
+    for _ in range(4):
+        threads.append(threading.Thread(target=test))
+
+    for thread in threads:
+        thread.start()
+
+    for thread in threads:
+        thread.join()
+
+    assert not errors