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.

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

@@ -14,6 +14,7 @@
 # END HEADER
 
 from contextlib import contextmanager
+import threading
 
 from hypothesis.errors import InvalidArgument
 from hypothesis.internal.lazyformat import lazyformat
@@ -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.data = threading.local()
+
+    @property
+    def marker(self):
+        return getattr(self.data, "marker", 0)
+
+    @marker.setter
+    def marker(self, value):
+        self.data.marker = value
+
+    @property
+    def currently_capped(self):
+        return getattr(self.data, "currently_capped", False)
+
+    @currently_capped.setter
+    def currently_capped(self, value):
+        self.data.currently_capped = value
 
     def __repr__(self):
         return "LimitedStrategy(%r)" % (self.base_strategy,)

hypothesis-python/tests/cover/test_recursive.py

@@ -12,6 +12,7 @@
 # obtain one at https://mozilla.org/MPL/2.0/.
 #
 # END HEADER
+import threading
 
 import pytest
 
@@ -77,3 +78,32 @@ def test_can_exclude_branching_with_max_leaves(t):
 @given(st.recursive(st.none(), lambda x: st.one_of(x, x)))
 def test_issue_1502_regression(s):
     pass
+
+
+def test_thread_save_draw():
+    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(2):
+        threads.append(threading.Thread(target=test))
+
+    for thread in threads:
+        thread.start()
+
+    for thread in threads:
+        thread.join()
+
+    assert not errors