Merge pull request #4455 from tybug/free-threading-global-random-lock

Add a lock to `deterministic_PRNG`

Author: Liam-DeVoe

hypothesis-python/RELEASE.rst

@@ -0,0 +1,3 @@
+RELEASE_TYPE: patch
+
+Improve threading compatibility of an internal helper for managing deterministic rng seeding.

hypothesis-python/src/hypothesis/core.py

@@ -140,6 +140,7 @@
     SearchStrategy,
     check_strategy,
 )
+from hypothesis.utils.threading import ThreadLocal
 from hypothesis.vendor.pretty import RepresentationPrinter
 from hypothesis.version import __version__
 
@@ -149,7 +150,11 @@
 running_under_pytest = False
 pytest_shows_exceptiongroups = True
 global_force_seed = None
-_hypothesis_global_random = None
+# `threadlocal` stores "engine-global" constants, which are global relative to a
+# ConjectureRunner instance (roughly speaking). Since only one conjecture runner
+# instance can be active per thread, making engine constants thread-local prevents
+# the ConjectureRunner instances of concurrent threads from treading on each other.
+threadlocal = ThreadLocal(_hypothesis_global_random=None)
 
 
 @dataclass
@@ -703,10 +708,9 @@ def get_random_for_wrapped_test(test, wrapped_test):
     elif global_force_seed is not None:
         return Random(global_force_seed)
     else:
-        global _hypothesis_global_random
-        if _hypothesis_global_random is None:  # pragma: no cover
-            _hypothesis_global_random = Random()
-        seed = _hypothesis_global_random.getrandbits(128)
+        if threadlocal._hypothesis_global_random is None:  # pragma: no cover
+            threadlocal._hypothesis_global_random = Random()
+        seed = threadlocal._hypothesis_global_random.getrandbits(128)
         wrapped_test._hypothesis_internal_use_generated_seed = seed
         return Random(seed)
 

hypothesis-python/src/hypothesis/internal/entropy.py

@@ -195,9 +195,11 @@ def deterministic_PRNG(seed: int = 0) -> Generator[None, None, None]:
     bad idea in principle, and breaks all kinds of independence assumptions
     in practice.
     """
-    if hypothesis.core._hypothesis_global_random is None:  # pragma: no cover
-        hypothesis.core._hypothesis_global_random = random.Random()
-        register_random(hypothesis.core._hypothesis_global_random)
+    if (
+        hypothesis.core.threadlocal._hypothesis_global_random is None
+    ):  # pragma: no cover
+        hypothesis.core.threadlocal._hypothesis_global_random = random.Random()
+        register_random(hypothesis.core.threadlocal._hypothesis_global_random)
 
     seed_all, restore_all = get_seeder_and_restorer(seed)
     seed_all()

hypothesis-python/src/hypothesis/utils/threading.py

@@ -0,0 +1,44 @@
+# This file is part of Hypothesis, which may be found at
+# https://github.com/HypothesisWorks/hypothesis/
+#
+# Copyright the Hypothesis Authors.
+# Individual contributors are listed in AUTHORS.rst and the git log.
+#
+# This Source Code Form is subject to the terms of the Mozilla Public License,
+# v. 2.0. If a copy of the MPL was not distributed with this file, You can
+# obtain one at https://mozilla.org/MPL/2.0/.
+
+import threading
+from typing import Any
+
+
+class ThreadLocal:
+    """
+    Manages thread-local state. ThreadLocal forwards getattr and setattr to a
+    threading.local() instance. The passed kwargs defines the available attributes
+    on the threadlocal and their default values.
+
+    The only supported names to geattr and setattr are the keys of the passed kwargs.
+    """
+
+    def __init__(self, **kwargs: Any) -> None:
+        self.__initialized = False
+        self.__kwargs = kwargs
+        self.__threadlocal = threading.local()
+        self.__initialized = True
+
+    def __getattr__(self, name: str) -> Any:
+        if name not in self.__kwargs:
+            raise AttributeError(f"No attribute {name}")
+        if not hasattr(self.__threadlocal, name):
+            setattr(self.__threadlocal, name, self.__kwargs[name])
+        return getattr(self.__threadlocal, name)
+
+    def __setattr__(self, name: str, value: Any) -> None:
+        # disable attribute-forwarding while initializing
+        if "_ThreadLocal__initialized" not in self.__dict__ or not self.__initialized:
+            super().__setattr__(name, value)
+        else:
+            if name not in self.__kwargs:
+                raise AttributeError(f"No attribute {name}")
+            setattr(self.__threadlocal, name, value)

hypothesis-python/tests/cover/test_random_module.py

@@ -133,11 +133,11 @@ def test(r):
 
         test()
         state_a = random.getstate()
-        state_a2 = core._hypothesis_global_random.getstate()
+        state_a2 = core.threadlocal._hypothesis_global_random.getstate()
 
         test()
         state_b = random.getstate()
-        state_b2 = core._hypothesis_global_random.getstate()
+        state_b2 = core.threadlocal._hypothesis_global_random.getstate()
 
         assert state_a == state_b
         assert state_a2 != state_b2
@@ -147,11 +147,11 @@ def test_find_does_not_pollute_state():
     with deterministic_PRNG():
         find(st.random_module(), lambda r: True)
         state_a = random.getstate()
-        state_a2 = core._hypothesis_global_random.getstate()
+        state_a2 = core.threadlocal._hypothesis_global_random.getstate()
 
         find(st.random_module(), lambda r: True)
         state_b = random.getstate()
-        state_b2 = core._hypothesis_global_random.getstate()
+        state_b2 = core.threadlocal._hypothesis_global_random.getstate()
 
         assert state_a == state_b
         assert state_a2 != state_b2

hypothesis-python/tests/cover/test_threading.py

@@ -0,0 +1,47 @@
+# This file is part of Hypothesis, which may be found at
+# https://github.com/HypothesisWorks/hypothesis/
+#
+# Copyright the Hypothesis Authors.
+# Individual contributors are listed in AUTHORS.rst and the git log.
+#
+# This Source Code Form is subject to the terms of the Mozilla Public License,
+# v. 2.0. If a copy of the MPL was not distributed with this file, You can
+# obtain one at https://mozilla.org/MPL/2.0/.
+
+import pytest
+
+from hypothesis.utils.threading import ThreadLocal
+
+
+def test_threadlocal_setattr_and_getattr():
+    threadlocal = ThreadLocal(a=1, b=2)
+    assert threadlocal.a == 1
+    assert threadlocal.b == 2
+    # check that we didn't add attributes to the ThreadLocal instance itself
+    # instead of its threading.local() variable
+    assert set(threadlocal.__dict__) == {
+        "_ThreadLocal__initialized",
+        "_ThreadLocal__kwargs",
+        "_ThreadLocal__threadlocal",
+    }
+
+    threadlocal.a = 3
+    assert threadlocal.a == 3
+    assert threadlocal.b == 2
+    assert set(threadlocal.__dict__) == {
+        "_ThreadLocal__initialized",
+        "_ThreadLocal__kwargs",
+        "_ThreadLocal__threadlocal",
+    }
+
+
+def test_nonexistent_getattr_raises():
+    threadlocal = ThreadLocal(a=1)
+    with pytest.raises(AttributeError):
+        _c = threadlocal.c
+
+
+def test_nonexistent_setattr_raises():
+    threadlocal = ThreadLocal(a=1)
+    with pytest.raises(AttributeError):
+        threadlocal.c = 2

hypothesis-python/tests/nocover/test_randomization.py

@@ -40,11 +40,11 @@ def f1(n):
     def f2(n):
         choices2.append(n)
 
-    core._hypothesis_global_random = Random(0)
-    state = core._hypothesis_global_random.getstate()
+    core.threadlocal._hypothesis_global_random = Random(0)
+    state = core.threadlocal._hypothesis_global_random.getstate()
     f1()
 
-    core._hypothesis_global_random.setstate(state)
+    core.threadlocal._hypothesis_global_random.setstate(state)
     f2()
 
     assert choices1 == choices2