Fix libevwrapper atexit cleanup bug causing Python shutdown crashes

cassandra/io/libevreactor.py

@@ -13,7 +13,6 @@
 # limitations under the License.
 import atexit
 from collections import deque
-from functools import partial
 import logging
 import os
 import socket
@@ -227,8 +226,20 @@ def _loop_will_run(self, prepare):
             self._notifier.send()
 
 
+def _atexit_cleanup():
+    """Cleanup function called by atexit that uses the current _global_loop value.
+
+    This wrapper ensures that cleanup receives the actual LibevLoop instance
+    instead of None, which was the value of _global_loop when the module was
+    imported.
+    """
+    global _global_loop
+    if _global_loop is not None:
+        _cleanup(_global_loop)
+
+
 _global_loop = None
-atexit.register(partial(_cleanup, _global_loop))
+atexit.register(_atexit_cleanup)
 
 
 class LibevConnection(Connection):

tests/unit/io/test_libevreactor_shutdown.py

@@ -0,0 +1,236 @@
+# Copyright ScyllaDB, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Test to demonstrate the libevwrapper atexit cleanup issue.
+
+This test demonstrates the problem where the atexit callback is registered
+with _global_loop=None at import time, causing it to receive None during
+shutdown instead of the actual loop instance.
+"""
+
+import unittest
+import sys
+import subprocess
+import tempfile
+import os
+from pathlib import Path
+
+from cassandra import DependencyException
+
+try:
+    from cassandra.io.libevreactor import LibevConnection
+except (ImportError, DependencyException):
+    LibevConnection = None
+
+from tests import is_monkey_patched
+
+
+class LibevAtexitCleanupTest(unittest.TestCase):
+    """
+    Test case to demonstrate the atexit cleanup bug in libevreactor.
+
+    The bug: atexit.register(partial(_cleanup, _global_loop)) is called when
+    _global_loop is None, so the cleanup function receives None at shutdown
+    instead of the actual LibevLoop instance that was created later.
+    """
+
+    def setUp(self):
+        if is_monkey_patched():
+            raise unittest.SkipTest("Can't test libev with monkey patching")
+        if LibevConnection is None:
+            raise unittest.SkipTest('libev does not appear to be installed correctly')
+
+    def test_atexit_callback_uses_current_global_loop(self):
+        """
+        Test that verifies the atexit callback fix.
+
+        The fix uses a wrapper function _atexit_cleanup() that looks up the
+        current value of _global_loop at shutdown time, instead of capturing
+        it at import time with partial().
+
+        @since 3.29
+        @jira_ticket PYTHON-XXX
+        @expected_result The atexit handler calls cleanup with the actual loop
+
+        @test_category connection
+        """
+        from cassandra.io import libevreactor
+
+        # Verify the fix: _atexit_cleanup should exist as a module-level function
+        self.assertTrue(hasattr(libevreactor, '_atexit_cleanup'),
+                       "Module should have _atexit_cleanup function")
+
+        # Verify it's not a partial (the old buggy implementation)
+        from functools import partial
+        self.assertNotIsInstance(libevreactor._atexit_cleanup, partial,
+                                "The _atexit_cleanup should NOT be a partial function")
+
+        # Verify it's actually a function
+        self.assertTrue(callable(libevreactor._atexit_cleanup),
+                       "_atexit_cleanup should be callable")
+
+        # Initialize the reactor
+        LibevConnection.initialize_reactor()
+
+        # At this point, libevreactor._global_loop is not None
+        self.assertIsNotNone(libevreactor._global_loop,
+                           "Global loop should be initialized")
+
+        # The fix: _atexit_cleanup is a function that will look up
+        # _global_loop when it's called, not a partial with captured args
+        self.assertEqual(libevreactor._atexit_cleanup.__name__, '_atexit_cleanup',
+                        "The function should have the correct name")
+
+    def test_shutdown_cleanup_works_with_fix(self):
+        """
+        Test that verifies the atexit cleanup fix works in a subprocess.
+
+        This test creates a minimal script that:
+        1. Imports the driver
+        2. Initializes the reactor (creates the global loop)
+        3. Verifies the _atexit_cleanup function is available
+        4. Exits without explicit cleanup
+
+        With the fix, atexit should properly clean up the loop using the
+        wrapper function that looks up _global_loop at shutdown time.
+
+        @since 3.29
+        @jira_ticket PYTHON-XXX
+        @expected_result The subprocess shows the fix is working
+
+        @test_category connection
+        """
+        # Create a test script that verifies the fix
+        test_script = '''
+import sys
+import os
+
+# Add the driver path
+sys.path.insert(0, {driver_path!r})
+
+# Import and setup
+from cassandra.io import libevreactor
+from cassandra.io.libevreactor import LibevConnection
+import atexit
+
+# Initialize the reactor (creates the global loop)
+LibevConnection.initialize_reactor()
+
+print("Global loop initialized:", libevreactor._global_loop is not None)
+
+# Verify the fix is in place: _atexit_cleanup should be a module-level function
+if hasattr(libevreactor, '_atexit_cleanup'):
+    print("FIXED: Module has _atexit_cleanup function")
+    print("This function will look up _global_loop at shutdown time")
+    # Verify it's not using partial with None
+    import inspect
+    source = inspect.getsource(libevreactor._atexit_cleanup)
+    if "global _global_loop" in source and "_global_loop is not None" in source:
+        print("Verified: _atexit_cleanup uses current _global_loop value")
+else:
+    print("BUG: No _atexit_cleanup function found")
+
+# Exit without explicit cleanup - atexit should handle it properly with the fix!
+print("Exiting with proper cleanup...")
+'''
+
+        driver_path = str(Path(__file__).parent.parent.parent.parent)
+        script_content = test_script.format(driver_path=driver_path)
+
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.py', delete=False) as f:
+            f.write(script_content)
+            script_path = f.name
+
+        try:
+            result = subprocess.run(
+                [sys.executable, script_path],
+                capture_output=True,
+                text=True,
+                timeout=5
+            )
+
+            output = result.stdout
+            print("\n=== Subprocess Output ===")
+            print(output)
+            print("=== End Output ===\n")
+
+            # Verify the output shows the fix is working
+            self.assertIn("Global loop initialized: True", output)
+            self.assertIn("FIXED: Module has _atexit_cleanup function", output)
+            self.assertIn("Verified: _atexit_cleanup uses current _global_loop value", output)
+            self.assertNotIn("BUG", output.replace("BUG STILL PRESENT", "").replace("DEBUG", ""))  # Allow "BUG" only in success message
+
+        finally:
+            os.unlink(script_path)
+
+
+class LibevShutdownRaceConditionTest(unittest.TestCase):
+    """
+    Tests to analyze potential race conditions and crashes during shutdown.
+    """
+
+    def setUp(self):
+        if is_monkey_patched():
+            raise unittest.SkipTest("Can't test libev with monkey patching")
+        if LibevConnection is None:
+            raise unittest.SkipTest('libev does not appear to be installed correctly')
+
+    def test_cleanup_with_fix_properly_shuts_down(self):
+        """
+        Test to verify the fix properly shuts down the event loop.
+
+        With the fix in place, the atexit cleanup will:
+        1. Look up the current _global_loop value (not None)
+        2. Call _cleanup with the actual loop instance
+        3. Properly shut down the loop and its watchers
+
+        This prevents the crash scenario where:
+        - Various modules are being torn down during Python shutdown
+        - The libev event loop is still running
+        - Callbacks fire and try to access deallocated Python objects
+
+        @since 3.29
+        @jira_ticket PYTHON-XXX
+        @expected_result Cleanup properly shuts down the loop with the fix
+
+        @test_category connection
+        """
+        from cassandra.io import libevreactor
+        from cassandra.io.libevreactor import _cleanup, _atexit_cleanup
+
+        LibevConnection.initialize_reactor()
+
+        # Verify the loop exists
+        self.assertIsNotNone(libevreactor._global_loop)
+
+        # Before cleanup, the loop should not be shut down
+        self.assertFalse(libevreactor._global_loop._shutdown,
+                        "Loop should not be shut down initially")
+
+        # Simulate what the OLD buggy code would do
+        _cleanup(None)  # This does nothing
+        self.assertFalse(libevreactor._global_loop._shutdown,
+                        "Loop should NOT be shut down when cleanup receives None")
+
+        # Now test the FIX: call the wrapper that looks up _global_loop
+        _atexit_cleanup()  # This is what atexit will actually call
+
+        # With the fix, the loop should be properly shut down
+        self.assertTrue(libevreactor._global_loop._shutdown,
+                       "Loop should be shut down when _atexit_cleanup is called")
+
+
+if __name__ == '__main__':
+    unittest.main()