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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Crash on Event invocation with ref parameter","articleBody":"### Environment\r\n\r\n-   Pythonnet version: 2.5.1\r\n-   Python version: 3.6.5\r\n-   Operating System: Windows 10\r\n-   .NET Runtime: 4.8.4250.0\r\n\r\n### Details\r\n\r\n-   When I try to invoke a .NET event that takes a `ref` parameter, the python process crashes. I provided the code to reproduce the issue below.\r\n\r\n***Note:*** I cannot change the code to not use `ref` as the `ref` delegate is coming from a 3rd party library. I can wrap around it with a lightweight C# piece of code but would rather avoid it if possible.\r\n***Note:*** This may be related to the following issue: https://github.com/pythonnet/pythonnet/issues/965\r\n\r\n#### Windows Event Viewer Error 1: Source - .NET Runtime\r\n```\r\nApplication: python.exe\r\nFramework Version: v4.0.30319\r\nDescription: The process was terminated due to an internal error in the .NET Runtime at IP 00007FF81CEA3D2E (00007FF81CEA0000) with exit code 80131506.\r\n```\r\n\r\n#### Windows Event Viewer Error 2: Source - Application Error\r\n```\r\nFaulting application name: python.exe, version: 3.6.5150.1013, time stamp: 0x5abbcb08\r\nFaulting module name: clr.dll, version: 4.8.4250.0, time stamp: 0x5f2a059c\r\nException code: 0xc0000005\r\nFault offset: 0x0000000000003d2e\r\nFaulting process id: 0x4348\r\nFaulting application start time: 0x01d6eaa4a034a863\r\nFaulting application path: C:\\Users\\noam.bonnie\\dev\\hp-bluetooth-service\\.tox\\py36\\Scripts\\python.exe\r\nFaulting module path: C:\\Windows\\Microsoft.NET\\Framework64\\v4.0.30319\\clr.dll\r\nReport Id: c2031029-3b2f-4e61-aa84-5e5502e904d2\r\nFaulting package full name: \r\nFaulting package-relative application ID: \r\n```\r\n\r\n#### The C# class with `ref` parameter for the delegate. Removing the `ref` resolves the problem\r\n```C#\r\nusing System;\r\n\r\nnamespace TestEvent\r\n{\r\n    public delegate void MyEvent(ref string data); \r\n\r\n    public class MyTest\r\n    {\r\n        public event MyEvent myEvent;\r\n\r\n        public virtual void triggerEvent()\r\n        {\r\n            Console.WriteLine(\"Invoking Event!\");\r\n            string myStr = \"This is the event data\";\r\n            myEvent?.Invoke(ref myStr);\r\n        }\r\n    }\r\n}    \r\n```\r\n#### Python program to invoke the event. Crashes. \r\n```python\r\nimport clr\r\nimport os\r\nimport sys\r\n\r\n\r\ndef handleEventData(data):\r\n    print(\"=== event invoked. data: {} ===\".format(data))\r\n\r\n\r\ntry:\r\n    # load the library of the C# class above from a 'lib' local directory. \r\n    # not necessary if the library of the C# dll is in the path\r\n    lib_path = os.path.join(os.path.dirname(os.path.abspath(__file__)), 'lib')\r\n    sys.path.append(lib_path)\r\n    clr.AddReference(\"TestEvent\")\r\n    clr.AddReference(\"System\")\r\n\r\n    # Print the .NET version\r\n    import System\r\n    print(System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription)\r\n\r\n    # Create object, subscribe to event and trigger the event\r\n    import TestEvent\r\n    t = TestEvent.MyTest()\r\n    t.myEvent += handleEventData\r\n    t.triggerEvent()\r\nexcept Exception as e:\r\n    print(e)\r\n```\r\n","author":{"url":"https://github.com/noambonnieclear","@type":"Person","name":"noambonnieclear"},"datePublished":"2021-01-14T21:34:04.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/1355/pythonnet/issues/1355"}