Releasing GIL in long-running C# method causes "Fatal Python error: PyEval_SaveThread: the function must be called with the GIL held, but the GIL is released (the current Python thread state is NULL)" #2209

sherryyshi · 2023-08-04T21:41:31Z

sherryyshi
Aug 4, 2023

Environment

Pythonnet version: 3.0.1
Python version: 3.9.13
Operating System: Windows 11
.NET Runtime: .NET Core 3.1

Details

I'm trying to prevent a long running method in C# from blocking execution in Python. I followed the guidance on https://github.com/pythonnet/pythonnet/wiki/Threading but I am getting a crash.

What commands did you run to trigger this issue? If you can provide a
Minimal, Complete, and Verifiable example
this will help us understand the issue.

import pythonnet
pythonnet.load('coreclr')

import os
bin_path = os.path.normpath(os.path.dirname(os.path.abspath(__file__)) + "/../LongRunningTask/bin/Debug/netcoreapp3.1")

import clr
clr.AddReference(os.path.join(bin_path, "LongRunningTask"))
clr.AddReference("System")

from LongRunningTask import LongRunningTask
from threading import Thread, Timer

t1 = Thread(target=LongRunningTask.Run)

t1.daemon = True
t1.start()

using System.Threading;
using Python.Runtime;

namespace LongRunningTask
{
    public class LongRunningTask
    {
        public static void Run()
        {
            var state = PythonEngine.BeginAllowThreads();
            Thread.Sleep(1000);
            PythonEngine.EndAllowThreads(state);
        }
    }
}

If there was a crash, please include the traceback here.

Fatal Python error: PyGILState_Release: thread state 000001D4A5CA2A40 must be current when releasing
Python runtime state: initialized

Thread 0x00001c08 (most recent call first):
  File "C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python39_64\lib\threading.py", line 917 in run
  File "C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python39_64\lib\threading.py", line 980 in _bootstrap_inner
  File "C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python39_64\lib\threading.py", line 937 in _bootstrap

Current thread 0x00005f6c (most recent call first):
  File "C:\Users\shersh\AppData\Roaming\Python\Python39\site-packages\clr_loader\types.py", line 64 in __call__
  File "C:\Users\shersh\AppData\Roaming\Python\Python39\site-packages\pythonnet\__init__.py", line 157 in unload
Fatal error. System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at Python.Runtime.Runtime.PyGILState_Release(Python.Runtime.Native.PyGILState)
   at Python.Runtime.PythonEngine.ReleaseLock(Python.Runtime.Native.PyGILState)
   at Python.Runtime.Py+GILState.Dispose()
   at Python.Runtime.Loader.Shutdown(IntPtr, Int32)

lostmsu · 2023-08-04T22:07:11Z

lostmsu
Aug 4, 2023
Maintainer

When Python calls C# GIL is not held in the first place, so no need to release anything.

1 reply

sherryyshi Aug 4, 2023
Author

I see, thanks.

DareDevilDenis · 2024-11-13T16:17:52Z

DareDevilDenis
Nov 13, 2024

Hi @lostmsu. I'm confused by your comment:

"When Python calls C# GIL is not held in the first place, so no need to release anything"

This seems to contradict this page https://github.com/pythonnet/pythonnet/wiki/Threading which says:

"If you are calling C# from Python, and the C# code performs a long-running operation (e.g. computation, I/O, sleep, acquiring a lock, ...), release the GIL via PythonEngine.BeginAllowThreads(). Remember to restore it before returning control to Python"

The same question is here: #2424

2 replies

lostmsu Nov 14, 2024
Maintainer

This might be confusing. I believe by default now GIL is not held when .NET code is called from Python. So actually in order to work with any Python objects you have to call and hold Py.GIL().

The wiki is outdated.

DareDevilDenis Nov 14, 2024

Thanks for the clarification

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Releasing GIL in long-running C# method causes "Fatal Python error: PyEval_SaveThread: the function must be called with the GIL held, but the GIL is released (the current Python thread state is NULL)" #2209

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sherryyshi Aug 4, 2023

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sherryyshi
Aug 4, 2023

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lostmsu
Aug 4, 2023
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sherryyshi Aug 4, 2023
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DareDevilDenis
Nov 13, 2024

lostmsu Nov 14, 2024
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