Environment

• Pythonnet version: 2.5.2
• Python version: issue verified on 3.7.2, 3.7.7 and 3.8.6
• Operating System: Windows 10 64bit
• .NET Runtime: .NET Framework 4.7.2

Details

Hello everybody and thanks for this great piece of Software!

The basic issue is:

• if I throw a .NET exception from within C# code
• and the exception moves into the python space
  • i.e. the C# method was called from python
• then the memory of the exception does not get released anymore

This becomes apparent when you throw quite a lot of exceptions and your applications runs 24/7.

Reproducability

The issue is fairly easy to reproduce. I have also setup a sample repository, which reproduces the issue.

https://github.com/Rookfighter/pythonnet-memleak-exceptions

The basis instruction are:

• setup a Visual Studio Project of the type "Class Library .NET Framework 4.7.2"
• create a ExceptionThrower class

using System;

namespace LeakingExceptions
{
    public class ExceptionThrower
    {
        public void ThrowException()
        {
            throw new Exception("a simple exception");
        }
    }
}

• create a python script which imports the assembly
• create a ExceptionThrower object and call ThrowException within a looped try except block

import os
import __main__

import clr

# bin dir must be adjusted to your relative path!
bin_dir = os.path.abspath(os.path.join(os.path.dirname(__main__.__file__), '../Source/LeakingExceptions/bin/Debug'))
clr.AddReference(os.path.join(bin_dir, 'LeakingExceptions'))

from LeakingExceptions import ExceptionThrower

thrower = ExceptionThrower()

while True:
    try:
        thrower.ThrowException()
    except:
        pass

• in the task manager you can then watch the application to accumulate memory and never release it