[Python.NET] Memory management when embedding python.

Thomas Lundgaard Hansen Thomas.Lundgaard at 3shape.com
Wed Sep 11 03:58:34 EDT 2019

Thank you. I am fine with a little delay before the objects are collected, I just wanted to make sure there are no other side effects by not calling Dispose() on the objects.

On a side node, regarding GC.AddMemoryPressure: PyObjects have some (possibly large) amount of backing unmanaged memory. The .NET garbage collector does not know about this memory and thus cannot take it into account when deciding when the GC should be triggered. AddMemoryPressure allows you to tell the .NET GC about the unmanaged backing memory. However, PythonNET may not know the amount of memory that has been allocated when constructing python objects.

Best regards,
Thomas Lundgaard Hansen

From: PythonDotNet <pythondotnet-bounces+thomas.lundgaard=3shape.com at python.org> On Behalf Of Li Amos
Sent: Sunday, September 8, 2019 8:12 PM
To: A list for users and developers of Python for .NET <pythondotnet at python.org>
Subject: Re: [Python.NET] Memory management when embedding python.

If you want to dispose the PyObject and reduce the reference count immediately you should call `Dispose` manually or use `using` statement.
Otherwise, GC will take care of it although it would be a little delay, you can adjust ` Finalizer.Instance.Threshold ` for reducing the delay, it refers how many PyObjects will be collect at once after GC mark them as garbage.

About `GC.AddMemoryPressure`, there's no relate with it, PyObject only contains pointers of CPython, it doesn't allocate any unmanaged memory, thus GC know the objects' size.

From: Denis Akhiyarov<mailto:denis.akhiyarov at gmail.com>
Sent: Sunday, September 8, 2019 23:43
To: A list for users and developers of Python for .NET<mailto:pythondotnet at python.org>
Subject: Re: [Python.NET] Memory management when embedding python.

There is a lot more going on this topic of GC in GitHub repo, but I'm not involved with the project anymore.

Anyway if anyone is interested in moderating this mailing list, please let me know.


On Sun, Sep 8, 2019, 10:35 AM Thomas Lundgaard Hansen <Thomas.Lundgaard at 3shape.com<mailto:Thomas.Lundgaard at 3shape.com>> wrote:

I am embedding Python into a .NET (C#) application. For the purpose of this discussion my code is
like the example given here:
(except that I am working with arrays of a substantial size).

Each of the "dynamic" variables created in that example are of the .NET type PyObject, which is
a disposable type. The code in the example does not call Dispose() on these objects and it would
indeed be very inconvenient to do so.

Whats the best practice here and what considerations went into this design? Can we expect that
the only unmanged resources held by PyObject's are unmanaged memory? (Unless, of course, the
PyObject represents a system resource like a file or network stream).

Has it been considered to use GC.AddMemoryPressure when PyObjects are backed by a large
amount of unmanaged memory?

Thomas Lundgaard Hansen

Python.NET mailing list - PythonDotNet at python.org<mailto:PythonDotNet at python.org>

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