Dynamo: [BUG] Node failing downstream causes Null's upstream

[Amoursol]

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Dynamo version

Dynamo Core 2.0.1.5055
Dynamo Revit 2.0.1.5065

Operating system

Windows 10

What did you do?

I have broken some of my Python code downstream (Causing the node to error out). This resulted in prior Python nodes breaking (Refer to the attached GIF).

What did you expect to see?

All upstream Python code executing correctly. An error message on the failing node to simply point out the error at that point.

What did you see instead?

Downstream Python node failure causes 'null' returns upstream.

1) Execute Graph containing Python node [Curve Offset Node] returns Curves. Correctly functioning.
2) Plug in results of Python node [Curve Offset Node] to another Python node [Independently Failing Node] which fails independently.
3) [Result] Python node [Curve Offset Node] now returns Null. Any additional output has a 'hover' return of a List with the correct item count, but a 'pinned' return of Null.
4) Unplug Python node [Curve Offset Node] from Python node [Independently Failing Node] results in Curves returning again.

[Amoursol]

@aparajit-pratap @mjkkirschner @Racel This is some funky behaviour :)

[mjkkirschner]

It depends what your two python nodes do - most of our libraries are immutable, but you could do anything in python(including disposing geometry that another node produced). Can you share the .dyn or a smaller sample that reproduces the issue?

[MarkThorley]

Hi Mike,
We found the issue and its related to disposing of geometry that was created outside of the python node, that is to be used upstream in the graph. We assumed disposing of geometry in a python node was only relative to the python node but it seems it disposes of the geometry from the entire graph memory. Video to follow

[MarkThorley]

Files.zip

[mjkkirschner]

Nope, if you pass in geometry to your python node and call dispose on it - you're disposing it.

You must be careful not to dispose objects that are referenced in other places.
When you create geometry with our library you usually get a new piece of geometry back, as protogeometry is designed to return immutable objects. If you want to avoid modifying geometry objects you pass into your code you can keep track of those objects and use reference equality to avoid them or you our can copy all the geometry objects at the start of your code - you can do this by translating them by (0,0,0).

[MarkThorley]

Thanks for clarifying. Would be worth adding these notes to the documentation around disposing in the primer etc

[Amoursol]

Seconding @MarkThorley 's suggestion - this sounds like a messaging issue. Assumptions were that downstream graphs couldn't affect upstream nodes. In retrospect very obvious but not so at the time.

[johnpierson]

Thanks for clarifying. Would be worth adding these notes to the documentation around disposing in the primer etc

I would say that it should get added to the wiki. This sounds like a rather advanced concept for the primer?

The ZeroTouch section already mentions some of the considerations with Disposing as well.
https://github.com/DynamoDS/Dynamo/wiki/Zero-Touch-Plugin-Development