Custom References with Magic Cookies

[JamesWiresmith]

LabVIEW references are all handled through something called Cookie Jars.

The API for this is undocumented but there is a public reference as it is used for the OpenG Zip library with the C source at https://github.com/Open-G/lvzip-library/blob/c6ae51670d185d062002d8fae7d4e4c7ec425b1b/c_source/refnum.c#L41

This would always be in a questionable place support wise but it would be a massive bonus since we could retain Rust drop semantics automatically and detect invalid references.

[JamesWiresmith]

It could be that EDVR supports most of these cases anyway such as in #10

[JamesWiresmith]

Having spoken to a few people EDVRs are really intended for data access. We can support them for array accesses but these references are more the intended use case here.

[j-medland]

As with EDVRs in #10, my rust skills aren't there yet but here is a simple example of registering a CleanupProc to perform automatic cleanup of a C++ allocated resource.

https://github.com/j-medland/labview-cleanup-proc-example

To my mind - it might not be worth working with cookie jars. Working with raw pointers/handles wrapped into an LVClass is my preference but if you want a classic refnum and to support 64-bit then you can implement a simple global map on the C++ side which uses 32-bit keys to get to the raw 32/64-bit object pointers.

[JamesWiresmith]

Thanks for sharing. I think they aren't critical to success but I do think that having some mechanism will avoid issues with LabVIEW APIs.