Investigate usage of cgo.Handle for callback handling

[dignifiedquire]

Should look into using https://pkg.go.dev/runtime/[email protected]#Handle for callback handling, which is the recommended way of dealing with callbacks since go 1.17

https://github.com/golang/go/wiki/cgo#function-variables for reference

[arg0d]

Looks like a good idea. Would allow to get rid of callback table from Go bindings. But I wonder if the semantics of Handle are safe, i.e. use after calling Handle.Delete(), callling Handle.Delete() multiple times. If these are defined behaviors and result in a panic (unlike C where it would be undefined behavior), then I think we can definitely switch to use Handle.

[dignifiedquire]

@arg0d why did you close the issue?

[dignifiedquire]

But I wonder if the semantics of Handle are safe, i.e. use after calling Handle.Delete(), callling Handle.Delete() multiple times.

It seems these are meant to be safe. From the docs of Delete: "The method panics if the handle is invalid."

[dignifiedquire]

And the same for Value:

Value returns the associated Go value for a valid handle.

The method panics if the handle is invalid.

[arg0d]

😅 I somehow closed it by accident

[dignifiedquire]

Implementation of cgo.Handle is done using a global https://pkg.go.dev/sync#Map