rust-lang
What is a good strategy to extract information out of `ParseCallbacks`?
I'd like to extract information from ParseCallbacks so that it can be used later in the build script.
For example:
I have three C macros:
VERSION_MAJORVERSION_MINORVERSION_PATCH
which all define a number and so get forwarded to ParseCallbacks::int_macro. Now in my implementation of that callback, I want to capture these integers for use later in the build script.
Currently, as I see it, the only option is to use Atomic* or Mutex as the bound on ParseCallbacks specifies UnwindSafe which references to types with interior mutability are not, and the callbacks themselves only get a shared reference to self.
This works but is not pretty and may incur performance penalties for Mutex.
So my questions are:
- What is the preferred strategy for doing something like that?
(More so with a less trivial example that requires more complex data e.g.
ParseCallbacks::func_macro) - Why do these functions not get a mutable reference to self if the callbacks don't need to be
Send/Sync?
Generally interior mutability is the way we've been doing this, yeah. So a RefCell or so perhaps.
The callbacks don't take mutable references because the BindgenContext they are stored in is immutable as well. We could internally use RefCell<Box<ParseCallbacks>> or so to allow that and move the burden to bindgen.
Thanks for the response.
It seems like I missed RefCell (I only tried Cell and because that's not UnwindSafe thought that all *Cell types wouldn't work).
We could internally use
RefCell<Box<ParseCallbacks>>or so to allow that and move the burden to bindgen.
That would be nice.
Until then I'll make a PR to mention this in the docs (if that's okay), because I didn't find this mentioned even though ParseCallbacks::func_macro exists only to extract information out of bindgen.
You cannot use RefCell either because it contains a Cell<isize> field. and as you already mentioned Cell does not implement RefUnwindSafe.
I opened #2317 which removes this restriction and uses panic hooks in the CLI. I'm not sure if anyone relies on catch_unwind to run bindgen and do something else if it panics but they should be able to achieve the same using threads anyway iiuc.
