It's comment is:
/* arg_hash maps long values corresponding to the addresses of an
* UnwindArgs object and its CBarg and UPTarg fields, to the
* UnwindArgs object itself. This enables us to choose the right
* argument to pass to callbacks even when one callback calls
* another. */
which makes me wonder if the binding is single threaded.
Can this bug and the comment be updated with a more detailed description.
Class got completely rewritten and no arg_hash map is being used anymore.