GlobalRef should be Send + Sync? about jni-rs

[dmitry-timofeev]

Definitely, GlobalRefs are thread-safe, and there is already a workaround to access the same underlying global reference (C-JNI) from different threads by cloning it, if I understand correctly. @alexander-irbis , do you remember if there is any reason against making it Sync?

[skletsun]

The definition of Sync from its source file:

The precise definition is: a type T is Sync if and only if &T is Send. In other words, if there is no possibility of undefined behavior (including data races) when passing &T references between threads.

The methods of GlobalRef provide correct references to correct entities between threads and provide no interior mutability in a non-thread-safe form. With regards to this, I believe that it is safe for GlobalRef to implement the Sync trait as well.