"We need developers to be able to use these libraries safely and easily without sacrificing the benefits that Rust offers. Inversely, if we want to see Rust components integrated with our larger C++ binaries, we need smart runtime interoperability in asynchronous code. Facebook's servers are highly distributed and heavily threaded. Rust tasks need to play nicely on a C++ threadpool and safely share synchronization primitives and I/O resources," Meta engineers recently explained.