Is it safe to pass a JavaScript callback to an FFI function which calls it in another thread?

Question

I have a C function which takes a callback and invokes it on another thread:

void call_in_new_thread(void (*callback)())         


        

Answer 1

I hacked together a quick demo to test this out. It's using Rust instead of C for the native part, but that should be equivalent as Rust can compile to a normal shared library.

After running the demo, I would answer my own questions like this:

• Yes, it seems to be valid and safe
• The JavaScript callback gets executed in the main thread
• Node-FFI seems to handle the synchronization by pushing the JavaScript callback to a queue which gets popped on the main thread