I have a C function which takes a callback and invokes it on another thread:
void call_in_new_thread(void (*callback)()) {
// spawn a new thread and call `callback` in it ...
}
I want to call this function from JavaScript via Node-FFI, passing a JavaScript function to it:
var callbackType = 'pointer'
var lib = ffi.Library('mylib', {
'call_in_new_thread': [ 'void', [ callbackType ] ],
})
var callback = ffi.Callback('void', [ 'void' ], function() {
// which thread I'm in now?
console.log("hello!")
})
lib.call_in_new_thread(callback)
Is this valid? Is it thread safe? Which thread does the JavaScript callback actually execute in: the Node.js main thread, or in the thread created by the FFI library? Does Node-FFI synchronize the call somehow?
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:
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