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//! Idiomatic Rust wrappers for N-API threadsafe functions
use std::{
ffi::c_void,
mem::MaybeUninit,
ptr,
sync::{Arc, Mutex},
};
use super::{bindings as napi, no_panic::FailureBoundary, raw::Env};
const BOUNDARY: FailureBoundary = FailureBoundary {
both: "A panic and exception occurred while executing a `neon::event::Channel::send` callback",
exception: "An exception occurred while executing a `neon::event::Channel::send` callback",
panic: "A panic occurred while executing a `neon::event::Channel::send` callback",
};
#[derive(Debug)]
struct Tsfn(napi::ThreadsafeFunction);
unsafe impl Send for Tsfn {}
unsafe impl Sync for Tsfn {}
#[derive(Debug)]
/// Threadsafe Function encapsulate a Rust function pointer and N-API threadsafe
/// function for scheduling tasks to execute on a JavaScript thread.
pub struct ThreadsafeFunction<T> {
tsfn: Tsfn,
is_finalized: Arc<Mutex<bool>>,
callback: fn(Option<Env>, T),
}
#[derive(Debug)]
struct Callback<T> {
callback: fn(Option<Env>, T),
data: T,
}
/// Error returned when scheduling a threadsafe function with some data
pub struct CallError;
impl<T: Send + 'static> ThreadsafeFunction<T> {
/// Creates a new unbounded N-API Threadsafe Function
/// Safety: `Env` must be valid for the current thread
pub unsafe fn new(env: Env, callback: fn(Option<Env>, T)) -> Self {
Self::with_capacity(env, 0, callback)
}
/// Creates a bounded N-API Threadsafe Function
/// Safety: `Env` must be valid for the current thread
pub unsafe fn with_capacity(
env: Env,
max_queue_size: usize,
callback: fn(Option<Env>, T),
) -> Self {
let mut result = MaybeUninit::uninit();
let is_finalized = Arc::new(Mutex::new(false));
assert_eq!(
napi::create_threadsafe_function(
env,
std::ptr::null_mut(),
std::ptr::null_mut(),
super::string(env, "neon threadsafe function"),
max_queue_size,
// Always set the reference count to 1. Prefer using
// Rust `Arc` to maintain the struct.
1,
Arc::into_raw(is_finalized.clone()) as *mut _,
Some(Self::finalize),
std::ptr::null_mut(),
Some(Self::callback),
result.as_mut_ptr(),
),
Ok(()),
);
Self {
tsfn: Tsfn(result.assume_init()),
is_finalized,
callback,
}
}
/// Schedule a threadsafe function to be executed with some data
pub fn call(
&self,
data: T,
is_blocking: Option<napi::ThreadsafeFunctionCallMode>,
) -> Result<(), CallError> {
let is_blocking = is_blocking.unwrap_or(napi::ThreadsafeFunctionCallMode::Blocking);
let callback = Box::into_raw(Box::new(Callback {
callback: self.callback,
data,
}));
// Hold the lock before entering `call_threadsafe_function` so that
// `finalize_cb` would never complete.
let mut is_finalized = self.is_finalized.lock().unwrap();
let status = {
if *is_finalized {
Err(napi::Status::Closing)
} else {
unsafe {
napi::call_threadsafe_function(self.tsfn.0, callback as *mut _, is_blocking)
}
}
};
match status {
Ok(()) => Ok(()),
Err(status) => {
// Prevent further calls to `call_threadsafe_function`
if status == napi::Status::Closing {
*is_finalized = true;
}
// If the call failed, the callback won't execute
let _ = unsafe { Box::from_raw(callback) };
Err(CallError)
}
}
}
/// References a threadsafe function to prevent exiting the event loop until it has been dropped. (Default)
/// Safety: `Env` must be valid for the current thread
pub unsafe fn reference(&self, env: Env) {
napi::ref_threadsafe_function(env, self.tsfn.0).unwrap();
}
/// Unreferences a threadsafe function to allow exiting the event loop before it has been dropped.
/// Safety: `Env` must be valid for the current thread
pub unsafe fn unref(&self, env: Env) {
napi::unref_threadsafe_function(env, self.tsfn.0).unwrap();
}
// Provides a C ABI wrapper for a napi callback notifying us about tsfn
// being finalized.
unsafe extern "C" fn finalize(_env: Env, data: *mut c_void, _hint: *mut c_void) {
let is_finalized = Arc::from_raw(data as *mut Mutex<bool>);
*is_finalized.lock().unwrap() = true;
}
// Provides a C ABI wrapper for invoking the user supplied function pointer
// On panic or exception, creates a fatal exception of the form:
// Error(msg: string) {
// // Exception thrown
// cause?: Error,
// // Panic occurred
// panic?: Error(msg: string) {
// // Opaque panic type if it wasn't a string
// cause?: JsBox<Panic>
// }
// }
unsafe extern "C" fn callback(
env: Env,
_js_callback: napi::Value,
_context: *mut c_void,
data: *mut c_void,
) {
let Callback { callback, data } = *Box::from_raw(data as *mut Callback<T>);
BOUNDARY.catch_failure(env, None, move |env| {
callback(env, data);
ptr::null_mut()
});
}
}
impl<T> Drop for ThreadsafeFunction<T> {
fn drop(&mut self) {
let is_finalized = self.is_finalized.lock().unwrap();
// tsfn was already finalized by `Environment::CleanupHandles()` in Node.js
if *is_finalized {
return;
}
unsafe {
debug_assert_eq!(
napi::release_threadsafe_function(
self.tsfn.0,
napi::ThreadsafeFunctionReleaseMode::Release,
),
Ok(())
);
};
}
}