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//! Small utility to correctly spawn crossbeam-channel based worker threads.
use std::thread;
use crossbeam_channel::{bounded, unbounded, Receiver, Sender};
/// Like `std::thread::JoinHandle<()>`, but joins thread in drop automatically.
pub struct ScopedThread {
// Option for drop
inner: Option<thread::JoinHandle<()>>,
}
impl Drop for ScopedThread {
fn drop(&mut self) {
let inner = self.inner.take().unwrap();
let name = inner.thread().name().unwrap().to_string();
log::info!("waiting for {} to finish...", name);
let res = inner.join();
log::info!(".. {} terminated with {}", name, if res.is_ok() { "ok" } else { "err" });
// escalate panic, but avoid aborting the process
if let Err(e) = res {
if !thread::panicking() {
panic!(e)
}
}
}
}
impl ScopedThread {
pub fn spawn(name: &'static str, f: impl FnOnce() + Send + 'static) -> ScopedThread {
let inner = thread::Builder::new().name(name.into()).spawn(f).unwrap();
ScopedThread { inner: Some(inner) }
}
}
/// A wrapper around event-processing thread with automatic shutdown semantics.
pub struct Worker<I, O> {
// XXX: field order is significant here.
//
// In Rust, fields are dropped in the declaration order, and we rely on this
// here. We must close input first, so that the `thread` (who holds the
// opposite side of the channel) noticed shutdown. Then, we must join the
// thread, but we must keep out alive so that the thread does not panic.
//
// Note that a potential problem here is that we might drop some messages
// from receiver on the floor. This is ok for rust-analyzer: we have only a
// single client, so, if we are shutting down, nobody is interested in the
// unfinished work anyway!
sender: Sender<I>,
_thread: ScopedThread,
receiver: Receiver<O>,
}
impl<I, O> Worker<I, O> {
pub fn spawn<F>(name: &'static str, buf: usize, f: F) -> Worker<I, O>
where
F: FnOnce(Receiver<I>, Sender<O>) + Send + 'static,
I: Send + 'static,
O: Send + 'static,
{
// Set up worker channels in a deadlock-avoiding way. If one sets both input
// and output buffers to a fixed size, a worker might get stuck.
let (sender, input_receiver) = bounded::<I>(buf);
let (output_sender, receiver) = unbounded::<O>();
let _thread = ScopedThread::spawn(name, move || f(input_receiver, output_sender));
Worker { sender, _thread, receiver }
}
}
impl<I, O> Worker<I, O> {
pub fn sender(&self) -> &Sender<I> {
&self.sender
}
pub fn receiver(&self) -> &Receiver<O> {
&self.receiver
}
}
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