Fix panic when quitting application

crates/fj-host/src/evaluator.rs

@@ -6,7 +6,7 @@ use crate::{Error, Evaluation, Model};
 
 /// Evaluates a model in a background thread
 pub struct Evaluator {
- trigger_tx: Sender<()>,
+ trigger_tx: Sender<TriggerEvaluation>,
  event_rx: Receiver<ModelEvent>,
 }
 
@@ -16,24 +16,26 @@ impl Evaluator {
  let (event_tx, event_rx) = crossbeam_channel::bounded(0);
  let (trigger_tx, trigger_rx) = crossbeam_channel::bounded(0);
 
- thread::spawn(move || loop {
- let () = trigger_rx
- .recv()
- .expect("Expected channel to never disconnect");
-
- let evaluation = match model.evaluate() {
- Ok(evaluation) => evaluation,
- Err(err) => {
- event_tx
- .send(ModelEvent::Error(err))
- .expect("Expected channel to never disconnect");
- continue;
- }
- };
-
- event_tx
- .send(ModelEvent::Evaluation(evaluation))
- .expect("Expected channel to never disconnect");
+ thread::spawn(move || {
+ while let Ok(TriggerEvaluation) = trigger_rx.recv() {
+ let evaluation = match model.evaluate() {
+ Ok(evaluation) => evaluation,
+ Err(err) => {
+ event_tx
+ .send(ModelEvent::Error(err))
+ .expect("Expected channel to never disconnect");
+ continue;
+ }
+ };
+
+ event_tx
+ .send(ModelEvent::Evaluation(evaluation))
+ .expect("Expected channel to never disconnect");
+ }
+
+ // The channel is disconnected, which means this instance of
+ // `Evaluator`, as well as all `Sender`s created from it, have been
+ // dropped. We're done.
  });
 
  Self {
@@ -43,7 +45,7 @@ impl Evaluator {
  }
 
  /// Access a channel for triggering evaluations
- pub fn trigger(&self) -> Sender<()> {
+ pub fn trigger(&self) -> Sender<TriggerEvaluation> {
  self.trigger_tx.clone()
  }
 
@@ -53,6 +55,9 @@ impl Evaluator {
  }
 }
 
+/// Command received by [`Evaluator`] through its channel
+pub struct TriggerEvaluation;
+
 /// An event emitted by [`Evaluator`]
 pub enum ModelEvent {
  /// The model has been evaluated

crates/fj-host/src/watcher.rs

@@ -2,7 +2,7 @@ use std::{collections::HashSet, ffi::OsStr, path::Path, thread};
 
 use notify::Watcher as _;
 
-use crate::{Error, Evaluator};
+use crate::{evaluator::TriggerEvaluation, Error, Evaluator};
 
 /// Watches a model for changes, reloading it continually
 pub struct Watcher {
@@ -65,7 +65,9 @@ impl Watcher {
  // application is being shut down.
  //
  // Either way, not much we can do about it here.
- watch_tx.send(()).expect("Channel is disconnected");
+ watch_tx
+ .send(TriggerEvaluation)
+ .expect("Channel is disconnected");
  }
  },
  )?;
@@ -82,7 +84,9 @@ impl Watcher {
  // Will panic, if the receiving end has panicked. Not much we can do
  // about that, if it happened.
  thread::spawn(move || {
- watch_tx_2.send(()).expect("Channel is disconnected")
+ watch_tx_2
+ .send(TriggerEvaluation)
+ .expect("Channel is disconnected")
  });
 
  Ok(Self {