Synchronise rtsim saves

server/src/rtsim/mod.rs

@@ -9,6 +9,7 @@ use common::{
     terrain::Block,
 };
 use common_ecs::dispatch;
+use crossbeam_channel::{unbounded, Receiver, Sender};
 use enum_map::EnumMap;
 use rtsim::{
     data::{npc::SimulationMode, Data},
@@ -21,6 +22,7 @@ use std::{
     fs::{self, File},
     io,
     path::PathBuf,
+    thread::{self, JoinHandle},
     time::Instant,
 };
 use tracing::{debug, error, info, trace, warn};
@@ -31,6 +33,7 @@ pub struct RtSim {
     file_path: PathBuf,
     last_saved: Option<Instant>,
     state: RtState,
+    save_thread: Option<(Sender<Data>, JoinHandle<()>)>,
 }
 
 impl RtSim {
@@ -114,6 +117,7 @@ impl RtSim {
                 |_| None,
             ))),
             file_path,
+            save_thread: None,
         };
 
         rule::start_rules(&mut this.state);
@@ -189,42 +193,32 @@ impl RtSim {
         );
     }
 
-    pub fn save(&mut self, /* slowjob_pool: &SlowJobPool, */ wait_until_finished: bool) {
+    pub fn save(&mut self, wait_until_finished: bool) {
         debug!("Saving rtsim data...");
+
+        // Create the save thread if it doesn't already exist
+        // TODO: Use the slow job pool eventually
+        let (tx, _) = self.save_thread.get_or_insert_with(|| {
+            trace!("Starting rtsim data save thread...");
+            let (tx, rx) = unbounded();
             let file_path = self.file_path.clone();
-        let data = self.state.data().clone();
+            (tx, thread::spawn(move || save_thread(file_path, rx)))
-        trace!("Starting rtsim data save job...");
-        // TODO: Use slow job
-        // slowjob_pool.spawn("RTSIM_SAVE", move || {
-        let handle = std::thread::spawn(move || {
-            if let Err(e) = file_path
-                .parent()
-                .map(|dir| {
-                    fs::create_dir_all(dir)?;
-                    // We write to a temporary file and then rename to avoid corruption.
-                    Ok(dir.join(&file_path))
-                })
-                .unwrap_or(Ok(file_path))
-                .map(|file_path| AtomicFile::new(file_path, OverwriteBehavior::AllowOverwrite))
-                .map_err(|e: io::Error| Box::new(e) as Box<dyn Error>)
-                .and_then(|file| {
-                    debug!("Writing rtsim data to file...");
-                    file.write(move |file| -> Result<(), rtsim::data::WriteError> {
-                        data.write_to(io::BufWriter::new(file))?;
-                        // file.flush()?;
-                        Ok(())
-                    })?;
-                    drop(file);
-                    debug!("Rtsim data saved.");
-                    Ok(())
-                })
-            {
-                error!("Saving rtsim data failed: {}", e);
-            }
         });
 
+        // Send rtsim data to the save thread
+        if let Err(err) = tx.send(self.state.data().clone()) {
+            error!("Failed to perform rtsim save: {}", err);
+        }
+
+        // If we need to wait until the save thread has done its work (due to, for
+        // example, server shutdown) then do that.
         if wait_until_finished {
+            if let Some((tx, handle)) = self.save_thread.take() {
+                drop(tx);
+                info!("Waiting for rtsim save thread to finish...");
                 handle.join().expect("Save thread failed to join");
+                info!("Rtsim save thread finished.");
+            }
         }
 
         self.last_saved = Some(Instant::now());
@@ -242,6 +236,35 @@ impl RtSim {
     }
 }
 
+fn save_thread(file_path: PathBuf, rx: Receiver<Data>) {
+    while let Ok(data) = rx.recv() {
+        if let Err(e) = file_path
+            .parent()
+            .map(|dir| {
+                fs::create_dir_all(dir)?;
+                // We write to a temporary file and then rename to avoid corruption.
+                Ok(dir.join(&file_path))
+            })
+            .unwrap_or_else(|| Ok(file_path.clone()))
+            .map(|file_path| AtomicFile::new(file_path, OverwriteBehavior::AllowOverwrite))
+            .map_err(|e: io::Error| Box::new(e) as Box<dyn Error>)
+            .and_then(|file| {
+                debug!("Writing rtsim data to file...");
+                file.write(move |file| -> Result<(), rtsim::data::WriteError> {
+                    data.write_to(io::BufWriter::new(file))?;
+                    // file.flush()?;
+                    Ok(())
+                })?;
+                drop(file);
+                debug!("Rtsim data saved.");
+                Ok(())
+            })
+        {
+            error!("Saving rtsim data failed: {}", e);
+        }
+    }
+}
+
 pub struct ChunkStates(pub Grid<Option<LoadedChunkState>>);
 
 pub struct LoadedChunkState {