Another disk indirectio attempt

crates/librqbit/src/torrent_state/live/mod.rs

@@ -176,6 +176,8 @@ pub struct TorrentStateLive {
     up_speed_estimator: SpeedEstimator,
     cancellation_token: CancellationToken,
 
+    disk_work_queue_tx: tokio::sync::mpsc::Sender<Box<dyn FnOnce() + Send + Sync>>,
+
     pub(crate) streams: Arc<TorrentStreams>,
 }
 
@@ -207,6 +209,8 @@ impl TorrentStateLive {
             pri
         };
 
+        let (disk_work_queue_tx, mut disk_work_queue_rx) = tokio::sync::mpsc::channel(2048);
+
         let state = Arc::new(TorrentStateLive {
             meta: paused.info.clone(),
             peers: Default::default(),
@@ -229,8 +233,21 @@ impl TorrentStateLive {
             up_speed_estimator,
             cancellation_token,
             streams: paused.streams,
+            disk_work_queue_tx,
         });
 
+        if paused.info.options.defer_writes {
+            state.spawn(
+                error_span!(parent: state.meta.span.clone(), "disk_writer"),
+                async move {
+                    while let Some(work_unit) = disk_work_queue_rx.recv().await {
+                        tokio::runtime::Handle::current().spawn_blocking(work_unit);
+                    }
+                    Ok(())
+                },
+            );
+        }
+
         state.spawn(
             error_span!(parent: state.meta.span.clone(), "speed_estimator_updater"),
             {
@@ -1482,6 +1499,7 @@ impl PeerHandler {
             let counters = self.counters.clone();
             let piece = piece.clone_to_owned();
             let tx = self.tx.clone();
+            let disk_work_queue_tx = state.disk_work_queue_tx.clone();
 
             let work = move || {
                 if let Err(e) = write_to_disk(
@@ -1495,7 +1513,7 @@ impl PeerHandler {
                     let _ = tx.send(WriterRequest::Disconnect(Err(e)));
                 }
             };
-            tokio::runtime::Handle::current().spawn_blocking(work);
+            disk_work_queue_tx.blocking_send(Box::new(work))?;
         } else {
             self.state
                 .meta