Fix plotting getting stuck

crates/subspace-farmer/src/single_disk_farm/plotting.rs

@@ -6,7 +6,7 @@ use crate::single_disk_farm::metrics::{SectorState, SingleDiskFarmMetrics};
 use crate::single_disk_farm::{
     BackgroundTaskError, Handlers, PlotMetadataHeader, RESERVED_PLOT_METADATA,
 };
-use async_lock::{Mutex as AsyncMutex, RwLock as AsyncRwLock, Semaphore};
+use async_lock::{Mutex as AsyncMutex, RwLock as AsyncRwLock, Semaphore, SemaphoreGuard};
 use futures::channel::{mpsc, oneshot};
 use futures::stream::FuturesOrdered;
 use futures::{select, FutureExt, SinkExt, StreamExt};
@@ -123,8 +123,30 @@ where
         max_plotting_sectors_per_farm,
     } = plotting_options;
 
+    let sector_plotting_options = &sector_plotting_options;
     let plotting_semaphore = Semaphore::new(max_plotting_sectors_per_farm.get());
     let mut sectors_being_plotted = FuturesOrdered::new();
+    // Channel size is intentionally unbounded for easier analysis, but it is bounded by plotting
+    // semaphore in practice due to permit stored in `SectorPlottingResult`
+    let (sector_plotting_result_sender, mut sector_plotting_result_receiver) = mpsc::unbounded();
+    let process_plotting_result_fut = async move {
+        while let Some(sector_plotting_result) = sector_plotting_result_receiver.next().await {
+            process_plotting_result(
+                sector_plotting_result,
+                sectors_metadata,
+                sectors_being_modified,
+                &mut metadata_header,
+                Arc::clone(&sector_plotting_options.metadata_file),
+            )
+            .await?;
+        }
+
+        unreachable!(
+            "Stream will not end before the rest of the plotting process is shutting down"
+        );
+    };
+    let process_plotting_result_fut = process_plotting_result_fut.fuse();
+    let mut process_plotting_result_fut = pin!(process_plotting_result_fut);
 
     // Wait for new sectors to plot from `sectors_to_plot_receiver` and wait for sectors that
     // already started plotting to finish plotting and then update metadata header
@@ -138,7 +160,7 @@ where
                 let sector_index = sector_to_plot.sector_index;
                 let sector_plotting_init_fut = plot_single_sector(
                     sector_to_plot,
-                    &sector_plotting_options,
+                    sector_plotting_options,
                     sectors_metadata,
                     sectors_being_modified,
                     &plotting_semaphore,
@@ -168,25 +190,23 @@ where
                             break;
                         }
                         maybe_sector_plotting_result = sectors_being_plotted.select_next_some() => {
-                            process_plotting_result(
-                                maybe_sector_plotting_result?,
-                                sectors_metadata,
-                                sectors_being_modified,
-                                &mut metadata_header,
-                                Arc::clone(&sector_plotting_options.metadata_file)
-                            ).await?;
+                            sector_plotting_result_sender
+                                .unbounded_send(maybe_sector_plotting_result?)
+                                .expect("Sending means receiver is not dropped yet; qed");
+                        }
+                        result = process_plotting_result_fut => {
+                            return result;
                         }
                     }
                 }
             }
             maybe_sector_plotting_result = sectors_being_plotted.select_next_some() => {
-                process_plotting_result(
-                    maybe_sector_plotting_result?,
-                    sectors_metadata,
-                    sectors_being_modified,
-                    &mut metadata_header,
-                    Arc::clone(&sector_plotting_options.metadata_file)
-                ).await?;
+                sector_plotting_result_sender
+                    .unbounded_send(maybe_sector_plotting_result?)
+                    .expect("Sending means receiver is not dropped yet; qed");
+            }
+            result = process_plotting_result_fut => {
+                return result;
             }
         }
     }
@@ -195,7 +215,7 @@ where
 }
 
 async fn process_plotting_result(
-    sector_plotting_result: SectorPlottingResult,
+    sector_plotting_result: SectorPlottingResult<'_>,
     sectors_metadata: &AsyncRwLock<Vec<SectorMetadataChecksummed>>,
     sectors_being_modified: &AsyncRwLock<HashSet<SectorIndex>>,
     metadata_header: &mut PlotMetadataHeader,
@@ -205,6 +225,7 @@ async fn process_plotting_result(
         sector_metadata,
         replotting,
         last_queued,
+        plotting_permit,
     } = sector_plotting_result;
 
     let sector_index = sector_metadata.sector_index;
@@ -241,6 +262,8 @@ async fn process_plotting_result(
         }
     }
 
+    drop(plotting_permit);
+
     Ok(())
 }
 
@@ -250,10 +273,11 @@ enum PlotSingleSectorResult<F> {
     FatalError(PlottingError),
 }
 
-struct SectorPlottingResult {
+struct SectorPlottingResult<'a> {
     sector_metadata: SectorMetadataChecksummed,
     replotting: bool,
     last_queued: bool,
+    plotting_permit: SemaphoreGuard<'a>,
 }
 
 async fn plot_single_sector<'a, NC>(
@@ -262,7 +286,9 @@ async fn plot_single_sector<'a, NC>(
     sectors_metadata: &'a AsyncRwLock<Vec<SectorMetadataChecksummed>>,
     sectors_being_modified: &'a AsyncRwLock<HashSet<SectorIndex>>,
     plotting_semaphore: &'a Semaphore,
-) -> PlotSingleSectorResult<impl Future<Output = Result<SectorPlottingResult, PlottingError>> + 'a>
+) -> PlotSingleSectorResult<
+    impl Future<Output = Result<SectorPlottingResult<'a>, PlottingError>> + 'a,
+>
 where
     NC: NodeClient,
 {
@@ -478,12 +504,11 @@ where
             .sector_update
             .call_simple(&(sector_index, sector_state));
 
-        drop(plotting_permit);
-
         Ok(SectorPlottingResult {
             sector_metadata,
             replotting,
             last_queued,
+            plotting_permit,
         })
     })
 }