Light improvements

Trying to solve random hangs we've seen, ensuring that this part of code isnt the culprit

also fixing a vanilla bug reportedby PhiPro where tickets are released too early
hoping this reduces amount of incorrect light issues.

Spigot-Server-Patches/0497-Optimize-Light-Engine.patch

@@ -1027,7 +1027,7 @@ index a35e7b392c74fadf2760d1fc2021e98d33858cb5..944094e8e770cc8c0205ef2aa6c48fff
                                  lightenginelayer.a(Long.MAX_VALUE, l3, 15, false);
                              }
 diff --git a/src/main/java/net/minecraft/server/LightEngineThreaded.java b/src/main/java/net/minecraft/server/LightEngineThreaded.java
-index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb726b95b6 100644
+index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..fd0beefb900c064d3c35a3d2f79f5b7d9c1287bb 100644
 --- a/src/main/java/net/minecraft/server/LightEngineThreaded.java
 +++ b/src/main/java/net/minecraft/server/LightEngineThreaded.java
 @@ -1,6 +1,7 @@
@@ -1038,7 +1038,7 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
  import it.unimi.dsi.fastutil.objects.ObjectArrayList;
  import it.unimi.dsi.fastutil.objects.ObjectList;
  import it.unimi.dsi.fastutil.objects.ObjectListIterator;
-@@ -15,15 +16,158 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
+@@ -15,15 +16,149 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
  
      private static final Logger LOGGER = LogManager.getLogger();
      private final ThreadedMailbox<Runnable> b;
@@ -1048,7 +1048,7 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
 +    private static final int MAX_PRIORITIES = PlayerChunkMap.GOLDEN_TICKET + 2;
 +
 +    private boolean isChunkLightStatus(long pair) {
-+        PlayerChunk playerChunk = playerChunkMap.getUpdatingChunk(pair);
++        PlayerChunk playerChunk = playerChunkMap.getVisibleChunk(pair);
 +        if (playerChunk == null) {
 +            return false;
 +        }
@@ -1084,7 +1084,6 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
 +    // Retain the chunks priority level for queued light tasks
 +    class LightQueue {
 +        private int size = 0;
-+        private int lowestPriority = MAX_PRIORITIES;
 +        private final Long2ObjectLinkedOpenHashMap<ChunkLightQueue>[] buckets = new Long2ObjectLinkedOpenHashMap[MAX_PRIORITIES];
 +        private final java.util.concurrent.ConcurrentLinkedQueue<PendingLightTask> pendingTasks = new java.util.concurrent.ConcurrentLinkedQueue<>();
 +        private final java.util.concurrent.ConcurrentLinkedQueue<Runnable> priorityChanges = new java.util.concurrent.ConcurrentLinkedQueue<>();
@@ -1105,11 +1104,6 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
 +                        remove.post.addAll(existing.post);
 +                    }
 +                }
-+                if (!this.buckets[priority].isEmpty()) {
-+                    if (lowestPriority > priority) {
-+                        lowestPriority = priority;
-+                    }
-+                }
 +            });
 +        }
 +
@@ -1136,10 +1130,6 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
 +            if (update.fastUpdate) {
 +                lightQueue.shouldFastUpdate = true;
 +            }
-+
-+            if (this.lowestPriority > priority) {
-+                this.lowestPriority = priority;
-+            }
 +        }
 +
 +        public final boolean isEmpty() {
@@ -1161,11 +1151,12 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
 +            }
 +            boolean hasWork = false;
 +            Long2ObjectLinkedOpenHashMap<ChunkLightQueue>[] buckets = this.buckets;
++            int lowestPriority = 0;
 +            while (lowestPriority < MAX_PRIORITIES && !isEmpty()) {
 +                Long2ObjectLinkedOpenHashMap<ChunkLightQueue> bucket = buckets[lowestPriority];
 +                if (bucket.isEmpty()) {
 +                    lowestPriority++;
-+                    if (hasWork && lowestPriority <= 3) {
++                    if (hasWork && lowestPriority <= 5) {
 +                        return true;
 +                    } else {
 +                        continue;
@@ -1200,7 +1191,7 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
          this.e = mailbox;
          this.b = threadedmailbox;
      }
-@@ -110,13 +254,9 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
+@@ -110,13 +245,9 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
      }
  
      private void a(int i, int j, IntSupplier intsupplier, LightEngineThreaded.Update lightenginethreaded_update, Runnable runnable) {
@@ -1217,7 +1208,7 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
      }
  
      @Override
-@@ -133,8 +273,20 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
+@@ -133,8 +264,19 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
      public CompletableFuture<IChunkAccess> a(IChunkAccess ichunkaccess, boolean flag) {
          ChunkCoordIntPair chunkcoordintpair = ichunkaccess.getPos();
  
@@ -1231,7 +1222,6 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
 +        boolean[] skippedPre = {false};
 +        this.queue.addChunk(pair, prioritySupplier, SystemUtils.a(() -> {
 +            if (!isChunkLightStatus(pair)) {
-+                this.d.c(chunkcoordintpair); // copied from end of method to release light ticket
 +                future.complete(ichunkaccess);
 +                skippedPre[0] = true;
 +                return;
@@ -1240,18 +1230,19 @@ index f8c2b957bb5b38f05251cccf5137a9c23262c3d6..ec8498c3db7a8d417f27eed5d3af38cb
              ChunkSection[] achunksection = ichunkaccess.getSections();
  
              for (int i = 0; i < 16; ++i) {
-@@ -152,55 +304,47 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
+@@ -152,55 +294,48 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
                  });
              }
  
 -            this.d.c(chunkcoordintpair);
-+            this.d.c(chunkcoordintpair); // Paper - if change, copy into !isChunkLightStatus above
++            // this.d.c(chunkcoordintpair); // Paper - move into post task below
          }, () -> {
              return "lightChunk " + chunkcoordintpair + " " + flag;
 -        }));
 -        return CompletableFuture.supplyAsync(() -> {
 +            // Paper start  - merge the 2 together
 +        }), () -> {
++            this.d.c(chunkcoordintpair); // Paper - release light tickets as post task to ensure they stay loaded until fully done
 +            if (skippedPre[0]) return; // Paper - future's already complete
              ichunkaccess.b(true);
              super.b(chunkcoordintpair, false);
@@ -1338,7 +1329,7 @@ index ff00830b95a17f66d0c913087492dbf4b066df8a..4085426af03f032cf405bdfd1e40a8e5
      private static final int nibbleBucketSizeMultiplier = Integer.getInteger("Paper.nibbleBucketSize", 3072);
      private static final int maxPoolSize = Integer.getInteger("Paper.maxNibblePoolSize", (int) Math.min(6, Math.max(1, Runtime.getRuntime().maxMemory() / 1024 / 1024 / 1024)) * (nibbleBucketSizeMultiplier * 8));
 diff --git a/src/main/java/net/minecraft/server/PlayerChunk.java b/src/main/java/net/minecraft/server/PlayerChunk.java
-index 27c4dc6caf7b6303766dd8eee4812209600cd728..676f0d28b0c8a590c6429a93902953636b3c1f11 100644
+index 1f14ebf09de9f2671b30498ea8fd66750ae85dff..de1e409dc5161371c6f14d036603be448fcd3e26 100644
 --- a/src/main/java/net/minecraft/server/PlayerChunk.java
 +++ b/src/main/java/net/minecraft/server/PlayerChunk.java
 @@ -724,6 +724,7 @@ public class PlayerChunk {