Fix Light Prioritization Issues

Ensures light priorities are properly processed before processing new
work, skipping the threads queue.

also stops processing work on task submission.

Also drops dead chunks light work to not waste time on work thats going to be discarded.

Fixes #3986
Fixes #4002
Fixes #3951

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

@@ -1030,18 +1030,18 @@ diff --git a/src/main/java/net/minecraft/server/LightEngineThreaded.java b/src/m
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
 --- a/src/main/java/net/minecraft/server/LightEngineThreaded.java
 +++ b/src/main/java/net/minecraft/server/LightEngineThreaded.java
-@@ -0,0 +0,0 @@ import org.apache.logging.log4j.Logger;
+@@ -0,0 +0,0 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
- public class LightEngineThreaded extends LightEngine implements AutoCloseable {
  
      private static final Logger LOGGER = LogManager.getLogger();
--    private final ThreadedMailbox<Runnable> b;
+     private final ThreadedMailbox<Runnable> b;
 -    private final ObjectList<Pair<LightEngineThreaded.Update, Runnable>> c = new ObjectArrayList();
-+    private final ThreadedMailbox<Runnable> b; ThreadedMailbox<Runnable> mailbox; // Paper
+-    private final PlayerChunkMap d;
 +    // Paper start
 +    private static final int MAX_PRIORITIES = PlayerChunkMap.GOLDEN_TICKET + 2;
++    private final java.util.concurrent.ConcurrentLinkedQueue<Runnable> priorityChanges = new java.util.concurrent.ConcurrentLinkedQueue<>();
 +
 +    public void changePriority(long pair, int currentPriority, int priority) {
-+        this.mailbox.queue(() -> {
++        this.priorityChanges.add(() -> {
 +            ChunkLightQueue remove = this.queue.buckets[currentPriority].remove(pair);
 +            if (remove != null) {
 +                ChunkLightQueue existing = this.queue.buckets[priority].put(pair, remove);
@@ -1053,6 +1053,15 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        });
 +    }
 +
++    private boolean isChunkLightStatus(long pair) {
++        PlayerChunk playerChunk = playerChunkMap.getUpdatingChunk(pair);
++        if (playerChunk == null) {
++            return false;
++        }
++        ChunkStatus status = PlayerChunk.getChunkStatus(playerChunk.getTicketLevel());
++        return status != null && status.isAtLeastStatus(ChunkStatus.LIGHT);
++    }
++
 +    static class ChunkLightQueue {
 +        public boolean shouldFastUpdate;
 +        java.util.ArrayDeque<Runnable> pre = new java.util.ArrayDeque<Runnable>();
@@ -1063,7 +1072,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +
 +    // Retain the chunks priority level for queued light tasks
-+    private static class LightQueue {
++    private class LightQueue {
 +        private int size = 0;
 +        private int lowestPriority = MAX_PRIORITIES;
 +        private final it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap<ChunkLightQueue>[] buckets = new it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap[MAX_PRIORITIES];
@@ -1103,6 +1112,10 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        }
 +
 +        public boolean poll(java.util.List<Runnable> pre, java.util.List<Runnable> post) {
++            Runnable run;
++            while ((run = priorityChanges.poll()) != null) {
++                run.run();
++            }
 +            boolean hasWork = false;
 +            it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap<ChunkLightQueue>[] buckets = this.buckets;
 +            while (lowestPriority < MAX_PRIORITIES && !isEmpty()) {
@@ -1128,49 +1141,69 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +    private final LightQueue queue = new LightQueue();
 +    // Paper end
-     private final PlayerChunkMap d;
++    private final PlayerChunkMap d; private final PlayerChunkMap playerChunkMap; // Paper
      private final Mailbox<ChunkTaskQueueSorter.a<Runnable>> e;
      private volatile int f = 5;
-@@ -0,0 +0,0 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
+     private final AtomicBoolean g = new AtomicBoolean();
-         super(ilightaccess, true, flag);
-         this.d = playerchunkmap;
-         this.e = mailbox;
--        this.b = threadedmailbox;
-+        this.mailbox = this.b = threadedmailbox; // Paper
-     }
  
-     public void close() {}
+     public LightEngineThreaded(ILightAccess ilightaccess, PlayerChunkMap playerchunkmap, boolean flag, ThreadedMailbox<Runnable> threadedmailbox, Mailbox<ChunkTaskQueueSorter.a<Runnable>> mailbox) {
+         super(ilightaccess, true, flag);
+-        this.d = playerchunkmap;
++        this.d = playerchunkmap; this.playerChunkMap = d; // Paper
+         this.e = mailbox;
+         this.b = threadedmailbox;
+     }
 @@ -0,0 +0,0 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
  
      private void a(int i, int j, IntSupplier intsupplier, LightEngineThreaded.Update lightenginethreaded_update, Runnable runnable) {
          this.e.a(ChunkTaskQueueSorter.a(() -> {
 -            this.c.add(Pair.of(lightenginethreaded_update, runnable));
 -            if (this.c.size() >= this.f) {
+-                this.b();
+-            }
 +            // Paper start
 +            int priority = intsupplier.getAsInt();
-+            this.queue.add(ChunkCoordIntPair.pair(i, j), priority, lightenginethreaded_update, runnable); // Paper
++            this.queue.add(ChunkCoordIntPair.pair(i, j), priority, lightenginethreaded_update, runnable);
-+            if (priority <= 25) { // don't auto kick off unless priority
++            // Paper end
-+                // Paper end
-                 this.b();
-             }
  
+         }, ChunkCoordIntPair.pair(i, j), intsupplier));
+     }
 @@ -0,0 +0,0 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
+     public CompletableFuture<IChunkAccess> a(IChunkAccess ichunkaccess, boolean flag) {
          ChunkCoordIntPair chunkcoordintpair = ichunkaccess.getPos();
  
-         ichunkaccess.b(false);
+-        ichunkaccess.b(false);
 -        this.a(chunkcoordintpair.x, chunkcoordintpair.z, LightEngineThreaded.Update.PRE_UPDATE, SystemUtils.a(() -> {
 +        // Paper start
++        //ichunkaccess.b(false); // Don't need to disable this
 +        long pair = chunkcoordintpair.pair();
 +        CompletableFuture<IChunkAccess> future = new CompletableFuture<>();
-+        IntSupplier prioritySupplier = d.getPrioritySupplier(pair);
++        IntSupplier prioritySupplier = playerChunkMap.getPrioritySupplier(pair);
 +        this.e.a(ChunkTaskQueueSorter.a(() -> {
++            // Chunk's no longer needed
++            if (!isChunkLightStatus(pair)) {
++                this.d.c(chunkcoordintpair); // copied from end of method to release light ticket
++                future.complete(ichunkaccess);
++                return;
++            }
++            boolean[] skippedPre = {false};
 +            this.queue.add(pair, prioritySupplier.getAsInt(), LightEngineThreaded.Update.PRE_UPDATE, 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;
++                }
 +                // Paper end
              ChunkSection[] achunksection = ichunkaccess.getSections();
  
              for (int i = 0; i < 16; ++i) {
 @@ -0,0 +0,0 @@ public class LightEngineThreaded extends LightEngine implements AutoCloseable {
-             this.d.c(chunkcoordintpair);
+                 });
+             }
+ 
+-            this.d.c(chunkcoordintpair);
++            this.d.c(chunkcoordintpair); // Paper - if change, copy into !isChunkLightStatus above
          }, () -> {
              return "lightChunk " + chunkcoordintpair + " " + flag;
 +            // Paper start  - merge the 2 together
@@ -1178,6 +1211,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 -        return CompletableFuture.supplyAsync(() -> {
 +
 +        this.queue.add(pair, prioritySupplier.getAsInt(), LightEngineThreaded.Update.POST_UPDATE, () -> {
++            if (skippedPre[0]) return; // Paper - future's already complete
              ichunkaccess.b(true);
              super.b(chunkcoordintpair, false);
 -            return ichunkaccess;