--- a/net/minecraft/server/level/ServerChunkCache.java
+++ b/net/minecraft/server/level/ServerChunkCache.java
@@ -83,6 +83,16 @@
         this.clearCache();
     }
 
+    // CraftBukkit start - properly implement isChunkLoaded
+    public boolean isChunkLoaded(int chunkX, int chunkZ) {
+        ChunkHolder chunk = this.chunkMap.getUpdatingChunkIfPresent(ChunkPos.asLong(chunkX, chunkZ));
+        if (chunk == null) {
+            return false;
+        }
+        return chunk.getFullChunkNow() != null;
+    }
+    // CraftBukkit end
+
     @Override
     @Override
     public ThreadedLevelLightEngine getLightEngine() {
@@ -127,10 +135,10 @@
             ChunkAccess chunkaccess;
 
             for (int l = 0; l < 4; ++l) {
-                if (k == this.lastChunkPos[l] && chunkstatus == this.lastChunkStatus[l]) {
-                    chunkaccess = this.lastChunk[l];
-                    if (chunkaccess != null || !flag) {
-                        return chunkaccess;
+                if (k == this.lastChunkPos[l] && requiredStatus == this.lastChunkStatus[l]) {
+                    ichunkaccess = this.lastChunk[l];
+                    if (ichunkaccess != null) { // CraftBukkit - the chunk can become accessible in the meantime TODO for non-null chunks it might also make sense to check that the chunk's state hasn't changed in the meantime
+                        return ichunkaccess;
                     }
                 }
             }
@@ -231,10 +238,18 @@
         int l = ChunkLevel.byStatus(chunkstatus);
         ChunkHolder chunkholder = this.getVisibleChunkIfPresent(k);
 
-        if (flag) {
-            this.distanceManager.addTicket(TicketType.UNKNOWN, chunkpos, l, chunkpos);
-            if (this.chunkAbsent(chunkholder, l)) {
-                ProfilerFiller profilerfiller = this.level.getProfiler();
+        // CraftBukkit start - don't add new ticket for currently unloading chunk
+        boolean currentlyUnloading = false;
+        if (playerchunk != null) {
+            FullChunkStatus oldChunkState = ChunkLevel.fullStatus(playerchunk.oldTicketLevel);
+            FullChunkStatus currentChunkState = ChunkLevel.fullStatus(playerchunk.getTicketLevel());
+            currentlyUnloading = (oldChunkState.isOrAfter(FullChunkStatus.FULL) && !currentChunkState.isOrAfter(FullChunkStatus.FULL));
+        }
+        if (load && !currentlyUnloading) {
+            // CraftBukkit end
+            this.distanceManager.addTicket(TicketType.UNKNOWN, chunkcoordintpair, l, chunkcoordintpair);
+            if (this.chunkAbsent(playerchunk, l)) {
+                ProfilerFiller gameprofilerfiller = this.level.getProfiler();
 
                 profilerfiller.push("chunkLoad");
                 this.runDistanceManagerUpdates();
@@ -249,8 +264,8 @@
         return this.chunkAbsent(chunkholder, l) ? ChunkHolder.UNLOADED_CHUNK_FUTURE : chunkholder.getOrScheduleFuture(chunkstatus, this.chunkMap);
     }
 
-    private boolean chunkAbsent(@Nullable ChunkHolder chunkholder, int i) {
-        return chunkholder == null || chunkholder.getTicketLevel() > i;
+    private boolean chunkAbsent(@Nullable ChunkHolder chunkHolder, int status) {
+        return chunkHolder == null || chunkHolder.oldTicketLevel > status; // CraftBukkit using oldTicketLevel for isLoaded checks
     }
 
     @Override
@@ -335,11 +346,31 @@
     @Override
     @Override
     public void close() throws IOException {
-        this.save(true);
+        // CraftBukkit start
+        close(true);
+    }
+
+    public void close(boolean save) throws IOException {
+        if (save) {
+            this.save(true);
+        }
+        // CraftBukkit end
         this.lightEngine.close();
         this.chunkMap.close();
     }
 
+    // CraftBukkit start - modelled on below
+    public void purgeUnload() {
+        this.level.getProfiler().push("purge");
+        this.distanceManager.purgeStaleTickets();
+        this.runDistanceManagerUpdates();
+        this.level.getProfiler().popPush("unload");
+        this.chunkMap.tick(() -> true);
+        this.level.getProfiler().pop();
+        this.clearCache();
+    }
+    // CraftBukkit end
+
     @Override
     @Override
     public void tick(BooleanSupplier booleansupplier, boolean flag) {
@@ -385,13 +415,13 @@
                 int k = this.distanceManager.getNaturalSpawnChunkCount();
                 NaturalSpawner.SpawnState naturalspawner_spawnstate = NaturalSpawner.createState(k, this.level.getAllEntities(), this::getFullChunk, new LocalMobCapCalculator(this.chunkMap));
 
-                this.lastSpawnState = naturalspawner_spawnstate;
-                profilerfiller.popPush("spawnAndTick");
-                boolean flag = this.level.getGameRules().getBoolean(GameRules.RULE_DOMOBSPAWNING);
+                this.lastSpawnState = spawnercreature_d;
+                gameprofilerfiller.popPush("spawnAndTick");
+                boolean flag = this.level.getGameRules().getBoolean(GameRules.RULE_DOMOBSPAWNING) && !this.level.players().isEmpty(); // CraftBukkit
 
                 Util.shuffle(list, this.level.random);
                 int l = this.level.getGameRules().getInt(GameRules.RULE_RANDOMTICKING);
-                boolean flag1 = this.level.getLevelData().getGameTime() % 400L == 0L;
+                boolean flag1 = this.level.ticksPerSpawnCategory.getLong(org.bukkit.entity.SpawnCategory.ANIMAL) != 0L && this.level.getLevelData().getGameTime() % this.level.ticksPerSpawnCategory.getLong(org.bukkit.entity.SpawnCategory.ANIMAL) == 0L; // CraftBukkit
                 Iterator iterator1 = list.iterator();
 
                 while (iterator1.hasNext()) {
@@ -604,7 +624,9 @@
         }
 
         @Override
-        protected boolean pollTask() {
+        // CraftBukkit start - process pending Chunk loadCallback() and unloadCallback() after each run task
+        public boolean pollTask() {
+        try {
             if (ServerChunkCache.this.runDistanceManagerUpdates()) {
                 return true;
             } else {
@@ -612,6 +636,8 @@
                 return super.pollTask();
             }
         }
+        // CraftBukkit end
+        }
     }
 
     private static record ChunkAndHolder(LevelChunk chunk, ChunkHolder holder) {