Load all already generated chunks via async chunk system

Currently we use the async chunk loading system only when players trigger
chunk loading. If a chunk is loaded for any other reason it goes through
a separate codepath. This means if a player has trigged a chunk load and
before the chunk loads something else wants the same chunk we will load it
twice and throw away the second result. With this change we instead use
the sync processing feature of the AsynchronousExecutor to load the chunk
which will pull it out of the queue if it was already queued to load. This
means we only ever load a chunk once. Because chunk generation is not
thread safe we still fallback to the vanilla chunk loading system if the
chunk does not currently exist.

By: Travis Watkins <amaranth@ubuntu.com>

paper-server/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java

@@ -5,7 +5,6 @@ import net.minecraft.server.ChunkProviderServer;
 import net.minecraft.server.ChunkRegionLoader;
 import net.minecraft.server.World;
 import org.bukkit.craftbukkit.util.AsynchronousExecutor;
-import org.bukkit.craftbukkit.util.LongHash;
 
 public class ChunkIOExecutor {
     static final int BASE_THREADS = 1;
@@ -13,12 +12,12 @@ public class ChunkIOExecutor {
 
     private static final AsynchronousExecutor<QueuedChunk, Chunk, Runnable, RuntimeException> instance = new AsynchronousExecutor<QueuedChunk, Chunk, Runnable, RuntimeException>(new ChunkIOProvider(), BASE_THREADS);
 
-    public static void waitForChunkLoad(World world, int x, int z) {
+    public static Chunk syncChunkLoad(World world, ChunkRegionLoader loader, ChunkProviderServer provider, int x, int z) {
-        instance.get(new QueuedChunk(LongHash.toLong(x, z), null, world, null));
+        return instance.getSkipQueue(new QueuedChunk(x, z, loader, world, provider));
     }
 
     public static void queueChunkLoad(World world, ChunkRegionLoader loader, ChunkProviderServer provider, int x, int z, Runnable runnable) {
-        instance.add(new QueuedChunk(LongHash.toLong(x, z), loader, world, provider), runnable);
+        instance.add(new QueuedChunk(x, z, loader, world, provider), runnable);
     }
 
     public static void adjustPoolSize(int players) {

paper-server/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOProvider.java

@@ -16,7 +16,7 @@ class ChunkIOProvider implements AsynchronousExecutor.CallBackProvider<QueuedChu
     // async stuff
     public Chunk callStage1(QueuedChunk queuedChunk) throws RuntimeException {
         ChunkRegionLoader loader = queuedChunk.loader;
-        Object[] data = loader.loadChunk(queuedChunk.world, LongHash.msw(queuedChunk.coords), LongHash.lsw(queuedChunk.coords));
+        Object[] data = loader.loadChunk(queuedChunk.world, queuedChunk.x, queuedChunk.z);
 
         if (data != null) {
             queuedChunk.compound = (NBTTagCompound) data[1];
@@ -30,27 +30,17 @@ class ChunkIOProvider implements AsynchronousExecutor.CallBackProvider<QueuedChu
     public void callStage2(QueuedChunk queuedChunk, Chunk chunk) throws RuntimeException {
         if(chunk == null) {
             // If the chunk loading failed just do it synchronously (may generate)
-            queuedChunk.provider.getChunkAt(LongHash.msw(queuedChunk.coords), LongHash.lsw(queuedChunk.coords));
+            queuedChunk.provider.originalGetChunkAt(queuedChunk.x, queuedChunk.z);
-            return;
-        }
-
-        int x = LongHash.msw(queuedChunk.coords);
-        int z = LongHash.lsw(queuedChunk.coords);
-
-        // See if someone already loaded this chunk while we were working on it (API, etc)
-        if (queuedChunk.provider.chunks.containsKey(queuedChunk.coords)) {
-            // Make sure it isn't queued for unload, we need it
-            queuedChunk.provider.unloadQueue.remove(queuedChunk.coords);
             return;
         }
 
         queuedChunk.loader.loadEntities(chunk, queuedChunk.compound.getCompound("Level"), queuedChunk.world);
         chunk.p = queuedChunk.provider.world.getTime();
-        queuedChunk.provider.chunks.put(queuedChunk.coords, chunk);
+        queuedChunk.provider.chunks.put(LongHash.toLong(queuedChunk.x, queuedChunk.z), chunk);
         chunk.addEntities();
 
         if (queuedChunk.provider.chunkProvider != null) {
-            queuedChunk.provider.chunkProvider.recreateStructures(x, z);
+            queuedChunk.provider.chunkProvider.recreateStructures(queuedChunk.x, queuedChunk.z);
         }
 
         Server server = queuedChunk.provider.world.getServer();
@@ -58,7 +48,7 @@ class ChunkIOProvider implements AsynchronousExecutor.CallBackProvider<QueuedChu
             server.getPluginManager().callEvent(new org.bukkit.event.world.ChunkLoadEvent(chunk.bukkitChunk, false));
         }
 
-        chunk.a(queuedChunk.provider, queuedChunk.provider, x, z);
+        chunk.a(queuedChunk.provider, queuedChunk.provider, queuedChunk.x, queuedChunk.z);
     }
 
     public void callStage3(QueuedChunk queuedChunk, Chunk chunk, Runnable runnable) throws RuntimeException {

paper-server/src/main/java/org/bukkit/craftbukkit/chunkio/QueuedChunk.java

@@ -6,14 +6,16 @@ import net.minecraft.server.NBTTagCompound;
 import net.minecraft.server.World;
 
 class QueuedChunk {
-    final long coords;
+    final int x;
+    final int z;
     final ChunkRegionLoader loader;
     final World world;
     final ChunkProviderServer provider;
     NBTTagCompound compound;
 
-    public QueuedChunk(long coords, ChunkRegionLoader loader, World world, ChunkProviderServer provider) {
+    public QueuedChunk(int x, int z, ChunkRegionLoader loader, World world, ChunkProviderServer provider) {
-        this.coords = coords;
+        this.x = x;
+        this.z = z;
         this.loader = loader;
         this.world = world;
         this.provider = provider;
@@ -21,14 +23,14 @@ class QueuedChunk {
 
     @Override
     public int hashCode() {
-        return (int) coords ^ world.hashCode();
+        return (x * 31 + z * 29) ^ world.hashCode();
     }
 
     @Override
     public boolean equals(Object object) {
         if (object instanceof QueuedChunk) {
             QueuedChunk other = (QueuedChunk) object;
-            return coords == other.coords && world == other.world;
+            return x == other.x && z == other.z && world == other.world;
         }
 
         return false;