Configurable Max Chunk Gens per Tick

Limit the number of generations that can occur in a single tick, forcing them
to be spread out more.

Defaulting to 10 as an average generation is going to be 3-6ms, which means 10 will
likely cause the server to lose TPS, but constrain how much.

This should result in no noticeable speed reduction in generation for servers not
lagging, and let larger servers reduce this value according to their own desires.

Spigot-Server-Patches/0261-Configurable-Max-Chunk-Gens-per-Tick.patch

@@ -0,0 +1,112 @@
+From db999c30b736d5e5f3317e9b5bd84007a99e1a75 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Mon, 1 Jan 2018 16:10:24 -0500
+Subject: [PATCH] Configurable Max Chunk Gens per Tick
+
+Limit the number of generations that can occur in a single tick, forcing them
+to be spread out more.
+
+Defaulting to 10 as an average generation is going to be 3-6ms, which means 10 will
+likely cause the server to lose TPS, but constrain how much.
+
+This should result in no noticeable speed reduction in generation for servers not
+lagging, and let larger servers reduce this value according to their own desires.
+
+diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+index e40ef515e..3d2cf635b 100644
+--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
++++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+@@ -467,4 +467,16 @@ public class PaperWorldConfig {
+         }
+         log("Max Chunk Sends Per Tick: " + maxChunkSendsPerTick);
+     }
++
++    public int maxChunkGensPerTick = 10;
++    private void maxChunkGensPerTick() {
++        maxChunkGensPerTick = getInt("max-chunk-gens-per-tick", maxChunkGensPerTick);
++        if (maxChunkGensPerTick <= 0) {
++            maxChunkSendsPerTick = Integer.MAX_VALUE;
++            log("Max Chunk Gens Per Tick: Unlimited (NOT RECOMMENDED)");
++        } else {
++            log("Max Chunk Gens Per Tick: " + maxChunkGensPerTick);
++        }
++    }
++
+ }
+diff --git a/src/main/java/net/minecraft/server/PlayerChunk.java b/src/main/java/net/minecraft/server/PlayerChunk.java
+index 045adbd3d..20e734bc8 100644
+--- a/src/main/java/net/minecraft/server/PlayerChunk.java
++++ b/src/main/java/net/minecraft/server/PlayerChunk.java
+@@ -27,6 +27,7 @@ public class PlayerChunk {
+     private boolean done;
+ 
+     // CraftBukkit start - add fields
++    boolean chunkExists; // Paper
+     private boolean loadInProgress = false;
+     private Runnable loadedRunnable = new Runnable() {
+         public void run() {
+@@ -50,6 +51,7 @@ public class PlayerChunk {
+         // CraftBukkit start
+         loadInProgress = true;
+         this.chunk = playerchunkmap.getWorld().getChunkProviderServer().getChunkAt(i, j, loadedRunnable, false);
++        this.chunkExists = this.chunk != null || ChunkIOExecutor.hasQueuedChunkLoad(playerChunkMap.getWorld(), i, j); // Paper
+         markChunkUsed(); // Paper - delay chunk unloads
+         // CraftBukkit end
+     }
+diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
+index 6ee9f6cfb..99652ae3e 100644
+--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
++++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
+@@ -166,6 +166,7 @@ public class PlayerChunkMap {
+             // Spigot start
+             org.spigotmc.SlackActivityAccountant activityAccountant = this.world.getMinecraftServer().slackActivityAccountant;
+             activityAccountant.startActivity(0.5);
++            int chunkGensAllowed = world.paperConfig.maxChunkGensPerTick; // Paper
+             // Spigot end
+ 
+             Iterator iterator1 = this.h.iterator();
+@@ -175,6 +176,11 @@ public class PlayerChunkMap {
+ 
+                 if (playerchunk1.f() == null) {
+                     boolean flag = playerchunk1.a(PlayerChunkMap.b);
++                    // Paper start
++                    if (flag && !playerchunk1.chunkExists && chunkGensAllowed-- <= 0) {
++                        continue;
++                    }
++                    // Paper end
+ 
+                     if (playerchunk1.a(flag)) {
+                         iterator1.remove();
+diff --git a/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java b/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java
+index 9aaca21a7..f50d55c8e 100644
+--- a/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java
++++ b/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java
+@@ -35,4 +35,10 @@ public class ChunkIOExecutor {
+     public static void tick() {
+         instance.finishActive();
+     }
++
++    // Paper start
++    public static boolean hasQueuedChunkLoad(World world, int x, int z) {
++        return instance.hasTask(new QueuedChunk(x, z, null, world, null));
++    }
++    // Paper end
+ }
+diff --git a/src/main/java/org/bukkit/craftbukkit/util/AsynchronousExecutor.java b/src/main/java/org/bukkit/craftbukkit/util/AsynchronousExecutor.java
+index 193c3621c..cf1258c55 100644
+--- a/src/main/java/org/bukkit/craftbukkit/util/AsynchronousExecutor.java
++++ b/src/main/java/org/bukkit/craftbukkit/util/AsynchronousExecutor.java
+@@ -351,4 +351,10 @@ public final class AsynchronousExecutor<P, T, C, E extends Throwable> {
+     public void setActiveThreads(final int coreSize) {
+         pool.setCorePoolSize(coreSize);
+     }
++
++    // Paper start
++    public boolean hasTask(P parameter) throws IllegalStateException {
++        return tasks.get(parameter) != null;
++    }
++    // Paper end
+ }
+-- 
+2.15.1
+