From 12a2b49cb2f955721aa6dfdb2edb2d04d5483426 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 8949b029..cd036b44 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -465,4 +465,16 @@ 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) {
+            maxChunkGensPerTick = 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 045adbd3..20e734bc 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 6ee9f6cf..99652ae3 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 9aaca21a..f50d55c8 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 193c3621..cf1258c5 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
 }
-- 
2.14.3