From 38f954aac3cbf55ef4c2ab8a91559775e2dcc5c0 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 29cb718fb..695bdf2e6 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -393,4 +393,15 @@ 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 5497a458d..db43a8a9a 100644
--- a/src/main/java/net/minecraft/server/PlayerChunk.java
+++ b/src/main/java/net/minecraft/server/PlayerChunk.java
@@ -19,6 +19,7 @@ public class PlayerChunk {
     private int h;
     private long i;
     private boolean done;
+    boolean chunkExists; // Paper
 
     public PlayerChunk(PlayerChunkMap playerchunkmap, int ix, int j) {
         this.playerChunkMap = playerchunkmap;
@@ -26,6 +27,7 @@ public class PlayerChunk {
         ChunkProviderServer chunkproviderserver = playerchunkmap.getWorld().getChunkProvider();
         chunkproviderserver.a(ix, j);
         this.chunk = chunkproviderserver.getChunkAt(ix, j, true, false);
+        this.chunkExists = this.chunk != null || org.bukkit.craftbukkit.chunkio.ChunkIOExecutor.hasQueuedChunkLoad(playerChunkMap.getWorld(), ix, j); // Paper
         markChunkUsed(); // Paper - delay chunk unloads
     }
 
diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
index b1ece38b2..27343174d 100644
--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
@@ -136,6 +136,7 @@ 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();
@@ -145,6 +146,11 @@ 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 7ffb8f617..33d5fc7d5 100644
--- a/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java
+++ b/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java
@@ -34,4 +34,10 @@ 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
 }
-- 
2.20.0