From 4ea0d21a910e0b43daefd58d3f4c477d9ca703fa 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 af69342e6c..ca7efc9175 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -388,4 +388,15 @@ 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 abf5a7554d..84896d6f6b 100644
--- a/src/main/java/net/minecraft/server/PlayerChunk.java
+++ b/src/main/java/net/minecraft/server/PlayerChunk.java
@@ -28,6 +28,7 @@ public class PlayerChunk {
     // CraftBukkit start - add fields
     // You know the drill, https://hub.spigotmc.org/stash/projects/SPIGOT/repos/craftbukkit/browse
     // All may seem good at first, but there's deeper issues if you play for a bit
+    boolean chunkExists; // Paper
     private boolean loadInProgress = false;
     private Runnable loadedRunnable = new Runnable() {
         public void run() {
@@ -58,6 +59,7 @@ public class PlayerChunk {
 
         chunkproviderserver.a(i, j);
         this.chunk = chunkproviderserver.getChunkAt(i, j, true, false);
+        this.chunkExists = this.chunk != null || ChunkIOExecutor.hasQueuedChunkLoad(playerChunkMap.getWorld(), i, 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 54f31349e9..d1a443ca8d 100644
--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
@@ -140,6 +140,7 @@ 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();
@@ -149,6 +150,11 @@ 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 7ffb8f6172..33d5fc7d5e 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 193c3621c6..cf1258c559 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
 }
-- 
2.19.0