From 463a09fd84f4d456094bbaf1608897879de235ff 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 87c0feb25..f3ab146d3 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -377,4 +377,15 @@ 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 344b95233..fcd9f5491 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() {
@@ -49,6 +50,7 @@ public class PlayerChunk {
         this.playerChunkMap = playerchunkmap;
         this.location = new ChunkCoordIntPair(i, j);
         this.chunk = playerchunkmap.getWorld().getChunkProviderServer().getOrLoadChunkAt(i, j);
+        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 9fd07f859..e29aaab2d 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 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
 }
-- 
2.18.0