From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 18 Jun 2016 23:22:12 -0400
Subject: [PATCH] Delay Chunk Unloads based on Player Movement

When players are moving in the world, doing things such as building or exploring,
they will commonly go back and forth in a small area. This causes a ton of chunk load
and unload activity on the edge chunks of their view distance.

A simple back and forth movement in 6 blocks could spam a chunk to thrash a
loading and unload cycle over and over again.

This is very wasteful. This system introduces a delay of inactivity on a chunk
before it actually unloads, which will be handled by the ticket expiry process.

This allows servers with smaller worlds who do less long distance exploring to stop
wasting cpu cycles on saving/unloading/reloading chunks repeatedly.

diff --git a/src/main/java/net/minecraft/server/level/DistanceManager.java b/src/main/java/net/minecraft/server/level/DistanceManager.java
index 62118348d6fb00f063507debb488e1ff431d139c..9bc956068df3baabb9f8e02ee74a6397de2bf587 100644
--- a/src/main/java/net/minecraft/server/level/DistanceManager.java
+++ b/src/main/java/net/minecraft/server/level/DistanceManager.java
@@ -212,6 +212,27 @@ public abstract class DistanceManager {
         boolean removed = false; // CraftBukkit
         if (arraysetsorted.remove(ticket)) {
             removed = true; // CraftBukkit
+            // Paper start - delay chunk unloads for player tickets
+            long delayChunkUnloadsBy = chunkMap.level.paperConfig().chunks.delayChunkUnloadsBy.ticks();
+            if (ticket.getType() == TicketType.PLAYER && delayChunkUnloadsBy > 0) {
+                boolean hasPlayer = false;
+                for (Ticket<?> ticket1 : arraysetsorted) {
+                    if (ticket1.getType() == TicketType.PLAYER) {
+                        hasPlayer = true;
+                        break;
+                    }
+                }
+                ChunkHolder playerChunk = chunkMap.getUpdatingChunkIfPresent(i);
+                if (!hasPlayer && playerChunk != null && playerChunk.isFullChunkReady()) {
+                    Ticket<Long> delayUnload = new Ticket<Long>(TicketType.DELAY_UNLOAD, 33, i);
+                    delayUnload.delayUnloadBy = delayChunkUnloadsBy;
+                    delayUnload.setCreatedTick(this.ticketTickCounter);
+                    arraysetsorted.remove(delayUnload);
+                    // refresh ticket
+                    arraysetsorted.add(delayUnload);
+                }
+            }
+            // Paper end
         }
 
         if (arraysetsorted.isEmpty()) {
diff --git a/src/main/java/net/minecraft/server/level/Ticket.java b/src/main/java/net/minecraft/server/level/Ticket.java
index ffc43e5d3d0563c9e9c171064511b2c65ddf67e1..f1128f0d4a9a0241ac6c9bc18dd13b431c616bb1 100644
--- a/src/main/java/net/minecraft/server/level/Ticket.java
+++ b/src/main/java/net/minecraft/server/level/Ticket.java
@@ -7,11 +7,13 @@ public final class Ticket<T> implements Comparable<Ticket<?>> {
     private final int ticketLevel;
     public final T key;
     public long createdTick;
+    public long delayUnloadBy; // Paper
 
     protected Ticket(TicketType<T> type, int level, T argument) {
         this.type = type;
         this.ticketLevel = level;
         this.key = argument;
+        this.delayUnloadBy = type.timeout; // Paper
     }
 
     @Override
@@ -60,7 +62,7 @@ public final class Ticket<T> implements Comparable<Ticket<?>> {
     }
 
     protected boolean timedOut(long currentTick) {
-        long l = this.type.timeout();
+        long l = delayUnloadBy; // Paper
         return l != 0L && currentTick - this.createdTick > l;
     }
 }
diff --git a/src/main/java/net/minecraft/server/level/TicketType.java b/src/main/java/net/minecraft/server/level/TicketType.java
index 78fbb4c3e52e900956ae0811aaf934c81ee5ea48..8770fe0db46b01e8b608637df4f1a669a3f4cdde 100644
--- a/src/main/java/net/minecraft/server/level/TicketType.java
+++ b/src/main/java/net/minecraft/server/level/TicketType.java
@@ -28,6 +28,7 @@ public class TicketType<T> {
     public static final TicketType<ChunkPos> UNKNOWN = TicketType.create("unknown", Comparator.comparingLong(ChunkPos::toLong), 1);
     public static final TicketType<Unit> PLUGIN = TicketType.create("plugin", (a, b) -> 0); // CraftBukkit
     public static final TicketType<org.bukkit.plugin.Plugin> PLUGIN_TICKET = TicketType.create("plugin_ticket", (plugin1, plugin2) -> plugin1.getClass().getName().compareTo(plugin2.getClass().getName())); // CraftBukkit
+    public static final TicketType<Long> DELAY_UNLOAD = create("delay_unload", Long::compareTo, 300); // Paper
 
     public static <T> TicketType<T> create(String name, Comparator<T> argumentComparator) {
         return new TicketType<>(name, argumentComparator, 0L);