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/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index 6463d3e4837d032a35654a035f42b8a805e0e286..1655bca0502e7b871de4addaa163536d86547a02 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -637,4 +637,13 @@ public class PaperWorldConfig {
     private void viewDistance() {
         this.noTickViewDistance = this.getInt("viewdistances.no-tick-view-distance", -1);
     }
+
+    public long delayChunkUnloadsBy;
+    private void delayChunkUnloadsBy() {
+        delayChunkUnloadsBy = PaperConfig.getSeconds(getString("delay-chunk-unloads-by", "10s"));
+        if (delayChunkUnloadsBy > 0) {
+            log("Delaying chunk unloads by " + delayChunkUnloadsBy + " seconds");
+            delayChunkUnloadsBy *= 20;
+        }
+    }
 }
diff --git a/src/main/java/net/minecraft/server/level/ChunkMapDistance.java b/src/main/java/net/minecraft/server/level/ChunkMapDistance.java
index a3c44fdfca8290313b9b1117b984533183b583ad..3644e8b24b082e17752ef52934625416130aaa08 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMapDistance.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMapDistance.java
@@ -185,6 +185,27 @@ public abstract class ChunkMapDistance {
         boolean removed = false; // CraftBukkit
         if (arraysetsorted.remove(ticket)) {
             removed = true; // CraftBukkit
+            // Paper start - delay chunk unloads for player tickets
+            long delayChunkUnloadsBy = chunkMap.world.paperConfig.delayChunkUnloadsBy;
+            if (ticket.getTicketType() == TicketType.PLAYER && delayChunkUnloadsBy > 0) {
+                boolean hasPlayer = false;
+                for (Ticket<?> ticket1 : arraysetsorted) {
+                    if (ticket1.getTicketType() == TicketType.PLAYER) {
+                        hasPlayer = true;
+                        break;
+                    }
+                }
+                PlayerChunk playerChunk = chunkMap.getUpdatingChunk(i);
+                if (!hasPlayer && playerChunk != null && playerChunk.isFullChunkReady()) {
+                    Ticket<Long> delayUnload = new Ticket<Long>(TicketType.DELAY_UNLOAD, 33, i);
+                    delayUnload.delayUnloadBy = delayChunkUnloadsBy;
+                    delayUnload.setCurrentTick(this.currentTick);
+                    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 90cbd12611b7b078f35f08f910453bcc02f6665b..6e5ae954c6eb40590bf8c83f592c22088d489be8 100644
--- a/src/main/java/net/minecraft/server/level/Ticket.java
+++ b/src/main/java/net/minecraft/server/level/Ticket.java
@@ -9,11 +9,13 @@ public final class Ticket<T> implements Comparable<Ticket<?>> {
     public final T identifier; public final T getObjectReason() { return this.identifier; } // Paper - OBFHELPER
     private long d; public final long getCreationTick() { return this.d; } // Paper - OBFHELPER
     public int priority = 0; // Paper
+    public long delayUnloadBy; // Paper
 
     protected Ticket(TicketType<T> tickettype, int i, T t0) {
         this.a = tickettype;
         this.b = i;
         this.identifier = t0;
+        this.delayUnloadBy = tickettype.loadPeriod; // Paper
     }
 
     public int compareTo(Ticket<?> ticket) {
@@ -63,7 +65,7 @@ public final class Ticket<T> implements Comparable<Ticket<?>> {
     }
 
     protected boolean b(long i) {
-        long j = this.a.b();
+        long j = delayUnloadBy; // Paper
 
         return j != 0L && i - this.d > j;
     }
diff --git a/src/main/java/net/minecraft/server/level/TicketType.java b/src/main/java/net/minecraft/server/level/TicketType.java
index f5d18834e0e2ee0e3bcf55810456766d2f134450..3c804c7b20a14ea6e510810e2be10c1cc89ff5c1 100644
--- a/src/main/java/net/minecraft/server/level/TicketType.java
+++ b/src/main/java/net/minecraft/server/level/TicketType.java
@@ -30,6 +30,7 @@ public class TicketType<T> {
     public static final TicketType<Long> ASYNC_LOAD = a("async_load", Long::compareTo); // Paper
     public static final TicketType<ChunkCoordIntPair> PRIORITY = a("priority", Comparator.comparingLong(ChunkCoordIntPair::pair), 300); // Paper
     public static final TicketType<ChunkCoordIntPair> URGENT = a("urgent", Comparator.comparingLong(ChunkCoordIntPair::pair), 300); // Paper
+    public static final TicketType<Long> DELAY_UNLOAD = a("delay_unload", Long::compareTo, 300); // Paper
 
     public static <T> TicketType<T> a(String s, Comparator<T> comparator) {
         return new TicketType<>(s, comparator, 0L);