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 0746932a3191669052f15270f5c94efbce0bd0c2..0f4fca90fd6c3788a5762c96c344899cb1665466 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -639,4 +639,13 @@ 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/ChunkMapDistance.java b/src/main/java/net/minecraft/server/ChunkMapDistance.java
index 4c4108705e9d25912e57a7b3c28b4f1abad58377..893c0085bca0a8d77a85dba1cc29f2dec96c56ec 100644
--- a/src/main/java/net/minecraft/server/ChunkMapDistance.java
+++ b/src/main/java/net/minecraft/server/ChunkMapDistance.java
@@ -176,6 +176,27 @@ 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/Ticket.java b/src/main/java/net/minecraft/server/Ticket.java
index b5030d6f5d917ba33fb3c40903384fa7a56bc5f1..e41cb8613efc86499dfe3be36c9130ab6dc9b89e 100644
--- a/src/main/java/net/minecraft/server/Ticket.java
+++ b/src/main/java/net/minecraft/server/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/TicketType.java b/src/main/java/net/minecraft/server/TicketType.java
index 6fd852db6bcfbfbf84ec2acf6d23b08a6051165c..5c789b25f1df2eae8ea8ceb4ba977ba336fe6d5e 100644
--- a/src/main/java/net/minecraft/server/TicketType.java
+++ b/src/main/java/net/minecraft/server/TicketType.java
@@ -26,6 +26,7 @@ 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);