From 2e18115cc5205d7501d3cf894bcdb45f1f398f7f Mon Sep 17 00:00:00 2001
From: Geoff Crossland <gcrossland+bukkit@gmail.com>
Date: Thu, 26 Jan 2017 20:54:55 +0000
Subject: [PATCH] Replace chunk loading / unloading rate throttling.

Uses a scheme based on estimated tick slack time.
See https://hub.spigotmc.org/stash/projects/SPIGOT/repos/spigot/pull-requests/71/overview

diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index e6219e027..1db3cbbdd 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -185,6 +185,7 @@ import org.bukkit.event.server.ServerLoadEvent;
 // CraftBukkit end
 
 import org.bukkit.craftbukkit.SpigotTimings; // Spigot
+import org.spigotmc.SlackActivityAccountant; // Spigot
 
 public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTask> implements IMojangStatistics, ICommandListener, AutoCloseable {
 
@@ -295,6 +296,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
     public static final int TICK_TIME = 1000000000 / TPS;
     private static final int SAMPLE_INTERVAL = 100;
     public final double[] recentTps = new double[ 3 ];
+    public final SlackActivityAccountant slackActivityAccountant = new SlackActivityAccountant();
     // Spigot end
 
     public static <S extends MinecraftServer> S a(Function<Thread, S> function) {
@@ -1208,6 +1210,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
 
     public void a(BooleanSupplier booleansupplier) {
         SpigotTimings.serverTickTimer.startTiming(); // Spigot
+        this.slackActivityAccountant.tickStarted(); // Spigot
         long i = SystemUtils.getMonotonicNanos();
 
         ++this.tickCount;
@@ -1256,6 +1259,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
         this.frameTimer.a(i1 - i);
         this.profiler.exit();
         org.spigotmc.WatchdogThread.tick(); // Spigot
+        this.slackActivityAccountant.tickEnded(l); // Spigot
         SpigotTimings.serverTickTimer.stopTiming(); // Spigot
         org.spigotmc.CustomTimingsHandler.tick(); // Spigot
     }
diff --git a/src/main/java/net/minecraft/server/level/PlayerChunkMap.java b/src/main/java/net/minecraft/server/level/PlayerChunkMap.java
index d62dfd54f..bf599a89a 100644
--- a/src/main/java/net/minecraft/server/level/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/PlayerChunkMap.java
@@ -427,6 +427,9 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.e {
         }
 
     }
+
+    private static final double UNLOAD_QUEUE_RESIZE_FACTOR = 0.96; // Spigot
+
     protected void unloadChunks(BooleanSupplier booleansupplier) {
         GameProfilerFiller gameprofilerfiller = this.level.getMethodProfiler();
 
@@ -442,18 +445,28 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.e {
 
     private void b(BooleanSupplier booleansupplier) {
         LongIterator longiterator = this.toDrop.iterator();
-
-        for (int i = 0; longiterator.hasNext() && (booleansupplier.getAsBoolean() || i < 200 || this.toDrop.size() > 2000); longiterator.remove()) {
+        // Spigot start
+        org.spigotmc.SlackActivityAccountant activityAccountant = this.level.getMinecraftServer().slackActivityAccountant;
+        activityAccountant.startActivity(0.5);
+        int targetSize = (int) (this.toDrop.size() * UNLOAD_QUEUE_RESIZE_FACTOR);
+        // Spigot end
+        while (longiterator.hasNext()) { // Spigot
             long j = longiterator.nextLong();
+            longiterator.remove(); // Spigot
             PlayerChunk playerchunk = (PlayerChunk) this.updatingChunkMap.remove(j);
 
             if (playerchunk != null) {
                 this.pendingUnloads.put(j, playerchunk);
                 this.modified = true;
-                ++i;
+                // Spigot start
+                if (!booleansupplier.getAsBoolean() && this.toDrop.size() <= targetSize && activityAccountant.activityTimeIsExhausted()) {
+                    break;
+                }
+                // Spigot end
                 this.a(j, playerchunk);
             }
         }
+        activityAccountant.endActivity(); // Spigot
 
         Runnable runnable;
 
diff --git a/src/main/java/org/spigotmc/SlackActivityAccountant.java b/src/main/java/org/spigotmc/SlackActivityAccountant.java
new file mode 100644
index 000000000..aabc7ad20
--- /dev/null
+++ b/src/main/java/org/spigotmc/SlackActivityAccountant.java
@@ -0,0 +1,78 @@
+package org.spigotmc;
+
+/**
+ * Keeps track of the time spent doing main thread activities that can be spread across ticks,
+ * so that such work doesn't exceed the current tick's estimated available slack time. Each
+ * activity is allotted a proportion of the expected slack time according to its weight, versus the
+ * estimated total weight of all activities.
+ */
+public class SlackActivityAccountant {
+    private double prevTickSlackWeightReciprocal = 1 / MIN_SLACK_WEIGHT;
+    private static final double MIN_SLACK_WEIGHT = 1 / 65536.0;
+    private double averageTickNonSlackNanos = 0;
+    private static final double AVERAGING_FACTOR = 0.375;
+
+    private long currentActivityStartNanos;
+    private static final long OFF = -1;
+    private long currentActivityEndNanos;
+    private double tickSlackWeight;
+    private long tickSlackNanos;
+
+    private double getSlackFraction(double slackWeight) {
+        return Math.min(slackWeight * this.prevTickSlackWeightReciprocal, 1);
+    }
+
+    private int getEstimatedSlackNanos() {
+        return (int) Math.max(net.minecraft.server.MinecraftServer.TICK_TIME - (long) this.averageTickNonSlackNanos, 0);
+    }
+
+    public void tickStarted() {
+        this.currentActivityStartNanos = OFF;
+        this.tickSlackWeight = 0;
+        this.tickSlackNanos = 0;
+    }
+
+    public void startActivity(double slackWeight) {
+        double slackFraction0 = getSlackFraction(this.tickSlackWeight);
+        this.tickSlackWeight += slackWeight;
+        double slackFraction1 = getSlackFraction(this.tickSlackWeight);
+
+        long t = System.nanoTime();
+        this.currentActivityStartNanos = t;
+        this.currentActivityEndNanos = t + ((int) ((slackFraction1 - slackFraction0) * this.getEstimatedSlackNanos()));
+    }
+
+    private void endActivity(long endNanos) {
+        this.tickSlackNanos += endNanos - this.currentActivityStartNanos;
+        this.currentActivityStartNanos = OFF;
+    }
+
+    public boolean activityTimeIsExhausted() {
+        if (this.currentActivityStartNanos == OFF) {
+            return true;
+        }
+
+        long t = System.nanoTime();
+        if (t <= this.currentActivityEndNanos) {
+            return false;
+        } else {
+            this.endActivity(this.currentActivityEndNanos);
+            return true;
+        }
+    }
+
+    public void endActivity() {
+        if (this.currentActivityStartNanos == OFF) {
+            return;
+        }
+
+        this.endActivity(Math.min(System.nanoTime(), this.currentActivityEndNanos));
+    }
+
+    public void tickEnded(long tickNanos) {
+        this.prevTickSlackWeightReciprocal = 1 / Math.max(this.tickSlackWeight, MIN_SLACK_WEIGHT);
+
+        long tickNonSlackNanos = tickNanos - this.tickSlackNanos;
+        this.averageTickNonSlackNanos = this.averageTickNonSlackNanos * (1 - AVERAGING_FACTOR) + tickNonSlackNanos * AVERAGING_FACTOR;
+    }
+}
-- 
2.25.1