From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Tue, 1 Mar 2016 23:09:29 -0600
Subject: [PATCH] Further improve server tick loop

Improves how the catchup buffer is handled, allowing it to roll both ways
increasing the effeciency of the thread sleep so it only will sleep once.

Also increases the buffer of the catchup to ensure server stays at 20 TPS unless extreme conditions

Previous implementation did not calculate TPS correctly.
Switch to a realistic rolling average and factor in std deviation as an extra reporting variable

diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index d3cd196e1a6f707ed5e0008123cc65df80422859..a7f9a3e57c7736b065b8dc4dba6e018ce73e5157 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -285,7 +285,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
     public org.bukkit.command.ConsoleCommandSender console;
     public org.bukkit.command.RemoteConsoleCommandSender remoteConsole;
     public ConsoleReader reader;
-    public static int currentTick = (int) (System.currentTimeMillis() / 50);
+    public static int currentTick = 0; // Paper - Further improve tick loop
     public java.util.Queue<Runnable> processQueue = new java.util.concurrent.ConcurrentLinkedQueue<Runnable>();
     public int autosavePeriod;
     public Commands vanillaCommandDispatcher;
@@ -294,7 +294,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
     // Spigot start
     public static final int TPS = 20;
     public static final int TICK_TIME = 1000000000 / MinecraftServer.TPS;
-    private static final int SAMPLE_INTERVAL = 100;
+    private static final int SAMPLE_INTERVAL = 20; // Paper
     public final double[] recentTps = new double[ 3 ];
     // Spigot end
     public final io.papermc.paper.configuration.PaperConfigurations paperConfigurations;
@@ -956,6 +956,57 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
     {
         return ( avg * exp ) + ( tps * ( 1 - exp ) );
     }
+
+    // Paper start - Further improve server tick loop
+    private static final long SEC_IN_NANO = 1000000000;
+    private static final long MAX_CATCHUP_BUFFER = TICK_TIME * TPS * 60L;
+    private long lastTick = 0;
+    private long catchupTime = 0;
+    public final RollingAverage tps1 = new RollingAverage(60);
+    public final RollingAverage tps5 = new RollingAverage(60 * 5);
+    public final RollingAverage tps15 = new RollingAverage(60 * 15);
+
+    public static class RollingAverage {
+        private final int size;
+        private long time;
+        private java.math.BigDecimal total;
+        private int index = 0;
+        private final java.math.BigDecimal[] samples;
+        private final long[] times;
+
+        RollingAverage(int size) {
+            this.size = size;
+            this.time = size * SEC_IN_NANO;
+            this.total = dec(TPS).multiply(dec(SEC_IN_NANO)).multiply(dec(size));
+            this.samples = new java.math.BigDecimal[size];
+            this.times = new long[size];
+            for (int i = 0; i < size; i++) {
+                this.samples[i] = dec(TPS);
+                this.times[i] = SEC_IN_NANO;
+            }
+        }
+
+        private static java.math.BigDecimal dec(long t) {
+            return new java.math.BigDecimal(t);
+        }
+        public void add(java.math.BigDecimal x, long t) {
+            time -= times[index];
+            total = total.subtract(samples[index].multiply(dec(times[index])));
+            samples[index] = x;
+            times[index] = t;
+            time += t;
+            total = total.add(x.multiply(dec(t)));
+            if (++index == size) {
+                index = 0;
+            }
+        }
+
+        public double getAverage() {
+            return total.divide(dec(time), 30, java.math.RoundingMode.HALF_UP).doubleValue();
+        }
+    }
+    private static final java.math.BigDecimal TPS_BASE = new java.math.BigDecimal(1E9).multiply(new java.math.BigDecimal(SAMPLE_INTERVAL));
+    // Paper End
     // Spigot End
 
     public static volatile RuntimeException chunkSystemCrash; // Paper - rewrite chunk system
@@ -972,7 +1023,8 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
 
             // Spigot start
             Arrays.fill( recentTps, 20 );
-            long curTime, tickSection = Util.getMillis(), tickCount = 1;
+            long start = System.nanoTime(), curTime, tickSection = start; // Paper - Further improve server tick loop
+            lastTick = start - TICK_TIME; // Paper
             while (this.running) {
                 // Paper start - rewrite chunk system
                 // guarantee that nothing can stop the server from halting if it can at least still tick
@@ -980,7 +1032,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
                     throw this.chunkSystemCrash;
                 }
                 // Paper end - rewrite chunk system
-                long i = (curTime = Util.getMillis()) - this.nextTickTime;
+                long i = ((curTime = System.nanoTime()) / (1000L * 1000L)) - this.nextTickTime; // Paper
 
                 if (i > 5000L && this.nextTickTime - this.lastOverloadWarning >= 30000L) { // CraftBukkit
                     long j = i / 50L;
@@ -992,12 +1044,18 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
                 }
 
                 ++MinecraftServer.currentTickLong; // Paper
-                if ( tickCount++ % MinecraftServer.SAMPLE_INTERVAL == 0 )
+                if ( ++MinecraftServer.currentTick % MinecraftServer.SAMPLE_INTERVAL == 0 )
                 {
-                    double currentTps = 1E3 / ( curTime - tickSection ) * MinecraftServer.SAMPLE_INTERVAL;
-                    this.recentTps[0] = MinecraftServer.calcTps( this.recentTps[0], 0.92, currentTps ); // 1/exp(5sec/1min)
-                    this.recentTps[1] = MinecraftServer.calcTps( this.recentTps[1], 0.9835, currentTps ); // 1/exp(5sec/5min)
-                    this.recentTps[2] = MinecraftServer.calcTps( this.recentTps[2], 0.9945, currentTps ); // 1/exp(5sec/15min)
+                    final long diff = curTime - tickSection;
+                    java.math.BigDecimal currentTps = TPS_BASE.divide(new java.math.BigDecimal(diff), 30, java.math.RoundingMode.HALF_UP);
+                    tps1.add(currentTps, diff);
+                    tps5.add(currentTps, diff);
+                    tps15.add(currentTps, diff);
+                    // Backwards compat with bad plugins
+                    this.recentTps[0] = tps1.getAverage();
+                    this.recentTps[1] = tps5.getAverage();
+                    this.recentTps[2] = tps15.getAverage();
+                    // Paper end
                     tickSection = curTime;
                 }
                 // Spigot end
@@ -1007,7 +1065,8 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
                     this.debugCommandProfiler = new MinecraftServer.TimeProfiler(Util.getNanos(), this.tickCount);
                 }
 
-                MinecraftServer.currentTick = (int) (System.currentTimeMillis() / 50); // CraftBukkit
+                //MinecraftServer.currentTick = (int) (System.currentTimeMillis() / 50); // CraftBukkit // Paper - don't overwrite current tick time
+                lastTick = curTime;
                 this.nextTickTime += 50L;
                 this.startMetricsRecordingTick();
                 this.profiler.push("tick");
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index fbc62e2b07a430dea8a827790bda5fbf6f19d05b..07536b696f734fb9e8d0abe1f414ae536610f9ce 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -2416,6 +2416,17 @@ public final class CraftServer implements Server {
         return CraftMagicNumbers.INSTANCE;
     }
 
+    // Paper - Add getTPS API - Further improve tick loop
+    @Override
+    public double[] getTPS() {
+        return new double[] {
+                net.minecraft.server.MinecraftServer.getServer().tps1.getAverage(),
+                net.minecraft.server.MinecraftServer.getServer().tps5.getAverage(),
+                net.minecraft.server.MinecraftServer.getServer().tps15.getAverage()
+        };
+    }
+    // Paper end
+
     // Spigot start
     private final org.bukkit.Server.Spigot spigot = new org.bukkit.Server.Spigot()
     {
diff --git a/src/main/java/org/spigotmc/TicksPerSecondCommand.java b/src/main/java/org/spigotmc/TicksPerSecondCommand.java
index 4ab81a99f906e3f28e026d0e50b5b943c1bdcfb5..b1a72aa3634405f3fce64c66677a75d8f77cb6f6 100644
--- a/src/main/java/org/spigotmc/TicksPerSecondCommand.java
+++ b/src/main/java/org/spigotmc/TicksPerSecondCommand.java
@@ -15,6 +15,12 @@ public class TicksPerSecondCommand extends Command
         this.usageMessage = "/tps";
         this.setPermission( "bukkit.command.tps" );
     }
+    // Paper start
+    private static final net.kyori.adventure.text.Component WARN_MSG = net.kyori.adventure.text.Component.text()
+        .append(net.kyori.adventure.text.Component.text("Warning: ", net.kyori.adventure.text.format.NamedTextColor.RED))
+        .append(net.kyori.adventure.text.Component.text("Memory usage on modern garbage collectors is not a stable value and it is perfectly normal to see it reach max. Please do not pay it much attention.", net.kyori.adventure.text.format.NamedTextColor.GOLD))
+        .build();
+    // Paper end
 
     @Override
     public boolean execute(CommandSender sender, String currentAlias, String[] args)
@@ -24,22 +30,33 @@ public class TicksPerSecondCommand extends Command
             return true;
         }
 
-        StringBuilder sb = new StringBuilder( ChatColor.GOLD + "TPS from last 1m, 5m, 15m: " );
-        for ( double tps : MinecraftServer.getServer().recentTps )
-        {
-            sb.append( this.format( tps ) );
-            sb.append( ", " );
+        // Paper start - Further improve tick handling
+        double[] tps = org.bukkit.Bukkit.getTPS();
+        String[] tpsAvg = new String[tps.length];
+
+        for ( int i = 0; i < tps.length; i++) {
+            tpsAvg[i] = TicksPerSecondCommand.format( tps[i] );
+        }
+        sender.sendMessage(net.kyori.adventure.text.Component.text("TPS from last 1m, 5m, 15m: " + org.apache.commons.lang.StringUtils.join(tpsAvg, ", "), net.kyori.adventure.text.format.NamedTextColor.GOLD));
+        if (args.length > 0 && args[0].equals("mem") && sender.hasPermission("bukkit.command.tpsmemory")) {
+            sender.sendMessage(net.kyori.adventure.text.Component.text()
+                .append(net.kyori.adventure.text.Component.text("Current Memory Usage: ", net.kyori.adventure.text.format.NamedTextColor.GOLD))
+                .append(net.kyori.adventure.text.Component.text(((Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory()) / (1024 * 1024)) + "/" + (Runtime.getRuntime().totalMemory() / (1024 * 1024)) + " mb (Max: " + (Runtime.getRuntime().maxMemory() / (1024 * 1024)) + " mb)", net.kyori.adventure.text.format.NamedTextColor.GREEN))
+            );
+            if (!this.hasShownMemoryWarning) {
+                sender.sendMessage(WARN_MSG);
+                this.hasShownMemoryWarning = true;
+            }
         }
-        sender.sendMessage( sb.substring( 0, sb.length() - 2 ) );
-        sender.sendMessage(ChatColor.GOLD + "Current Memory Usage: " + ChatColor.GREEN + ((Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory()) / (1024 * 1024)) + "/" + (Runtime.getRuntime().totalMemory() / (1024 * 1024)) + " mb (Max: "
-                + (Runtime.getRuntime().maxMemory() / (1024 * 1024)) + " mb)");
+        // Paper end
 
         return true;
     }
 
-    private String format(double tps)
+    private boolean hasShownMemoryWarning; // Paper
+    private static String format(double tps) // Paper - Made static
     {
         return ( ( tps > 18.0 ) ? ChatColor.GREEN : ( tps > 16.0 ) ? ChatColor.YELLOW : ChatColor.RED ).toString()
-                + ( ( tps > 20.0 ) ? "*" : "" ) + Math.min( Math.round( tps * 100.0 ) / 100.0, 20.0 );
+                + ( ( tps > 21.0 ) ? "*" : "" ) + Math.min( Math.round( tps * 100.0 ) / 100.0, 20.0 ); // Paper - only print * at 21, we commonly peak to 20.02 as the tick sleep is not accurate enough, stop the noise
     }
 }