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 d76dae9ce9022308b316080ac48b7030d674cc6b..e9d56d75b7c648f04d3a56942b2866090c570129 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -296,7 +296,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
     public org.bukkit.craftbukkit.CraftServer server;
     public OptionSet options;
     public org.bukkit.command.ConsoleCommandSender console;
-    public static int currentTick = (int) (System.currentTimeMillis() / 50);
+    public static int currentTick; // Paper - improve tick loop
     public java.util.Queue<Runnable> processQueue = new java.util.concurrent.ConcurrentLinkedQueue<Runnable>();
     public int autosavePeriod;
     public Commands vanillaCommandDispatcher;
@@ -305,7 +305,8 @@ 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 - improve server tick loop
+    @Deprecated(forRemoval = true) // Paper
     public final double[] recentTps = new double[ 3 ];
     // Spigot end
     public final io.papermc.paper.configuration.PaperConfigurations paperConfigurations; // Paper - add paper configuration files
@@ -1020,6 +1021,57 @@ 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
 
     protected void runServer() {
@@ -1034,7 +1086,10 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
 
             // Spigot start
             Arrays.fill( this.recentTps, 20 );
-            long tickSection = Util.getMillis(), tickCount = 1;
+            // Paper start - further improve server tick loop
+            long tickSection = Util.getNanos();
+            long currentTime;
+            // Paper end - further improve server tick loop
             while (this.running) {
                 long i;
 
@@ -1057,15 +1112,22 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
                 }
                 // Spigot start
                 ++MinecraftServer.currentTickLong; // Paper - track current tick as a long
-                if ( tickCount++ % MinecraftServer.SAMPLE_INTERVAL == 0 )
-                {
-                    long curTime = Util.getMillis();
-                    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)
-                    tickSection = curTime;
+                // Paper start - further improve server tick loop
+                currentTime = Util.getNanos();
+                if (++MinecraftServer.currentTick % MinecraftServer.SAMPLE_INTERVAL == 0) {
+                    final long diff = currentTime - tickSection;
+                    final 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();
+                    tickSection = currentTime;
                 }
+                // Paper end - further improve server tick loop
                 // Spigot end
 
                 boolean flag = i == 0L;
@@ -1075,7 +1137,8 @@ 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 = currentTime;
                 this.nextTickTimeNanos += i;
                 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 f2355612b497079f1de84e953c36720794da51d8..1056badff06575ef13907afac60af734ffa2b863 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -2673,7 +2673,11 @@ public final class CraftServer implements Server {
 
     @Override
     public double[] getTPS() {
-        return new double[]{0, 0, 0}; // TODO
+        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 start - adventure sounds
diff --git a/src/main/java/org/spigotmc/TicksPerSecondCommand.java b/src/main/java/org/spigotmc/TicksPerSecondCommand.java
index d9ec48be0fdd2bfea938aa29e36b0f6ffa839ab2..9eb2823cc8f83bad2626fc77578b0162d9ed5782 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 +30,40 @@ 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();
+        net.kyori.adventure.text.Component[] tpsAvg = new net.kyori.adventure.text.Component[tps.length];
+
+        for ( int i = 0; i < tps.length; i++) {
+            tpsAvg[i] = TicksPerSecondCommand.format( tps[i] );
+        }
+
+        net.kyori.adventure.text.TextComponent.Builder builder = net.kyori.adventure.text.Component.text();
+        builder.append(net.kyori.adventure.text.Component.text("TPS from last 1m, 5m, 15m: ", net.kyori.adventure.text.format.NamedTextColor.GOLD));
+        builder.append(net.kyori.adventure.text.Component.join(net.kyori.adventure.text.JoinConfiguration.commas(true), tpsAvg));
+        sender.sendMessage(builder.asComponent());
+        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 net.kyori.adventure.text.Component 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 );
+        // Paper
+        net.kyori.adventure.text.format.TextColor color = ( ( tps > 18.0 ) ? net.kyori.adventure.text.format.NamedTextColor.GREEN : ( tps > 16.0 ) ? net.kyori.adventure.text.format.NamedTextColor.YELLOW : net.kyori.adventure.text.format.NamedTextColor.RED );
+        String amount = Math.min(Math.round(tps * 100.0) / 100.0, 20.0) + (tps > 21.0  ? "*" : ""); // Paper - only print * at 21, we commonly peak to 20.02 as the tick sleep is not accurate enough, stop the noise
+        return net.kyori.adventure.text.Component.text(amount, color);
+        // Paper end
     }
 }