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 dd104b1cd544983024ac60888940a1c0917d05a1..478dfe231720324e995dc4123fbf19b9ce26c16e 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -144,7 +144,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
     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 CommandDispatcher vanillaCommandDispatcher;
@@ -153,7 +153,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
     // Spigot start
     public static final int TPS = 20;
     public static final int TICK_TIME = 1000000000 / TPS;
-    private static final int SAMPLE_INTERVAL = 100;
+    private static final int SAMPLE_INTERVAL = 20; // Paper
     public final double[] recentTps = new double[ 3 ];
     public final SlackActivityAccountant slackActivityAccountant = new SlackActivityAccountant();
     // Spigot end
@@ -806,6 +806,57 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
     {
         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 w() {
@@ -818,30 +869,38 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
 
                 // Spigot start
                 Arrays.fill( recentTps, 20 );
-                long curTime, tickSection = SystemUtils.getMonotonicMillis(), tickCount = 1;
+                long start = System.nanoTime(), curTime, tickSection = start; // Paper - Further improve server tick loop
+                lastTick = start - TICK_TIME; // Paper
                 while (this.isRunning) {
-                    long i = (curTime = SystemUtils.getMonotonicMillis()) - this.nextTick;
+                    long i = ((curTime = System.nanoTime()) / (1000L * 1000L)) - this.nextTick; // Paper
 
                     if (i > 5000L && this.nextTick - this.lastOverloadTime >= 30000L) { // CraftBukkit
                         long j = i / 50L;
 
                         if (server.getWarnOnOverload()) // CraftBukkit
-                        MinecraftServer.LOGGER.warn("Can't keep up! Is the server overloaded? Running {}ms or {} ticks behind", i, j);
+                            MinecraftServer.LOGGER.warn("Can't keep up! Is the server overloaded? Running {}ms or {} ticks behind", i, j);
                         this.nextTick += j * 50L;
                         this.lastOverloadTime = this.nextTick;
                     }
 
-                    if ( tickCount++ % SAMPLE_INTERVAL == 0 )
+                    if ( ++MinecraftServer.currentTick % SAMPLE_INTERVAL == 0 )
                     {
-                        double currentTps = 1E3 / ( curTime - tickSection ) * SAMPLE_INTERVAL;
-                        recentTps[0] = calcTps( recentTps[0], 0.92, currentTps ); // 1/exp(5sec/1min)
-                        recentTps[1] = calcTps( recentTps[1], 0.9835, currentTps ); // 1/exp(5sec/5min)
-                        recentTps[2] = calcTps( 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
+                        recentTps[0] = tps1.getAverage();
+                        recentTps[1] = tps5.getAverage();
+                        recentTps[2] = tps15.getAverage();
+                        // Paper end
                         tickSection = curTime;
                     }
                     // Spigot end
 
-                    MinecraftServer.currentTick = (int) (System.currentTimeMillis() / 50); // CraftBukkit
+                    //MinecraftServer.currentTick = (int) (System.currentTimeMillis() / 50); // CraftBukkit // Paper - don't overwrite current tick time
+                    lastTick = curTime;
                     this.nextTick += 50L;
                     GameProfilerTick gameprofilertick = GameProfilerTick.a("Server");
 
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index 7a2409b78a044c37de1ee4fc772e4ac120ae657c..390714fa5822a61f64f6b3b8731397e9dae77cfd 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -2113,6 +2113,17 @@ 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 Spigot spigot = new Spigot()
     {
diff --git a/src/main/java/org/spigotmc/TicksPerSecondCommand.java b/src/main/java/org/spigotmc/TicksPerSecondCommand.java
index f5b6dec1cbe7501ce2ee9125920e810bc94670cc..e62890433ffbe0b4e48942fe6c38b599a19e58fd 100644
--- a/src/main/java/org/spigotmc/TicksPerSecondCommand.java
+++ b/src/main/java/org/spigotmc/TicksPerSecondCommand.java
@@ -24,22 +24,30 @@ 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( 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] = format( tps[i] );
+        }
+        sender.sendMessage(ChatColor.GOLD + "TPS from last 1m, 5m, 15m: " + org.apache.commons.lang.StringUtils.join(tpsAvg, ", "));
+        if (args.length > 0 && args[0].equals("mem") && sender.hasPermission("bukkit.command.tpsmemory")) {
+            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)");
+            if (!hasShownMemoryWarning) {
+                sender.sendMessage(ChatColor.RED + "Warning: " + ChatColor.GOLD + " 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.");
+                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
     }
 }