From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Thu, 9 Apr 2020 00:09:26 -0400
Subject: [PATCH] Mid Tick Chunk Tasks - Speed up processing of chunk loads and
 generation

Credit to Spotted for the idea

A lot of the new chunk system requires constant back and forth the main thread
to handle priority scheduling and ensuring conflicting tasks do not run at the
same time.

The issue is, these queues are only checked at either:

A) Sync Chunk Loads
B) End of Tick while sleeping

This results in generating chunks sitting waiting for a full tick to
complete before it will even start the next unit of work to do.

Additionally, this also delays loading of chunks until this same timing.

We will now periodically poll the chunk task queues throughout the tick,
looking for work to do.
We do this in a fair method that considers all worlds, not just the one being
ticked, so that each world can get 1 task procesed each before the next pass.

In a view distance of 15, chunk loading performance was visually faster on the client.

Flying at high speed in spectator mode was able to keep up with chunk loading (as long as they are already generated)

diff --git a/src/main/java/co/aikar/timings/MinecraftTimings.java b/src/main/java/co/aikar/timings/MinecraftTimings.java
index a58ef60d9976b3afc50e94364cf474bd2e5fdfd6..dd07223978c9aa648673d96ba7b3db1160d43bbf 100644
--- a/src/main/java/co/aikar/timings/MinecraftTimings.java
+++ b/src/main/java/co/aikar/timings/MinecraftTimings.java
@@ -13,6 +13,7 @@ import java.util.Map;
 public final class MinecraftTimings {
 
     public static final Timing serverOversleep = Timings.ofSafe("Server Oversleep");
+    public static final Timing midTickChunkTasks = Timings.ofSafe("Mid Tick Chunk Tasks");
     public static final Timing playerListTimer = Timings.ofSafe("Player List");
     public static final Timing commandFunctionsTimer = Timings.ofSafe("Command Functions");
     public static final Timing connectionTimer = Timings.ofSafe("Connection Handler");
diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
index 8508b3e10e60a4ce36d471b1d3f7ffc836a6ddf7..aad1420dc63c16b558ad1ca34accf8a7a9af6363 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -405,4 +405,9 @@ public class PaperConfig {
             log("Async Chunks: Enabled - Chunks will be loaded much faster, without lag.");
         }
     }
+
+    public static int midTickChunkTasks = 1000;
+    private static void midTickChunkTasks() {
+        midTickChunkTasks = getInt("settings.chunk-tasks-per-tick", midTickChunkTasks);
+    }
 }
diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
index e14e8bcf235339c1537a1e0a7702a364ee784c93..d1f832db33f21f8ba910d2c0c163af78718d298f 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -694,6 +694,7 @@ public class ChunkProviderServer extends IChunkProvider {
         this.world.getMethodProfiler().enter("purge");
         this.world.timings.doChunkMap.startTiming(); // Spigot
         this.chunkMapDistance.purgeTickets();
+        this.world.getMinecraftServer().midTickLoadChunks(); // Paper
         this.tickDistanceManager();
         this.world.timings.doChunkMap.stopTiming(); // Spigot
         this.world.getMethodProfiler().exitEnter("chunks");
@@ -703,6 +704,7 @@ public class ChunkProviderServer extends IChunkProvider {
         this.world.timings.doChunkUnload.startTiming(); // Spigot
         this.world.getMethodProfiler().exitEnter("unload");
         this.playerChunkMap.unloadChunks(booleansupplier);
+        this.world.getMinecraftServer().midTickLoadChunks(); // Paper
         this.world.timings.doChunkUnload.stopTiming(); // Spigot
         this.world.getMethodProfiler().exit();
         this.clearCache();
@@ -756,7 +758,7 @@ public class ChunkProviderServer extends IChunkProvider {
                 entityPlayer.playerNaturallySpawnedEvent.callEvent();
             };
             // Paper end
-            this.playerChunkMap.forEachVisibleChunk((playerchunk) -> { // Paper - safe iterator incase chunk loads, also no wrapping
+            final int[] chunksTicked = {0}; this.playerChunkMap.forEachVisibleChunk((playerchunk) -> { // Paper - safe iterator incase chunk loads, also no wrapping
                 Optional<Chunk> optional = ((Either) playerchunk.a().getNow(PlayerChunk.UNLOADED_CHUNK)).left();
 
                 if (optional.isPresent()) {
@@ -780,6 +782,7 @@ public class ChunkProviderServer extends IChunkProvider {
                             this.world.timings.chunkTicks.startTiming(); // Spigot // Paper
                             this.world.a(chunk, k);
                             this.world.timings.chunkTicks.stopTiming(); // Spigot // Paper
+                            if (chunksTicked[0]++ % 10 == 0) this.world.getMinecraftServer().midTickLoadChunks(); // Paper
                         }
                     }
                 }
@@ -936,6 +939,41 @@ public class ChunkProviderServer extends IChunkProvider {
             super.executeTask(runnable);
         }
 
+        // Paper start
+        private long lastMidTickChunkTask = 0;
+        public boolean pollChunkLoadTasks() {
+            if (com.destroystokyo.paper.io.chunk.ChunkTaskManager.pollChunkWaitQueue() || ChunkProviderServer.this.world.asyncChunkTaskManager.pollNextChunkTask()) {
+                try {
+                    ChunkProviderServer.this.tickDistanceManager();
+                } finally {
+                    // from below: process pending Chunk loadCallback() and unloadCallback() after each run task
+                    playerChunkMap.callbackExecutor.run();
+                }
+                return true;
+            }
+            return false;
+        }
+        public void midTickLoadChunks() {
+            MinecraftServer server = ChunkProviderServer.this.world.getMinecraftServer();
+            // always try to load chunks, restrain generation/other updates only. don't count these towards tick count
+            //noinspection StatementWithEmptyBody
+            while (pollChunkLoadTasks()) {}
+
+            if (System.nanoTime() - lastMidTickChunkTask < 200000) {
+                return;
+            }
+
+            for (;server.midTickChunksTasksRan < com.destroystokyo.paper.PaperConfig.midTickChunkTasks && server.canSleepForTick();) {
+                if (this.executeNext()) {
+                    server.midTickChunksTasksRan++;
+                    lastMidTickChunkTask = System.nanoTime();
+                } else {
+                    break;
+                }
+            }
+        }
+        // Paper end
+
         @Override
         protected boolean executeNext() {
         // CraftBukkit start - process pending Chunk loadCallback() and unloadCallback() after each run task
diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index 962061aa4de1cad05acac4fe09ecedbb81c55d9b..9e68d293ab8d67e9450a6633beccfba881d2287a 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -942,6 +942,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
                         // Paper end
                         tickSection = curTime;
                     }
+                    midTickChunksTasksRan = 0; // Paper
                     // Spigot end
 
                     //MinecraftServer.currentTick = (int) (System.currentTimeMillis() / 50); // CraftBukkit // Paper - don't overwrite current tick time
@@ -1011,7 +1012,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
 
     }
 
-    private boolean canSleepForTick() {
+    public boolean canSleepForTick() { // Paper
         // CraftBukkit start
         if (isOversleep) return canOversleep();// Paper - because of our changes, this logic is broken
         return this.forceTicks || this.isEntered() || SystemUtils.getMonotonicMillis() < (this.X ? this.W : this.nextTick);
@@ -1041,6 +1042,23 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
         });
     }
 
+    // Paper start
+    public int midTickChunksTasksRan = 0;
+    private long midTickLastRan = 0;
+    public void midTickLoadChunks() {
+        if (!isMainThread() || System.nanoTime() - midTickLastRan < 1000000) {
+            // only check once per 0.25ms incase this code is called in a hot method
+            return;
+        }
+        try (co.aikar.timings.Timing ignored = co.aikar.timings.MinecraftTimings.midTickChunkTasks.startTiming()) {
+            for (WorldServer value : this.getWorlds()) {
+                value.getChunkProvider().serverThreadQueue.midTickLoadChunks();
+            }
+            midTickLastRan = System.nanoTime();
+        }
+    }
+    // Paper end
+
     @Override
     protected TickTask postToMainThread(Runnable runnable) {
         return new TickTask(this.ticks, runnable);
@@ -1127,6 +1145,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
         // Paper start - move oversleep into full server tick
         isOversleep = true;MinecraftTimings.serverOversleep.startTiming();
         this.awaitTasks(() -> {
+            midTickLoadChunks(); // will only do loads since we are still considered !canSleepForTick
             return !this.canOversleep();
         });
         isOversleep = false;MinecraftTimings.serverOversleep.stopTiming();
@@ -1205,13 +1224,16 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
     }
 
     protected void b(BooleanSupplier booleansupplier) {
+        midTickLoadChunks(); // Paper
         MinecraftTimings.bukkitSchedulerTimer.startTiming(); // Spigot // Paper
         this.server.getScheduler().mainThreadHeartbeat(this.ticks); // CraftBukkit
         MinecraftTimings.bukkitSchedulerTimer.stopTiming(); // Spigot // Paper
+        midTickLoadChunks(); // Paper
         this.methodProfiler.enter("commandFunctions");
         MinecraftTimings.commandFunctionsTimer.startTiming(); // Spigot // Paper
         this.getFunctionData().tick();
         MinecraftTimings.commandFunctionsTimer.stopTiming(); // Spigot // Paper
+        midTickLoadChunks(); // Paper
         this.methodProfiler.exitEnter("levels");
         Iterator iterator = this.getWorlds().iterator();
 
@@ -1222,7 +1244,7 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
             processQueue.remove().run();
         }
         MinecraftTimings.processQueueTimer.stopTiming(); // Spigot
-
+        midTickLoadChunks(); // Paper
         MinecraftTimings.timeUpdateTimer.startTiming(); // Spigot // Paper
         // Send time updates to everyone, it will get the right time from the world the player is in.
         // Paper start - optimize time updates
@@ -1264,9 +1286,11 @@ public abstract class MinecraftServer extends IAsyncTaskHandlerReentrant<TickTas
             this.methodProfiler.enter("tick");
 
             try {
+                midTickLoadChunks(); // Paper
                 worldserver.timings.doTick.startTiming(); // Spigot
                 worldserver.doTick(booleansupplier);
                 worldserver.timings.doTick.stopTiming(); // Spigot
+                midTickLoadChunks(); // Paper
             } catch (Throwable throwable) {
                 // Spigot Start
                 CrashReport crashreport;
diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index 4f2c8a9fbfa4596f5414dd742affc4cc45deab5a..2cc9fd7aee91cc78156fc6001f0c461530a7f882 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -452,6 +452,7 @@ public class WorldServer extends World implements GeneratorAccessSeed {
         }
         timings.scheduledBlocks.stopTiming(); // Paper
 
+        this.getMinecraftServer().midTickLoadChunks(); // Paper
         gameprofilerfiller.exitEnter("raid");
         this.timings.raids.startTiming(); // Paper - timings
         this.persistentRaid.a();
@@ -460,6 +461,7 @@ public class WorldServer extends World implements GeneratorAccessSeed {
         timings.doSounds.startTiming(); // Spigot
         this.ah();
         timings.doSounds.stopTiming(); // Spigot
+        this.getMinecraftServer().midTickLoadChunks(); // Paper
         this.ticking = false;
         gameprofilerfiller.exitEnter("entities");
         boolean flag3 = true || !this.players.isEmpty() || !this.getForceLoadedChunks().isEmpty(); // CraftBukkit - this prevents entity cleanup, other issues on servers with no players
@@ -527,6 +529,7 @@ public class WorldServer extends World implements GeneratorAccessSeed {
             timings.entityTick.stopTiming(); // Spigot
 
             this.tickingEntities = false;
+            this.getMinecraftServer().midTickLoadChunks(); // Paper
 
             Entity entity2;
 
@@ -536,6 +539,7 @@ public class WorldServer extends World implements GeneratorAccessSeed {
             }
 
             timings.tickEntities.stopTiming(); // Spigot
+            this.getMinecraftServer().midTickLoadChunks(); // Paper
             this.tickBlockEntities();
         }