From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <spottedleaf@spottedleaf.dev>
Date: Mon, 6 Apr 2020 04:20:44 -0700
Subject: [PATCH] Execute chunk tasks mid-tick

This will help the server load chunks if tick times are high.

diff --git a/src/main/java/co/aikar/timings/MinecraftTimings.java b/src/main/java/co/aikar/timings/MinecraftTimings.java
index b27021a42cbed3f0648a8d0903d00d03922ae221..eada966d7f108a6081be7a848f5c1dfcb1eed676 100644
--- a/src/main/java/co/aikar/timings/MinecraftTimings.java
+++ b/src/main/java/co/aikar/timings/MinecraftTimings.java
@@ -45,6 +45,8 @@ public final class MinecraftTimings {
     public static final Timing antiXrayUpdateTimer = Timings.ofSafe("anti-xray - update");
     public static final Timing antiXrayObfuscateTimer = Timings.ofSafe("anti-xray - obfuscate");
 
+    public static final Timing midTickChunkTasks = Timings.ofSafe("Mid Tick Chunk Tasks");
+
     private static final Map<Class<?>, String> taskNameCache = new MapMaker().weakKeys().makeMap();
 
     private MinecraftTimings() {}
diff --git a/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java b/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java
index 5fdaefc128956581be4bb9b34199fd6410563991..b7edc1121797bc1c57e25f540ed0124fa8b36b7a 100644
--- a/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java
+++ b/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java
@@ -312,6 +312,7 @@ public final class PaperTickList<T> extends ServerTickList<T> { // extend to avo
                     toTick.tickState = STATE_SCHEDULED;
                     this.addToNotTickingReady(toTick);
                 }
+                MinecraftServer.getServer().executeMidTickTasks(); // Paper - exec chunk tasks during world tick
             } catch (final Throwable thr) {
                 // start copy from TickListServer // TODO check on update
                 CrashReport crashreport = CrashReport.forThrowable(thr, "Exception while ticking");
diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index 71181012314d20e3505543a6d2abe88cb8e17a27..4778d45d14317d78ae1988de18f675d997d28c98 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -330,6 +330,76 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
         return s0;
     }
 
+    // Paper start - execute chunk tasks mid tick
+    static final long CHUNK_TASK_QUEUE_BACKOFF_MIN_TIME = 25L * 1000L; // 25us
+    static final long MAX_CHUNK_EXEC_TIME = 1000L; // 1us
+
+    static final long TASK_EXECUTION_FAILURE_BACKOFF = 5L * 1000L; // 5us
+
+    private static long lastMidTickExecute;
+    private static long lastMidTickExecuteFailure;
+
+    private boolean tickMidTickTasks() {
+        // give all worlds a fair chance at by targetting them all.
+        // if we execute too many tasks, that's fine - we have logic to correctly handle overuse of allocated time.
+        boolean executed = false;
+        for (ServerLevel world : this.getAllLevels()) {
+            long currTime = System.nanoTime();
+            if (currTime - world.lastMidTickExecuteFailure <= TASK_EXECUTION_FAILURE_BACKOFF) {
+                continue;
+            }
+            if (!world.getChunkSource().pollTask()) {
+                // we need to back off if this fails
+                world.lastMidTickExecuteFailure = currTime;
+            } else {
+                executed = true;
+            }
+        }
+
+        return executed;
+    }
+
+    public final void executeMidTickTasks() {
+        org.spigotmc.AsyncCatcher.catchOp("mid tick chunk task execution");
+        long startTime = System.nanoTime();
+        if ((startTime - lastMidTickExecute) <= CHUNK_TASK_QUEUE_BACKOFF_MIN_TIME || (startTime - lastMidTickExecuteFailure) <= TASK_EXECUTION_FAILURE_BACKOFF) {
+            // it's shown to be bad to constantly hit the queue (chunk loads slow to a crawl), even if no tasks are executed.
+            // so, backoff to prevent this
+            return;
+        }
+
+        co.aikar.timings.MinecraftTimings.midTickChunkTasks.startTiming();
+        try {
+            for (;;) {
+                boolean moreTasks = this.tickMidTickTasks();
+                long currTime = System.nanoTime();
+                long diff = currTime - startTime;
+
+                if (!moreTasks || diff >= MAX_CHUNK_EXEC_TIME) {
+                    if (!moreTasks) {
+                        lastMidTickExecuteFailure = currTime;
+                    }
+
+                    // note: negative values reduce the time
+                    long overuse = diff - MAX_CHUNK_EXEC_TIME;
+                    if (overuse >= (10L * 1000L * 1000L)) { // 10ms
+                        // make sure something like a GC or dumb plugin doesn't screw us over...
+                        overuse = 10L * 1000L * 1000L; // 10ms
+                    }
+
+                    double overuseCount = (double)overuse/(double)MAX_CHUNK_EXEC_TIME;
+                    long extraSleep = (long)Math.round(overuseCount*CHUNK_TASK_QUEUE_BACKOFF_MIN_TIME);
+
+                    lastMidTickExecute = currTime + extraSleep;
+                    return;
+                }
+            }
+        } finally {
+            co.aikar.timings.MinecraftTimings.midTickChunkTasks.stopTiming();
+        }
+    }
+    // Paper end - execute chunk tasks mid tick
+
     public MinecraftServer(OptionSet options, DataPackConfig datapackconfiguration, Thread thread, RegistryAccess.RegistryHolder iregistrycustom_dimension, LevelStorageSource.LevelStorageAccess convertable_conversionsession, WorldData savedata, PackRepository resourcepackrepository, Proxy proxy, DataFixer datafixer, ServerResources datapackresources, @Nullable MinecraftSessionService minecraftsessionservice, @Nullable GameProfileRepository gameprofilerepository, @Nullable GameProfileCache usercache, ChunkProgressListenerFactory worldloadlistenerfactory) {
         super("Server");
         SERVER = this; // Paper - better singleton
@@ -1325,6 +1395,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
 
     private boolean pollTaskInternal() {
         if (super.pollTask()) {
+            this.executeMidTickTasks(); // Paper - execute chunk tasks mid tick
             return true;
         } else {
             if (this.haveTime()) {
diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index 7ea86cbeb72f08d751c14006f428fe5921916061..108f2212f8bd00247bf73ff4f3ba42830abad459 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -1022,6 +1022,7 @@ public class ServerChunkCache extends ChunkSource {
                 Collections.shuffle(shuffled);
                 iterator = shuffled.iterator();
             }
+            int chunksTicked = 0; // Paper
             try { while (iterator.hasNext()) {
                 LevelChunk chunk = iterator.next();
                 ChunkHolder playerchunk = chunk.playerChunk;
@@ -1044,6 +1045,7 @@ public class ServerChunkCache extends ChunkSource {
                         this.level.tickChunk(chunk, k);
                         // this.level.timings.doTickTiles.stopTiming(); // Spigot // Paper
                     }
+                    if ((chunksTicked++ & 1) == 0) net.minecraft.server.MinecraftServer.getServer().executeMidTickTasks(); // Paper
                 }
             } // Paper start - optimise chunk tick iteration
             } finally {
diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
index 675fca76f5f7319d45e0d4f03b74d27bf2a5a647..9c4f8d59ece0222bb2b7c8aa3b0a0044b8205e77 100644
--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
@@ -190,7 +190,9 @@ public class ServerLevel extends Level implements WorldGenLevel {
     final Int2ObjectMap<EnderDragonPart> dragonParts;
     private final StructureFeatureManager structureFeatureManager;
     private final boolean tickTime;
-
+    // Paper start - execute chunk tasks mid tick
+    public long lastMidTickExecuteFailure;
+    // Paper end - execute chunk tasks mid tick
 
     // CraftBukkit start
     private int tickPosition;
diff --git a/src/main/java/net/minecraft/world/level/Level.java b/src/main/java/net/minecraft/world/level/Level.java
index bdd50c28a76576be7950e3ccf8e00b622f3860d1..6818de8db716a3d4bcf8a6ee4dc6acccf441cddb 100644
--- a/src/main/java/net/minecraft/world/level/Level.java
+++ b/src/main/java/net/minecraft/world/level/Level.java
@@ -914,6 +914,7 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
     public <T extends Entity> void guardEntityTick(Consumer<T> tickConsumer, T entity) {
         try {
             tickConsumer.accept(entity);
+            MinecraftServer.getServer().executeMidTickTasks(); // Paper - execute chunk tasks mid tick
         } catch (Throwable throwable) {
             if (throwable instanceof ThreadDeath) throw throwable; // Paper
             // Paper start - Prevent tile entity and entity crashes