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/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index 939170ade7c24bcf1c358f00931f867599cf9d54..786eafffa9bc51399c7fdf0012dfdaa9c92e71b0 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -1302,6 +1302,7 @@ 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()) {
@@ -2624,4 +2625,74 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
         }
     }
     // Paper end
+
+    // 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
 }
diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index 108164945f2aa088834585d9d80274ea551608d9..6058a6d30880f789244e4054cadd43941b7778bd 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -1012,6 +1012,7 @@ public class ServerChunkCache extends ChunkSource {
                 iterator1 = shuffled.iterator();
             }
 
+            int chunksTicked = 0; // Paper
             try {
             while (iterator1.hasNext()) {
                 LevelChunk chunk1 = iterator1.next();
@@ -1029,6 +1030,7 @@ public class ServerChunkCache extends ChunkSource {
 
                     if (this.level.shouldTickBlocksAt(chunkcoordintpair.toLong())) {
                         this.level.tickChunk(chunk1, k);
+                        if ((chunksTicked++ & 1) == 0) net.minecraft.server.MinecraftServer.getServer().executeMidTickTasks(); // Paper
                     }
                 }
                 // Paper start - optimise chunk tick iteration
diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
index 18f28b5ea2919fb12fd1e76555026c2161564372..07f5c61fc3da270215133d2d0240e96f701a6216 100644
--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
@@ -209,6 +209,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
     private final StructureManager structureManager;
     private final StructureCheck structureCheck;
     private final boolean tickTime;
+    public long lastMidTickExecuteFailure; // Paper - execute chunk tasks mid tick
 
     // CraftBukkit start
     public final LevelStorageSource.LevelStorageAccess convertable;
@@ -983,6 +984,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
         if (fluid1.is(fluid)) {
             fluid1.tick(this, pos);
         }
+        MinecraftServer.getServer().executeMidTickTasks(); // Paper - exec chunk tasks during world tick
 
     }
 
@@ -992,6 +994,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
         if (iblockdata.is(block)) {
             iblockdata.tick(this, pos, this.random);
         }
+        MinecraftServer.getServer().executeMidTickTasks(); // Paper - exec chunk tasks during world tick
 
     }
 
diff --git a/src/main/java/net/minecraft/world/level/Level.java b/src/main/java/net/minecraft/world/level/Level.java
index e613d3171200dc436a45bd1980a106d936e351cd..f9ffdeb250e472180616d5b7e944b69e17a217dd 100644
--- a/src/main/java/net/minecraft/world/level/Level.java
+++ b/src/main/java/net/minecraft/world/level/Level.java
@@ -795,6 +795,11 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
                 // Spigot end
             } else if (this.shouldTickBlocksAt(tickingblockentity.getPos())) {
                 tickingblockentity.tick();
+                // Paper start - execute chunk tasks during tick
+                if ((this.tileTickPosition & 7) == 0) {
+                    MinecraftServer.getServer().executeMidTickTasks();
+                }
+                // Paper end - execute chunk tasks during tick
             }
         }
         this.blockEntityTickers.removeAll(toRemove);
@@ -809,6 +814,7 @@ 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