Paper/patches/server/0138-Do-not-submit-profile-lookups-to-worldgen-threads.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sun, 8 Aug 2021 16:26:46 -0700
Subject: [PATCH] Do not submit profile lookups to worldgen threads

They block. On network I/O.

If enough tasks are submitted the server will eventually stall
out due to a sync load, as the worldgen threads will be
stalling on profile lookups.

diff --git a/src/main/java/net/minecraft/Util.java b/src/main/java/net/minecraft/Util.java
index d7e22ddf89619b58516ccef1d75a4c33df61b73c..33ec7786cdf8c32e905d192fc8364418e47404d5 100644
--- a/src/main/java/net/minecraft/Util.java
+++ b/src/main/java/net/minecraft/Util.java
@@ -80,6 +80,22 @@ public class Util {
     private static final AtomicInteger WORKER_COUNT = new AtomicInteger(1);
     private static final ExecutorService BOOTSTRAP_EXECUTOR = makeExecutor("Bootstrap");
     private static final ExecutorService BACKGROUND_EXECUTOR = makeExecutor("Main");
+    // Paper start - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
+    public static final ExecutorService PROFILE_EXECUTOR = Executors.newFixedThreadPool(2, new java.util.concurrent.ThreadFactory() {
+
+        private final AtomicInteger count = new AtomicInteger();
+
+        @Override
+        public Thread newThread(Runnable run) {
+            Thread ret = new Thread(run);
+            ret.setName("Profile Lookup Executor #" + this.count.getAndIncrement());
+            ret.setUncaughtExceptionHandler((Thread thread, Throwable throwable) -> {
+                LOGGER.error("Uncaught exception in thread " + thread.getName(), throwable);
+            });
+            return ret;
+        }
+    });
+    // Paper end - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
     private static final ExecutorService IO_POOL = makeIoExecutor();
     public static LongSupplier timeSource = System::nanoTime;
     public static final Ticker TICKER = new Ticker() {
diff --git a/src/main/java/net/minecraft/server/players/GameProfileCache.java b/src/main/java/net/minecraft/server/players/GameProfileCache.java
index c7edbd12361cfd3dcf1359917d579fae4c3cc8a7..6c8a1d9c7696fa55dae6ba5e4ea50a0ffc7ea543 100644
--- a/src/main/java/net/minecraft/server/players/GameProfileCache.java
+++ b/src/main/java/net/minecraft/server/players/GameProfileCache.java
@@ -181,7 +181,7 @@ public class GameProfileCache {
             } else {
                 this.requests.put(username, CompletableFuture.supplyAsync(() -> {
                     return this.get(username);
-                }, Util.backgroundExecutor()).whenCompleteAsync((optional, throwable) -> {
+                }, Util.PROFILE_EXECUTOR).whenCompleteAsync((optional, throwable) -> { // Paper - not a good idea to use BLOCKING OPERATIONS on the worldgen executor
                     this.requests.remove(username);
                 }, this.executor).whenCompleteAsync((optional, throwable) -> {
                     consumer.accept(optional);
diff --git a/src/main/java/net/minecraft/world/level/block/entity/SkullBlockEntity.java b/src/main/java/net/minecraft/world/level/block/entity/SkullBlockEntity.java
index 0c7e29b589ab106013d979a20edc415b4b32a677..c5d5d90d10b30f30d1262367b3d75df43fbdb231 100644
--- a/src/main/java/net/minecraft/world/level/block/entity/SkullBlockEntity.java
+++ b/src/main/java/net/minecraft/world/level/block/entity/SkullBlockEntity.java
@@ -120,7 +120,7 @@ public class SkullBlockEntity extends BlockEntity {
     public static void updateGameprofile(@Nullable GameProfile owner, Consumer<GameProfile> callback) {
         if (owner != null && !StringUtil.isNullOrEmpty(owner.getName()) && (!owner.isComplete() || !owner.getProperties().containsKey("textures")) && profileCache != null && sessionService != null) {
             profileCache.getAsync(owner.getName(), (profile) -> {
-                Util.backgroundExecutor().execute(() -> {
+                Util.PROFILE_EXECUTOR.execute(() -> { // Paper - not a good idea to use BLOCKING OPERATIONS on the worldgen executor
                     Util.ifElse(profile, (profilex) -> {
                         Property property = Iterables.getFirst(profilex.getProperties().get("textures"), (Property)null);
                         if (property == null) {
diff --git a/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java b/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
index 2d49bd6f3f017d43dfaa23cedf35040b64bcdcf8..9edc5e73819e0b55372f77c5e292eece74d837c7 100644
--- a/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
+++ b/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
@@ -121,7 +121,7 @@ public final class CraftPlayerProfile implements PlayerProfile {
 
     @Override
     public CompletableFuture<PlayerProfile> update() {
-        return CompletableFuture.supplyAsync(this::getUpdatedProfile, Util.backgroundExecutor());
+        return CompletableFuture.supplyAsync(this::getUpdatedProfile, Util.PROFILE_EXECUTOR); // Paper - not a good idea to use BLOCKING OPERATIONS on the worldgen executor
     }
 
     private CraftPlayerProfile getUpdatedProfile() {