Paper/patches/server/0139-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 9870eccc1dc5c2201f12f8e2affe647f6b0375f8..30237ca94a36197ce21369bdcc7bb1dfafe02680 100644
--- a/src/main/java/net/minecraft/Util.java
+++ b/src/main/java/net/minecraft/Util.java
@@ -82,6 +82,22 @@ public class Util {
     private static final String MAX_THREADS_SYSTEM_PROPERTY = "max.bg.threads";
     private static final AtomicInteger WORKER_COUNT = new AtomicInteger(1);
     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();
     private static final DateTimeFormatter FILENAME_DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd_HH.mm.ss", Locale.ROOT);
     public static final long NANOS_PER_MILLI = 1000000L;
diff --git a/src/main/java/net/minecraft/server/players/GameProfileCache.java b/src/main/java/net/minecraft/server/players/GameProfileCache.java
index 82f6404e5c4c5b2c9aea1b1c27ebee1d3c7ee9dc..c70cd016e1978931d115cfca94664897f0158196 100644
--- a/src/main/java/net/minecraft/server/players/GameProfileCache.java
+++ b/src/main/java/net/minecraft/server/players/GameProfileCache.java
@@ -167,7 +167,7 @@ public class GameProfileCache {
             } else {
                 CompletableFuture<Optional<GameProfile>> completablefuture1 = 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);
 
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 cf7e64eac9e3eb395a0be0a2a4fa0175a731b6e7..f5162f7171c348ff523b18e577246561d79e1c20 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
@@ -222,7 +222,7 @@ public class SkullBlockEntity extends BlockEntity {
             } else {
                 return Optional.empty();
             }
-        }, Util.backgroundExecutor());
+        }, Util.PROFILE_EXECUTOR); // Paper - not a good idea to use BLOCKING OPERATIONS on the worldgen executor
     }
 
     private static boolean hasTextures(GameProfile profile) {
diff --git a/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java b/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
index 5a21cc441e1c925a7674299073ac374e63b911ec..ac05e268c9f00bca9f8ac19650937eede711810b 100644
--- a/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
+++ b/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
@@ -125,7 +125,7 @@ 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() {