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.

paper-server/patches/sources/net/minecraft/Util.java.patch

@@ -1,6 +1,29 @@
 --- a/net/minecraft/Util.java
 +++ b/net/minecraft/Util.java
-@@ -136,7 +136,7 @@
+@@ -95,6 +95,22 @@
+     private static final TracingExecutor BACKGROUND_EXECUTOR = makeExecutor("Main");
+     private static final TracingExecutor IO_POOL = makeIoExecutor("IO-Worker-", false);
+     private static final TracingExecutor DOWNLOAD_POOL = makeIoExecutor("Download-", true);
++    // 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 DateTimeFormatter FILENAME_DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd_HH.mm.ss", Locale.ROOT);
+     public static final int LINEAR_LOOKUP_THRESHOLD = 8;
+     private static final Set<String> ALLOWED_UNTRUSTED_LINK_PROTOCOLS = Set.of("http", "https");
+@@ -136,7 +152,7 @@
      }
  
      public static long getNanos() {
@@ -9,7 +32,7 @@
      }
  
      public static long getEpochMillis() {
-@@ -537,7 +537,7 @@
+@@ -537,7 +553,7 @@
      public static <K extends Enum<K>, V> EnumMap<K, V> makeEnumMap(Class<K> enumClass, Function<K, V> mapper) {
          EnumMap<K, V> enumMap = new EnumMap<>(enumClass);
  

paper-server/patches/sources/net/minecraft/server/players/GameProfileCache.java.patch

@@ -51,6 +51,15 @@
          }
  
          return optional;
+@@ -167,7 +169,7 @@
+             } else {
+                 CompletableFuture<Optional<GameProfile>> completablefuture1 = CompletableFuture.supplyAsync(() -> {
+                     return this.get(username);
+-                }, Util.backgroundExecutor().forName("getProfile")).whenCompleteAsync((optional, throwable) -> {
++                }, Util.PROFILE_EXECUTOR).whenCompleteAsync((optional, throwable) -> { // Paper - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
+                     this.requests.remove(username);
+                 }, this.executor);
+ 
 @@ -208,7 +210,7 @@
  
              label54:

paper-server/patches/sources/net/minecraft/world/level/block/entity/SkullBlockEntity.java.patch

@@ -0,0 +1,11 @@
+--- a/net/minecraft/world/level/block/entity/SkullBlockEntity.java
++++ b/net/minecraft/world/level/block/entity/SkullBlockEntity.java
+@@ -105,7 +105,7 @@
+                 ProfileResult profileResult = apiServices.sessionService().fetchProfile(uuid, true);
+                 return Optional.ofNullable(profileResult).map(ProfileResult::profile);
+             }
+-        }, Util.backgroundExecutor().forName("fetchProfile"));
++        }, Util.PROFILE_EXECUTOR); // Paper - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
+     }
+ 
+     public static void clear() {

paper-server/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java

@@ -161,7 +161,7 @@ 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 - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
     }
 
     private CraftPlayerProfile getUpdatedProfile() {