Paper/patches/server/0137-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 114f4017c4133042178c57d424f10079163835dd..aa52b271bd556a29f774fde375b713d0d187521b 100644
--- a/src/main/java/net/minecraft/Util.java
+++ b/src/main/java/net/minecraft/Util.java
@@ -89,6 +89,22 @@ public class Util {
     private static final ExecutorService BACKGROUND_EXECUTOR = makeExecutor("Main");
     private static final ExecutorService IO_POOL = makeIoExecutor("IO-Worker-", false);
     private static final ExecutorService 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);
     private static final int LINEAR_LOOKUP_THRESHOLD = 8;
     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 68f95f4782c1effdee13543b702fdcc78ce14353..fdf3194499512614355b02aa11e34574cdd89c59 100644
--- a/src/main/java/net/minecraft/server/players/GameProfileCache.java
+++ b/src/main/java/net/minecraft/server/players/GameProfileCache.java
@@ -170,7 +170,7 @@ 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 bffc770105800ba78c6d9bfb56ad9ad425f19910..92b770d10f34596ce52392a0db1ccd825108730b 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
@@ -80,7 +80,7 @@ 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
     }
 
     @Override
diff --git a/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java b/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
index 358af0121ce3d87a9f51da2bae0699034c1560b4..91e913f8652584ffab44c44d10c0e0c47707e261 100644
--- a/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
+++ b/src/main/java/org/bukkit/craftbukkit/profile/CraftPlayerProfile.java
@@ -122,7 +122,7 @@ 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() {